Release: 2.0.43 | Release Date: August 11, 2025

# SQLAlchemy 2.0 Documentation

# 0.5 Changelog

## 0.5.9

no release date

### sql

- [sql]

  Fixed erroneous self_group() call in expression package.

  References: #1661

## 0.5.8

Released: Sat Jan 16 2010

### sql

- [sql]

  The copy() method on Column now supports uninitialized, unnamed Column objects. This allows easy creation of declarative helpers which place common columns on multiple subclasses.

- [sql]

  Default generators like Sequence() translate correctly across a copy() operation.

- [sql]

  Sequence() and other DefaultGenerator objects are accepted as the value for the “default” and “onupdate” keyword arguments of Column, in addition to being accepted positionally.

- [sql]

  Fixed a column arithmetic bug that affected column correspondence for cloned selectables which contain free-standing column expressions. This bug is generally only noticeable when exercising newer ORM behavior only available in 0.6 via, but is more correct at the SQL expression level as well.

  References: #1568, #1617

### postgresql

- [postgresql]

  The extract() function, which was slightly improved in 0.5.7, needed a lot more work to generate the correct typecast (the typecasts appear to be necessary in PG’s EXTRACT quite a lot of the time). The typecast is now generated using a rule dictionary based on PG’s documentation for date/time/interval arithmetic. It also accepts text() constructs again, which was broken in 0.5.7.

  References: #1647

### misc

- [firebird]

  Recognize more errors as disconnections.

  References: #1646

## 0.5.7

Released: Sat Dec 26 2009

### orm

- [orm]

  contains_eager() now works with the automatically generated subquery that results when you say “query(Parent).join(Parent.somejoinedsubclass)”, i.e. when Parent joins to a joined-table-inheritance subclass. Previously contains_eager() would erroneously add the subclass table to the query separately producing a cartesian product. An example is in the ticket description.

  References: #1543

- [orm]

  query.options() now only propagate to loaded objects for potential further sub-loads only for options where such behavior is relevant, keeping various unserializable options like those generated by contains_eager() out of individual instance states.

  References: #1553

- [orm]

  Session.execute() now locates table- and mapper-specific binds based on a passed in expression which is an insert()/update()/delete() construct.

  References: #1054

- [orm]

  Session.merge() now properly overwrites a many-to-one or uselist=False attribute to None if the attribute is also None in the given object to be merged.

- [orm]

  Fixed a needless select which would occur when merging transient objects that contained a null primary key identifier.

  References: #1618

- [orm]

  Mutable collection passed to the “extension” attribute of relation(), column_property() etc. will not be mutated or shared among multiple instrumentation calls, preventing duplicate extensions, such as backref populators, from being inserted into the list.

  References: #1585

- [orm]

  Fixed the call to get_committed_value() on CompositeProperty.

  References: #1504

- [orm]

  Fixed bug where Query would crash if a join() with no clear “left” side were called when a non-mapped column entity appeared in the columns list.

  References: #1602

- [orm]

  Fixed bug whereby composite columns wouldn’t load properly when configured on a joined-table subclass, introduced in version 0.5.6 as a result of the fix for. thx to Scott Torborg.

  References: #1480, #1616

- [orm]

  The “use get” behavior of many-to-one relations, i.e. that a lazy load will fallback to the possibly cached query.get() value, now works across join conditions where the two compared types are not exactly the same class, but share the same “affinity” - i.e. Integer and SmallInteger. Also allows combinations of reflected and non-reflected types to work with 0.5 style type reflection, such as PGText/Text (note 0.6 reflects types as their generic versions).

  References: #1556

- [orm]

  Fixed bug in query.update() when passing Cls.attribute as keys in the value dict and using synchronize_session=’expire’ (‘fetch’ in 0.6).

  References: #1436

### sql

- [sql]

  Fixed bug in two-phase transaction whereby commit() method didn’t set the full state which allows subsequent close() call to succeed.

  References: #1603

- [sql]

  Fixed the “numeric” paramstyle, which apparently is the default paramstyle used by Informixdb.

- [sql]

  Repeat expressions in the columns clause of a select are deduped based on the identity of each clause element, not the actual string. This allows positional elements to render correctly even if they all render identically, such as “qmark” style bind parameters.

  References: #1574

- [sql]

  The cursor associated with connection pool connections (i.e. _CursorFairy) now proxies __iter__() to the underlying cursor correctly.

  References: #1632

- [sql]

  types now support an “affinity comparison” operation, i.e. that an Integer/SmallInteger are “compatible”, or a Text/String, PickleType/Binary, etc. Part of.

  References: #1556

- [sql]

  Fixed bug preventing alias() of an alias() from being cloned or adapted (occurs frequently in ORM operations).

  References: #1641

### postgresql

- [postgresql]

  Added support for reflecting the DOUBLE PRECISION type, via a new postgres.PGDoublePrecision object. This is postgresql.DOUBLE_PRECISION in 0.6.

  References: #1085

- [postgresql]

  Added support for reflecting the INTERVAL YEAR TO MONTH and INTERVAL DAY TO SECOND syntaxes of the INTERVAL type.

  References: #460

- [postgresql]

  Corrected the “has_sequence” query to take current schema, or explicit sequence-stated schema, into account.

  References: #1576

- [postgresql]

  Fixed the behavior of extract() to apply operator precedence rules to the “::” operator when applying the “timestamp” cast - ensures proper parenthesization.

  References: #1611

### sqlite

- [sqlite]

  sqlite dialect properly generates CREATE INDEX for a table that is in an alternate schema.

  References: #1439

### mssql

- [mssql]

  Changed the name of TrustedConnection to Trusted_Connection when constructing pyodbc connect arguments

  References: #1561

### oracle

- [oracle]

  The “table_names” dialect function, used by MetaData .reflect(), omits “index overflow tables”, a system table generated by Oracle when “index only tables” with overflow are used. These tables aren’t accessible via SQL and can’t be reflected.

  References: #1637

### misc

- [ext]

  A column can be added to a joined-table declarative superclass after the class has been constructed (i.e. via class-level attribute assignment), and the column will be propagated down to subclasses. This is the reverse situation as that of, fixed in 0.5.6.

  References: #1523, #1570

- [ext]

  Fixed a slight inaccuracy in the sharding example. Comparing equivalence of columns in the ORM is best accomplished using col1.shares_lineage(col2).

  References: #1491

- [ext]

  Removed unused load() method from ShardedQuery.

  References: #1606

## 0.5.6

Released: Sat Sep 12 2009

### orm

- [orm]

  Fixed bug whereby inheritance discriminator part of a composite primary key would fail on updates. Continuation of.

  References: #1300

- [orm]

  Fixed bug which disallowed one side of a many-to-many bidirectional reference to declare itself as “viewonly”

  References: #1507

- [orm]

  Added an assertion that prevents a @validates function or other AttributeExtension from loading an unloaded collection such that internal state may be corrupted.

  References: #1526

- [orm]

  Fixed bug which prevented two entities from mutually replacing each other’s primary key values within a single flush() for some orderings of operations.

  References: #1519

- [orm]

  Fixed an obscure issue whereby a joined-table subclass with a self-referential eager load on the base class would populate the related object’s “subclass” table with data from the “subclass” table of the parent.

  References: #1485

- [orm]

  relations() now have greater ability to be “overridden”, meaning a subclass that explicitly specifies a relation() overriding that of the parent class will be honored during a flush. This is currently to support many-to-many relations from concrete inheritance setups. Outside of that use case, YMMV.

  References: #1477

- [orm]

  Squeezed a few more unnecessary “lazy loads” out of relation(). When a collection is mutated, many-to-one backrefs on the other side will not fire off to load the “old” value, unless “single_parent=True” is set. A direct assignment of a many-to-one still loads the “old” value in order to update backref collections on that value, which may be present in the session already, thus maintaining the 0.5 behavioral contract.

  References: #1483

- [orm]

  Fixed bug whereby a load/refresh of joined table inheritance attributes which were based on column_property() or similar would fail to evaluate.

  References: #1480

- [orm]

  Improved support for MapperProperty objects overriding that of an inherited mapper for non-concrete inheritance setups - attribute extensions won’t randomly collide with each other.

  References: #1488

- [orm]

  UPDATE and DELETE do not support ORDER BY, LIMIT, OFFSET, etc. in standard SQL. Query.update() and Query.delete() now raise an exception if any of limit(), offset(), order_by(), group_by(), or distinct() have been called.

  References: #1487

- [orm]

  Added AttributeExtension to sqlalchemy.orm.__all__

- [orm]

  Improved error message when query() is called with a non-SQL /entity expression.

  References: #1476

- [orm]

  Using False or 0 as a polymorphic discriminator now works on the base class as well as a subclass.

  References: #1440

- [orm]

  Added enable_assertions(False) to Query which disables the usual assertions for expected state - used by Query subclasses to engineer custom state.. See https://www.sqlalchemy.org/trac/wiki/UsageRecipes/PreFilteredQuery for an example.

  References: #1424

- [orm]

  Fixed recursion issue which occurred if a mapped object’s __len__() or __nonzero__() method resulted in state changes.

  References: #1501

- [orm]

  Fixed incorrect exception raise in Weak/StrongIdentityMap.add()

  References: #1506

- [orm]

  Fixed the error message for “could not find a FROM clause” in query.join() which would fail to issue correctly if the query was against a pure SQL construct.

  References: #1522

- [orm]

  Fixed a somewhat hypothetical issue which would result in the wrong primary key being calculated for a mapper using the old polymorphic_union function - but this is old stuff.

  References: #1486

### sql

- [sql]

  Fixed column.copy() to copy defaults and onupdates.

  References: #1373

- [sql]

  Fixed a bug in extract() introduced in 0.5.4 whereby the string “field” argument was getting treated as a ClauseElement, causing various errors within more complex SQL transformations.

- [sql]

  Unary expressions such as DISTINCT propagate their type handling to result sets, allowing conversions like unicode and such to take place.

  References: #1420

- [sql]

  Fixed bug in Table and Column whereby passing empty dict for “info” argument would raise an exception.

  References: #1482

### oracle

- [oracle]

  Backported 0.6 fix for Oracle alias names not getting truncated.

  References: #1309

### misc

- [ext]

  The collection proxies produced by associationproxy are now pickleable. A user-defined proxy_factory however is still not pickleable unless it defines __getstate__ and __setstate__.

  References: #1446

- [ext]

  Declarative will raise an informative exception if __table_args__ is passed as a tuple with no dict argument. Improved documentation.

  References: #1468

- [ext]

  Table objects declared in the MetaData can now be used in string expressions sent to primaryjoin/secondaryjoin/ secondary - the name is pulled from the MetaData of the declarative base.

  References: #1527

- [ext]

  A column can be added to a joined-table subclass after the class has been constructed (i.e. via class-level attribute assignment). The column is added to the underlying Table as always, but now the mapper will rebuild its “join” to include the new column, instead of raising an error about “no such column, use column_property() instead”.

  References: #1523

- [test]

  Added examples into the test suite so they get exercised regularly and cleaned up a couple deprecation warnings.

## 0.5.5

Released: Mon Jul 13 2009

### general

- [general]

  unit tests have been migrated from unittest to nose. See README.unittests for information on how to run the tests.

  References: #970

### orm

- [orm]

  The “foreign_keys” argument of relation() will now propagate automatically to the backref in the same way that primaryjoin and secondaryjoin do. For the extremely rare use case where the backref of a relation() has intentionally different “foreign_keys” configured, both sides now need to be configured explicitly (if they do in fact require this setting, see the next note…).

- [orm]

  …the only known (and really, really rare) use case where a different foreign_keys setting was used on the forwards/backwards side, a composite foreign key that partially points to its own columns, has been enhanced such that the fk->itself aspect of the relation won’t be used to determine relation direction.

- [orm]

  Session.mapper is now deprecated.

  Call session.add() if you’d like a free-standing object to be part of your session. Otherwise, a DIY version of Session.mapper is now documented at https://www.sqlalchemy.org/trac/wiki/UsageRecipes/SessionAwareMapper The method will remain deprecated throughout 0.6.

- [orm]

  Fixed Query being able to join() from individual columns of a joined-table subclass entity, i.e. query(SubClass.foo, SubClass.bar).join(<anything>). In most cases, an error “Could not find a FROM clause to join from” would be raised. In a few others, the result would be returned in terms of the base class rather than the subclass - so applications which relied on this erroneous result need to be adjusted.

  References: #1431

- [orm]

  Fixed a bug involving contains_eager(), which would apply itself to a secondary (i.e. lazy) load in a particular rare case, producing cartesian products. improved the targeting of query.options() on secondary loads overall.

  References: #1461

- [orm]

  Fixed bug introduced in 0.5.4 whereby Composite types fail when default-holding columns are flushed.

- [orm]

  Fixed another 0.5.4 bug whereby mutable attributes (i.e. PickleType) wouldn’t be deserialized correctly when the whole object was serialized.

  References: #1426

- [orm]

  Fixed bug whereby session.is_modified() would raise an exception if any synonyms were in use.

- [orm]

  Fixed potential memory leak whereby previously pickled objects placed back in a session would not be fully garbage collected unless the Session were explicitly closed out.

- [orm]

  Fixed bug whereby list-based attributes, like pickletype and PGArray, failed to be merged() properly.

- [orm]

  Repaired non-working attributes.set_committed_value function.

- [orm]

  Trimmed the pickle format for InstanceState which should further reduce the memory footprint of pickled instances. The format should be backwards compatible with that of 0.5.4 and previous.

- [orm]

  sqlalchemy.orm.join and sqlalchemy.orm.outerjoin are now added to __all__ in sqlalchemy.orm.*.

  References: #1463

- [orm]

  Fixed bug where Query exception raise would fail when a too-short composite primary key value were passed to get().

  References: #1458

### sql

- [sql]

  Removed an obscure feature of execute() (including connection, engine, Session) whereby a bindparam() construct can be sent as a key to the params dictionary. This usage is undocumented and is at the core of an issue whereby the bindparam() object created implicitly by a text() construct may have the same hash value as a string placed in the params dictionary and may result in an inappropriate match when computing the final bind parameters. Internal checks for this condition would add significant latency to the critical task of parameter rendering, so the behavior is removed. This is a backwards incompatible change for any application that may have been using this feature, however the feature has never been documented.

### misc

- [engine/pool]

  Implemented recreate() for StaticPool.

## 0.5.4p2

Released: Tue May 26 2009

### sql

- [sql]

  Repaired the printing of SQL exceptions which are not based on parameters or are not executemany() style.

### postgresql

- [postgresql]

  Deprecated the hardcoded TIMESTAMP function, which when used as func.TIMESTAMP(value) would render “TIMESTAMP value”. This breaks on some platforms as PostgreSQL doesn’t allow bind parameters to be used in this context. The hard-coded uppercase is also inappropriate and there’s lots of other PG casts that we’d need to support. So instead, use text constructs i.e. select([“timestamp ‘12/05/09’”]).

## 0.5.4p1

Released: Mon May 18 2009

### orm

- [orm]

  Fixed an attribute error introduced in 0.5.4 which would occur when merge() was used with an incomplete object.

## 0.5.4

Released: Sun May 17 2009

### orm

- [orm]

  Significant performance enhancements regarding Sessions/flush() in conjunction with large mapper graphs, large numbers of objects:

  - Removed all* O(N) scanning behavior from the flush() process, i.e. operations that were scanning the full session, including an extremely expensive one that was erroneously assuming primary key values were changing when this was not the case.

    - one edge case remains which may invoke a full scan, if an existing primary key attribute is modified to a new value.

  - The Session’s “weak referencing” behavior is now full - no strong references whatsoever are made to a mapped object or related items/collections in its __dict__. Backrefs and other cycles in objects no longer affect the Session’s ability to lose all references to unmodified objects. Objects with pending changes still are maintained strongly until flush.

    The implementation also improves performance by moving the “resurrection” process of garbage collected items to only be relevant for mappings that map “mutable” attributes (i.e. PickleType, composite attrs). This removes overhead from the gc process and simplifies internal behavior.

    If a “mutable” attribute change is the sole change on an object which is then dereferenced, the mapper will not have access to other attribute state when the UPDATE is issued. This may present itself differently to some MapperExtensions.

    The change also affects the internal attribute API, but not the AttributeExtension interface nor any of the publicly documented attribute functions.

  - The unit of work no longer generates a graph of “dependency” processors for the full graph of mappers during flush(), instead creating such processors only for those mappers which represent objects with pending changes. This saves a tremendous number of method calls in the context of a large interconnected graph of mappers.

  - Cached a wasteful “table sort” operation that previously occurred multiple times per flush, also removing significant method call count from flush().

  - Other redundant behaviors have been simplified in mapper._save_obj().

  References: #1398

- [orm]

  Modified query_cls on DynamicAttributeImpl to accept a full mixin version of the AppenderQuery, which allows subclassing the AppenderMixin.

- [orm]

  The “polymorphic discriminator” column may be part of a primary key, and it will be populated with the correct discriminator value.

  References: #1300

- [orm]

  Fixed the evaluator not being able to evaluate IS NULL clauses.

- [orm]

  Fixed the “set collection” function on “dynamic” relations to initiate events correctly. Previously a collection could only be assigned to a pending parent instance, otherwise modified events would not be fired correctly. Set collection is now compatible with merge(), fixes.

  References: #1352

- [orm]

  Allowed pickling of PropertyOption objects constructed with instrumented descriptors; previously, pickle errors would occur when pickling an object which was loaded with a descriptor-based option, such as query.options(eagerload(MyClass.foo)).

- [orm]

  Lazy loader will not use get() if the “lazy load” SQL clause matches the clause used by get(), but contains some parameters hardcoded. Previously the lazy strategy would fail with the get(). Ideally get() would be used with the hardcoded parameters but this would require further development.

  References: #1357

- [orm]

  MapperOptions and other state associated with query.options() is no longer bundled within callables associated with each lazy/deferred-loading attribute during a load. The options are now associated with the instance’s state object just once when it’s populated. This removes the need in most cases for per-instance/attribute loader objects, improving load speed and memory overhead for individual instances.

  References: #1391

- [orm]

  Fixed another location where autoflush was interfering with session.merge(). autoflush is disabled completely for the duration of merge() now.

  References: #1360

- [orm]

  Fixed bug which prevented “mutable primary key” dependency logic from functioning properly on a one-to-one relation().

  References: #1406

- [orm]

  Fixed bug in relation(), introduced in 0.5.3, whereby a self referential relation from a base class to a joined-table subclass would not configure correctly.

- [orm]

  Fixed obscure mapper compilation issue when inheriting mappers are used which would result in un-initialized attributes.

- [orm]

  Fixed documentation for session weak_identity_map - the default value is True, indicating a weak referencing map in use.

- [orm]

  Fixed a unit of work issue whereby the foreign key attribute on an item contained within a collection owned by an object being deleted would not be set to None if the relation() was self-referential.

  References: #1376

- [orm]

  Fixed Query.update() and Query.delete() failures with eagerloaded relations.

  References: #1378

- [orm]

  It is now an error to specify both columns of a binary primaryjoin condition in the foreign_keys or remote_side collection. Whereas previously it was just nonsensical, but would succeed in a non-deterministic way.

### sql

- [sql]

  Back-ported the “compiler” extension from SQLA 0.6. This is a standardized interface which allows the creation of custom ClauseElement subclasses and compilers. In particular it’s handy as an alternative to text() when you’d like to build a construct that has database-specific compilations. See the extension docs for details.

- [sql]

  Exception messages are truncated when the list of bound parameters is larger than 10, preventing enormous multi-page exceptions from filling up screens and logfiles for large executemany() statements.

  References: #1413

- [sql]

  `sqlalchemy.extract()` is now dialect sensitive and can extract components of timestamps idiomatically across the supported databases, including SQLite.

- [sql]

  Fixed __repr__() and other _get_colspec() methods on ForeignKey constructed from __clause_element__() style construct (i.e. declarative columns).

  References: #1353

### schema

- [schema] [1341] [ticket: 594]

  Added a quote_schema() method to the IdentifierPreparer class so that dialects can override how schemas get handled. This enables the MSSQL dialect to treat schemas as multipart identifiers, such as ‘database.owner’.

### extensions

- [extensions]

  Fixed adding of deferred or other column properties to a declarative class.

  References: #1379

### mysql

- [mysql]

  Reflecting a FOREIGN KEY construct will take into account a dotted schema.tablename combination, if the foreign key references a table in a remote schema.

  References: #1405

### sqlite

- [sqlite]

  Corrected the SLBoolean type so that it properly treats only 1 as True.

  References: #1402

- [sqlite]

  Corrected the float type so that it correctly maps to a SLFloat type when being reflected.

  References: #1273

### mssql

- [mssql]

  Modified how savepoint logic works to prevent it from stepping on non-savepoint oriented routines. Savepoint support is still very experimental.

- [mssql]

  Added in reserved words for MSSQL that covers version 2008 and all prior versions.

  References: #1310

- [mssql]

  Corrected problem with information schema not working with a binary collation based database. Cleaned up information schema since it is only used by mssql now.

  References: #1343

## 0.5.3

Released: Tue Mar 24 2009

### orm

- [orm]

  The “objects” argument to session.flush() is deprecated. State which represents the linkage between a parent and child object does not support “flushed” status on one side of the link and not the other, so supporting this operation leads to misleading results.

  References: #1315

- [orm]

  Query now implements __clause_element__() which produces its selectable, which means a Query instance can be accepted in many SQL expressions, including col.in_(query), union(query1, query2), select([foo]).select_from(query), etc.

- [orm]

  Query.join() can now construct multiple FROM clauses, if needed. Such as, query(A, B).join(A.x).join(B.y) might say SELECT A.*, B.* FROM A JOIN X, B JOIN Y. Eager loading can also tack its joins onto those multiple FROM clauses.

  References: #1337

- [orm]

  Fixed bug in dynamic_loader() where append/remove events after construction time were not being propagated to the UOW to pick up on flush().

  References: #1347

- [orm]

  Fixed bug where column_prefix wasn’t being checked before not mapping an attribute that already had class-level name present.

- [orm]

  a session.expire() on a particular collection attribute will clear any pending backref additions as well, so that the next access correctly returns only what was present in the database. Presents some degree of a workaround for, although we are considering removing the flush([objects]) feature altogether.

  References: #1315

- [orm]

  Session.scalar() now converts raw SQL strings to text() the same way Session.execute() does and accepts same alternative **kw args.

- [orm]

  improvements to the “determine direction” logic of relation() such that the direction of tricky situations like mapper(A.join(B)) -> relation-> mapper(B) can be determined.

- [orm]

  When flushing partial sets of objects using session.flush([somelist]), pending objects which remain pending after the operation won’t inadvertently be added as persistent.

  References: #1306

- [orm]

  Added “post_configure_attribute” method to InstrumentationManager, so that the “listen_for_events.py” example works again.

  References: #1314

- [orm]

  a forward and complementing backwards reference which are both of the same direction, i.e. ONETOMANY or MANYTOONE, is now detected, and an error message is raised. Saves crazy CircularDependencyErrors later on.

- [orm]

  Fixed bugs in Query regarding simultaneous selection of multiple joined-table inheritance entities with common base classes:

  - previously the adaption applied to “B” on “A JOIN B” would be erroneously partially applied to “A”.

  - comparisons on relations (i.e. A.related==someb) were not getting adapted when they should.

  - Other filterings, like query(A).join(A.bs).filter(B.foo==’bar’), were erroneously adapting “B.foo” as though it were an “A”.

- [orm]

  Fixed adaptation of EXISTS clauses via any(), has(), etc. in conjunction with an aliased object on the left and of_type() on the right.

  References: #1325

- [orm]

  Added an attribute helper method `set_committed_value` in sqlalchemy.orm.attributes. Given an object, attribute name, and value, will set the value on the object as part of its “committed” state, i.e. state that is understood to have been loaded from the database. Helps with the creation of homegrown collection loaders and such.

- [orm]

  Query won’t fail with weakref error when a non-mapper/class instrumented descriptor is passed, raises “Invalid column expression”.

- [orm]

  Query.group_by() properly takes into account aliasing applied to the FROM clause, such as with select_from(), using with_polymorphic(), or using from_self().

### sql

- [sql]

  An alias() of a select() will convert to a “scalar subquery” when used in an unambiguously scalar context, i.e. it’s used in a comparison operation. This applies to the ORM when using query.subquery() as well.

- [sql]

  Fixed missing _label attribute on Function object, others when used in a select() with use_labels (such as when used in an ORM column_property()).

  References: #1302

- [sql]

  anonymous alias names now truncate down to the max length allowed by the dialect. More significant on DBs like Oracle with very small character limits.

  References: #1309

- [sql]

  the __selectable__() interface has been replaced entirely by __clause_element__().

- [sql]

  The per-dialect cache used by TypeEngine to cache dialect-specific types is now a WeakKeyDictionary. This to prevent dialect objects from being referenced forever for an application that creates an arbitrarily large number of engines or dialects. There is a small performance penalty which will be resolved in 0.6.

  References: #1299

### extensions

- [extensions]

  Fixed a recursive pickling issue in serializer, triggered by an EXISTS or other embedded FROM construct.

- [extensions]

  Declarative locates the “inherits” class using a search through __bases__, to skip over mixins that are local to subclasses.

- [extensions]

  Declarative figures out joined-table inheritance primary join condition even if “inherits” mapper argument is given explicitly.

- [extensions]

  Declarative will properly interpret the “foreign_keys” argument on a backref() if it’s a string.

- [extensions]

  Declarative will accept a table-bound column as a property when used in conjunction with __table__, if the column is already present in __table__. The column will be remapped to the given key the same way as when added to the mapper() properties dict.

### postgresql

- [postgresql]

  Index reflection won’t fail when an index with multiple expressions is encountered.

- [postgresql]

  Added PGUuid and PGBit types to sqlalchemy.databases.postgres.

  References: #1327

- [postgresql]

  Refection of unknown PG types won’t crash when those types are specified within a domain.

  References: #1327

### sqlite

- [sqlite]

  Fixed SQLite reflection methods so that non-present cursor.description, which triggers an auto-cursor close, will be detected so that no results doesn’t fail on recent versions of pysqlite which raise an error when fetchone() called with no rows present.

### mssql

- [mssql]

  Preliminary support for pymssql 1.0.1

- [mssql]

  Corrected issue on mssql where max_identifier_length was not being respected.

## 0.5.2

Released: Sat Jan 24 2009

### orm

- [orm]

  Further refined 0.5.1’s warning about delete-orphan cascade placed on a many-to-many relation. First, the bad news: the warning will apply to both many-to-many as well as many-to-one relations. This is necessary since in both cases, SQLA does not scan the full set of potential parents when determining “orphan” status - for a persistent object it only detects an in-python de-association event to establish the object as an “orphan”. Next, the good news: to support one-to-one via a foreign key or association table, or to support one-to-many via an association table, a new flag single_parent=True may be set which indicates objects linked to the relation are only meant to have a single parent. The relation will raise an error if multiple parent-association events occur within Python.

- [orm]

  Adjusted the attribute instrumentation change from 0.5.1 to fully establish instrumentation for subclasses where the mapper was created after the superclass had already been fully instrumented.

  References: #1292

- [orm]

  Fixed bug in delete-orphan cascade whereby two one-to-one relations from two different parent classes to the same target class would prematurely expunge the instance.

- [orm]

  Fixed an eager loading bug whereby self-referential eager loading would prevent other eager loads, self referential or not, from joining to the parent JOIN properly. Thanks to Alex K for creating a great test case.

- [orm]

  session.expire() and related methods will not expire() unloaded deferred attributes. This prevents them from being needlessly loaded when the instance is refreshed.

- [orm]

  query.join()/outerjoin() will now properly join an aliased() construct to the existing left side, even if query.from_self() or query.select_from(someselectable) has been called.

  References: #1293

### sql

- [sql]

  Further fixes to the “percent signs and spaces in column/table

    names” functionality.

  References: #1284

### mssql

- [mssql]

  Restored convert_unicode handling. Results were being passed on through without conversion.

  References: #1291

- [mssql]

  Really fixing the decimal handling this time..

  References: #1282

- [mssql] [Ticket:1289]

  Modified table reflection code to use only kwargs when constructing tables.

## 0.5.1

Released: Sat Jan 17 2009

### orm

- [orm]

  Removed an internal join cache which could potentially leak memory when issuing query.join() repeatedly to ad-hoc selectables.

- [orm]

  The “clear()”, “save()”, “update()”, “save_or_update()” Session methods have been deprecated, replaced by “expunge_all()” and “add()”. “expunge_all()” has also been added to ScopedSession.

- [orm]

  Modernized the “no mapped table” exception and added a more explicit __table__/__tablename__ exception to declarative.

- [orm]

  Concrete inheriting mappers now instrument attributes which are inherited from the superclass, but are not defined for the concrete mapper itself, with an InstrumentedAttribute that issues a descriptive error when accessed.

  References: #1237

- [orm]

  Added a new relation() keyword back_populates. This allows configuration of backreferences using explicit relations. This is required when creating bidirectional relations between a hierarchy of concrete mappers and another class.

  References: #1237, #781

- [orm]

  Test coverage added for relation() objects specified on concrete mappers.

  References: #1237

- [orm]

  Query.from_self() as well as query.subquery() both disable the rendering of eager joins inside the subquery produced. The “disable all eager joins” feature is available publicly via a new query.enable_eagerloads() generative.

  References: #1276

- [orm]

  Added a rudimental series of set operations to Query that receive Query objects as arguments, including union(), union_all(), intersect(), except_(), intersect_all(), except_all(). See the API documentation for Query.union() for examples.

- [orm]

  Fixed bug that prevented Query.join() and eagerloads from attaching to a query that selected from a union or aliased union.

- [orm]

  A short documentation example added for bidirectional relations specified on concrete mappers.

  References: #1237

- [orm]

  Mappers now instrument class attributes upon construction with the final InstrumentedAttribute object which remains persistent. The _CompileOnAttr/__getattribute__() methodology has been removed. The net effect is that Column-based mapped class attributes can now be used fully at the class level without invoking a mapper compilation operation, greatly simplifying typical usage patterns within declarative.

  References: #1269

- [orm]

  ColumnProperty (and front-end helpers such as `deferred`) no longer ignores unknown **keyword arguments.

- [orm]

  Fixed a bug with the unitofwork’s “row switch” mechanism, i.e. the conversion of INSERT/DELETE into an UPDATE, when combined with joined-table inheritance and an object which contained no defined values for the child table where an UPDATE with no SET clause would be rendered.

- [orm]

  Using delete-orphan on a many-to-many relation is deprecated. This produces misleading or erroneous results since SQLA does not retrieve the full list of “parents” for m2m. To get delete-orphan behavior with an m2m table, use an explicit association class so that the individual association row is treated as a parent.

  References: #1281

- [orm]

  delete-orphan cascade always requires delete cascade. Specifying delete-orphan without delete now raises a deprecation warning.

  References: #1281

### sql

- [sql]

  Improved the methodology to handling percent signs in column names from. Added more tests. MySQL and PostgreSQL dialects still do not issue correct CREATE TABLE statements for identifiers with percent signs in them.

  References: #1256

### schema

- [schema]

  Index now accepts column-oriented InstrumentedAttributes (i.e. column-based mapped class attributes) as column arguments.

  References: #1214

- [schema]

  Column with no name (as in declarative) won’t raise a NoneType error when its string output is requested (such as in a stack trace).

- [schema]

  Fixed bug when overriding a Column with a ForeignKey on a reflected table, where derived columns (i.e. the “virtual” columns of a select, etc.) would inadvertently call upon schema-level cleanup logic intended only for the original column.

  References: #1278

### mysql

- [mysql]

  Added the missing keywords from MySQL 4.1 so they get escaped properly.

### mssql

- [mssql]

  Corrected handling of large decimal values with more robust tests. Removed string manipulation on floats.

  References: #1280

- [mssql]

  Modified the do_begin handling in mssql to use the Cursor not the Connection so it is DBAPI compatible.

- [mssql]

  Corrected SAVEPOINT support on adodbapi by changing the handling of savepoint_release, which is unsupported on mssql.

### misc

- [declarative]

  Can now specify Column objects on subclasses which have no table of their own (i.e. use single table inheritance). The columns will be appended to the base table, but only mapped by the subclass.

- [declarative]

  For both joined and single inheriting subclasses, the subclass will only map those columns which are already mapped on the superclass and those explicit on the subclass. Other columns that are present on the Table will be excluded from the mapping by default, which can be disabled by passing a blank exclude_properties collection to the __mapper_args__. This is so that single-inheriting classes which define their own columns are the only classes to map those columns. The effect is actually a more organized mapping than you’d normally get with explicit mapper() calls unless you set up the exclude_properties arguments explicitly.

- [declarative]

  It’s an error to add new Column objects to a declarative class that specified an existing table using __table__.

## 0.5.0

Released: Tue Jan 06 2009

### general

- [general]

  Documentation has been converted to Sphinx. In particular, the generated API documentation has been constructed into a full blown “API Reference” section which organizes editorial documentation combined with generated docstrings. Cross linking between sections and API docs are vastly improved, a javascript-powered search feature is provided, and a full index of all classes, functions and members is provided.

- [general]

  setup.py now imports setuptools only optionally. If not present, distutils is used. The new “pip” installer is recommended over easy_install as it installs in a more simplified way.

- [general]

  added an extremely basic illustration of a PostGIS integration to the examples folder.

### orm

- [orm]

  Query.with_polymorphic() now accepts a third argument “discriminator” which will replace the value of mapper.polymorphic_on for that query. Mappers themselves no longer require polymorphic_on to be set, even if the mapper has a polymorphic_identity. When not set, the mapper will load non-polymorphically by default. Together, these two features allow a non-polymorphic concrete inheritance setup to use polymorphic loading on a per-query basis, since concrete setups are prone to many issues when used polymorphically in all cases.

- [orm]

  dynamic_loader accepts a query_class= to customize the Query classes used for both the dynamic collection and the queries built from it.

- [orm]

  query.order_by() accepts None which will remove any pending order_by state from the query, as well as cancel out any mapper/relation configured ordering. This is primarily useful for overriding the ordering specified on a dynamic_loader().

  References: #1079

- [orm]

  Exceptions raised during compile_mappers() are now preserved to provide “sticky behavior” - if a hasattr() call on a pre-compiled mapped attribute triggers a failing compile and suppresses the exception, subsequent compilation is blocked and the exception will be reiterated on the next compile() call. This issue occurs frequently when using declarative.

- [orm]

  property.of_type() is now recognized on a single-table inheriting target, when used in the context of prop.of_type(..).any()/has(), as well as query.join(prop.of_type(…)).

- [orm]

  query.join() raises an error when the target of the join doesn’t match the property-based attribute - while it’s unlikely anyone is doing this, the SQLAlchemy author was guilty of this particular loosey-goosey behavior.

- [orm]

  Fixed bug when using weak_instance_map=False where modified events would not be intercepted for a flush().

  References: #1272

- [orm]

  Fixed some deep “column correspondence” issues which could impact a Query made against a selectable containing multiple versions of the same table, as well as unions and similar which contained the same table columns in different column positions at different levels.

  References: #1268

- [orm]

  Custom comparator classes used in conjunction with column_property(), relation() etc. can define new comparison methods on the Comparator, which will become available via __getattr__() on the InstrumentedAttribute. In the case of synonym() or comparable_property(), attributes are resolved first on the user-defined descriptor, then on the user-defined comparator.

- [orm]

  Added ScopedSession.is_active accessor.

  References: #976

- [orm]

  Can pass mapped attributes and column objects as keys to query.update({}).

  References: #1262

- [orm]

  Mapped attributes passed to the values() of an expression level insert() or update() will use the keys of the mapped columns, not that of the mapped attribute.

- [orm]

  Corrected problem with Query.delete() and Query.update() not working properly with bind parameters.

  References: #1242

- [orm]

  Query.select_from(), from_statement() ensure that the given argument is a FromClause, or Text/Select/Union, respectively.

- [orm]

  Query() can be passed a “composite” attribute as a column expression and it will be expanded. Somewhat related to.

  References: #1253

- [orm]

  Query() is a little more robust when passed various column expressions such as strings, clauselists, text() constructs (which may mean it just raises an error more nicely).

- [orm]

  first() works as expected with Query.from_statement().

- [orm]

  Fixed bug introduced in 0.5rc4 involving eager loading not functioning for properties which were added to a mapper post-compile using add_property() or equivalent.

- [orm]

  Fixed bug where many-to-many relation() with viewonly=True would not correctly reference the link between secondary->remote.

- [orm]

  Duplicate items in a list-based collection will be maintained when issuing INSERTs to a “secondary” table in a many-to-many relation. Assuming the m2m table has a unique or primary key constraint on it, this will raise the expected constraint violation instead of silently dropping the duplicate entries. Note that the old behavior remains for a one-to-many relation since collection entries in that case don’t result in INSERT statements and SQLA doesn’t manually police collections.

  References: #1232

- [orm]

  Query.add_column() can accept FromClause objects in the same manner as session.query() can.

- [orm]

  Comparison of many-to-one relation to NULL is properly converted to IS NOT NULL based on not_().

- [orm]

  Extra checks added to ensure explicit primaryjoin/secondaryjoin are ClauseElement instances, to prevent more confusing errors later on.

  References: #1087

- [orm]

  Improved mapper() check for non-class classes.

  References: #1236

- [orm]

  comparator_factory argument is now documented and supported by all MapperProperty types, including column_property(), relation(), backref(), and synonym().

  References: #5051

- [orm]

  Changed the name of PropertyLoader to RelationProperty, to be consistent with all the other names. PropertyLoader is still present as a synonym.

- [orm]

  fixed “double iter()” call causing bus errors in shard API, removed errant result.close() left over from the 0.4 version.

  References: #1099, #1228

- [orm]

  made Session.merge cascades not trigger autoflush. Fixes merged instances getting prematurely inserted with missing values.

- [orm]

  Two fixes to help prevent out-of-band columns from being rendered in polymorphic_union inheritance scenarios (which then causes extra tables to be rendered in the FROM clause causing cartesian products):

  > - improvements to “column adaption” for a->b->c inheritance situations to better locate columns that are related to one another via multiple levels of indirection, rather than rendering the non-adapted column.

  > - the “polymorphic discriminator” column is only rendered for the actual mapper being queried against. The column won’t be “pulled in” from a subclass or superclass mapper since it’s not needed.

- [orm]

  Fixed shard_id argument on ShardedSession.execute().

  References: #1072

### sql

- [sql]

  RowProxy objects can be used in place of dictionary arguments sent to connection.execute() and friends.

  References: #935

- [sql]

  Columns can again contain percent signs within their names.

  References: #1256

- [sql]

  sqlalchemy.sql.expression.Function is now a public class. It can be subclassed to provide user-defined SQL functions in an imperative style, including with pre-established behaviors. The postgis.py example illustrates one usage of this.

- [sql]

  PickleType now favors == comparison by default, if the incoming object (such as a dict) implements __eq__(). If the object does not implement __eq__() and mutable=True, a deprecation warning is raised.

- [sql]

  Fixed the import weirdness in sqlalchemy.sql to not export __names__.

  References: #1215

- [sql]

  Using the same ForeignKey object repeatedly raises an error instead of silently failing later.

  References: #1238

- [sql]

  Added NotImplementedError for params() method on Insert/Update/Delete constructs. These items currently don’t support this functionality, which also would be a little misleading compared to values().

- [sql]

  Reflected foreign keys will properly locate their referenced column, even if the column was given a “key” attribute different from the reflected name. This is achieved via a new flag on ForeignKey/ForeignKeyConstraint called “link_to_name”, if True means the given name is the referred-to column’s name, not its assigned key.

  References: #650

- [sql]

  select() can accept a ClauseList as a column in the same way as a Table or other selectable and the interior expressions will be used as column elements.

  References: #1253

- [sql]

  the “passive” flag on session.is_modified() is correctly propagated to the attribute manager.

- [sql]

  union() and union_all() will not whack any order_by() that has been applied to the select()s inside. If you union() a select() with order_by() (presumably to support LIMIT/OFFSET), you should also call self_group() on it to apply parenthesis.

### mysql

- [mysql]

  ”%” signs in text() constructs are automatically escaped to “%%”. Because of the backwards incompatible nature of this change, a warning is emitted if ‘%%’ is detected in the string.

- [mysql]

  Fixed bug in exception raise when FK columns not present during reflection.

  References: #1241

- [mysql]

  Fixed bug involving reflection of a remote-schema table with a foreign key ref to another table in that schema.

### sqlite

- [sqlite]

  Table reflection now stores the actual DefaultClause value for the column.

  References: #1266

- [sqlite]

  bugfixes, behavioral changes

### mssql

- [mssql]

  Added in a new MSGenericBinary type. This maps to the Binary type so it can implement the specialized behavior of treating length specified types as fixed-width Binary types and non-length types as an unbound variable length Binary type.

- [mssql]

  Added in new types: MSVarBinary and MSImage.

  References: #1249

- [mssql]

  Added in the MSReal, MSNText, MSSmallDateTime, MSTime, MSDateTimeOffset, and MSDateTime2 types

- [mssql]

  Refactored the Date/Time types. The `smalldatetime` data type no longer truncates to a date only, and will now be mapped to the MSSmallDateTime type.

  References: #1254

- [mssql]

  Corrected an issue with Numerics to accept an int.

- [mssql]

  Mapped `char_length` to the `LEN()` function.

- [mssql]

  If an `INSERT` includes a subselect the `INSERT` is converted from an `INSERT INTO VALUES` construct to a `INSERT INTO SELECT` construct.

- [mssql]

  If the column is part of a `primary_key` it will be `NOT NULL` since MSSQL doesn’t allow `NULL` in primary_key columns.

- [mssql]

  `MSBinary` now returns a `BINARY` instead of an `IMAGE`. This is a backwards incompatible change in that `BINARY` is a fixed length data type whereas `IMAGE` is a variable length data type.

  References: #1249

- [mssql]

  `get_default_schema_name` is now reflected from the database based on the user’s default schema. This only works with MSSQL 2005 and later.

  References: #1258

- [mssql]

  Added collation support through the use of a new collation argument. This is supported on the following types: char, nchar, varchar, nvarchar, text, ntext.

  References: #1248

- [mssql]

  Changes to the connection string parameters favor DSN as the default specification for pyodbc. See the mssql.py docstring for detailed usage instructions.

- [mssql]

  Added experimental support of savepoints. It currently does not work fully with sessions.

- [mssql]

  Support for three levels of column nullability: NULL, NOT NULL, and the database’s configured default. The default Column configuration (nullable=True) will now generate NULL in the DDL. Previously no specification was emitted and the database default would take effect (usually NULL, but not always). To explicitly request the database default, configure columns with nullable=None and no specification will be emitted in DDL. This is backwards incompatible behavior.

  References: #1243

### oracle

- [oracle]

  Adjusted the format of create_xid() to repair two-phase commit. We now have field reports of Oracle two-phase commit working properly with this change.

- [oracle]

  Added OracleNVarchar type, produces NVARCHAR2, and also subclasses Unicode so that convert_unicode=True by default. NVARCHAR2 reflects into this type automatically so these columns pass unicode on a reflected table with no explicit convert_unicode=True flags.

  References: #1233

- [oracle]

  Fixed bug which was preventing out params of certain types from being received; thanks a ton to huddlej at wwu.edu !

  References: #1265

### misc

- [dialect]

  Added a new description_encoding attribute on the dialect that is used for encoding the column name when processing the metadata. This usually defaults to utf-8.

- [engine/pool]

  Connection.invalidate() checks for closed status to avoid attribute errors.

  References: #1246

- [engine/pool]

  NullPool supports reconnect on failure behavior.

  References: #1094

- [engine/pool]

  Added a mutex for the initial pool creation when using pool.manage(dbapi). This prevents a minor case of “dogpile” behavior which would otherwise occur upon a heavy load startup.

  References: #799

- [engine/pool]

  _execute_clauseelement() goes back to being a private method. Subclassing Connection is not needed now that ConnectionProxy is available.

- [documentation]

  Tickets.

  References: #1149, #1200

- [documentation]

  Added note about create_session() defaults.

- [documentation]

  Added section about metadata.reflect().

- [documentation]

  Updated TypeDecorator section.

- [documentation]

  Rewrote the “threadlocal” strategy section of the docs due to recent confusion over this feature.

- [documentation]

  Removed badly out of date ‘polymorphic_fetch’ and ‘select_table’ docs from inheritance, reworked the second half of “joined table inheritance”.

- [documentation]

  Documented comparator_factory kwarg, added new doc section “Custom Comparators”.

- [postgres]

  ”%” signs in text() constructs are automatically escaped to “%%”. Because of the backwards incompatible nature of this change, a warning is emitted if ‘%%’ is detected in the string.

  References: #1267

- [postgres]

  Calling alias.execute() in conjunction with server_side_cursors won’t raise AttributeError.

- [postgres]

  Added Index reflection support to PostgreSQL, using a great patch we long neglected, submitted by Ken Kuhlman.

  References: #714

- [associationproxy]

  The association proxy properties are make themselves available at the class level, e.g. MyClass.aproxy. Previously this evaluated to None.

- [declarative]

  The full list of arguments accepted as string by backref() includes ‘primaryjoin’, ‘secondaryjoin’, ‘secondary’, ‘foreign_keys’, ‘remote_side’, ‘order_by’.

## 0.5.0rc4

Released: Fri Nov 14 2008

### general

- [general]

  global “propigate”->”propagate” change.

### orm

- [orm]

  Query.count() has been enhanced to do the “right thing” in a wider variety of cases. It can now count multiple-entity queries, as well as column-based queries. Note that this means if you say query(A, B).count() without any joining criterion, it’s going to count the cartesian product of A*B. Any query which is against column-based entities will automatically issue “SELECT count(1) FROM (SELECT…)” so that the real rowcount is returned, meaning a query such as query(func.count(A.name)).count() will return a value of one, since that query would return one row.

- [orm]

  Lots of performance tuning. A rough guesstimate over various ORM operations places it 10% faster over 0.5.0rc3, 25-30% over 0.4.8.

- [orm]

  bugfixes and behavioral changes

- [orm]

  Adjustments to the enhanced garbage collection on InstanceState to better guard against errors due to lost state.

- [orm]

  Query.get() returns a more informative error message when executed against multiple entities.

  References: #1220

- [orm]

  Restored NotImplementedError on Cls.relation.in_()

  References: #1140, #1221

- [orm]

  Fixed PendingDeprecationWarning involving order_by parameter on relation().

  References: #1226

### sql

- [sql]

  Removed the ‘properties’ attribute of the Connection object, Connection.info should be used.

- [sql]

  Restored “active rowcount” fetch before ResultProxy autocloses the cursor. This was removed in 0.5rc3.

- [sql]

  Rearranged the load_dialect_impl() method in TypeDecorator such that it will take effect even if the user-defined TypeDecorator uses another TypeDecorator as its impl.

### mssql

- [mssql]

  Lots of cleanup and fixes to correct problems with limit and offset.

- [mssql]

  Correct situation where subqueries as part of a binary expression need to be translated to use the IN and NOT IN syntax.

- [mssql]

  Fixed E Notation issue that prevented the ability to insert decimal values less than 1E-6.

  References: #1216

- [mssql]

  Corrected problems with reflection when dealing with schemas, particularly when those schemas are the default schema.

  References: #1217

- [mssql]

  Corrected problem with casting a zero length item to a varchar. It now correctly adjusts the CAST.

### misc

- [access]

  Added support for Currency type.

- [access]

  Functions were not return their result.

  References: #1017

- [access]

  Corrected problem with joins. Access only support LEFT OUTER or INNER not just JOIN by itself.

  References: #1017

- [ext]

  Can now use a custom “inherit_condition” in __mapper_args__ when using declarative.

- [ext]

  fixed string-based “remote_side”, “order_by” and others not propagating correctly when used in backref().

## 0.5.0rc3

Released: Fri Nov 07 2008

### orm

- [orm]

  Added two new hooks to SessionExtension: after_bulk_delete() and after_bulk_update(). after_bulk_delete() is called after a bulk delete() operation on a query. after_bulk_update() is called after a bulk update() operation on a query.

- [orm]

  ”not equals” comparisons of simple many-to-one relation to an instance will not drop into an EXISTS clause and will compare foreign key columns instead.

- [orm]

  Removed not-really-working use cases of comparing a collection to an iterable. Use contains() to test for collection membership.

- [orm]

  Improved the behavior of aliased() objects such that they more accurately adapt the expressions generated, which helps particularly with self-referential comparisons.

  References: #1171

- [orm]

  Fixed bug involving primaryjoin/secondaryjoin conditions constructed from class-bound attributes (as often occurs when using declarative), which later would be inappropriately aliased by Query, particularly with the various EXISTS based comparators.

- [orm]

  Fixed bug when using multiple query.join() with an aliased-bound descriptor which would lose the left alias.

- [orm]

  Improved weakref identity map memory management to no longer require mutexing, resurrects garbage collected instance on a lazy basis for an InstanceState with pending changes.

- [orm]

  InstanceState object now removes circular references to itself upon disposal to keep it outside of cyclic garbage collection.

- [orm]

  relation() won’t hide unrelated ForeignKey errors inside of the “please specify primaryjoin” message when determining join condition.

- [orm]

  Fixed bug in Query involving order_by() in conjunction with multiple aliases of the same class (will add tests in)

  References: #1218

- [orm]

  When using Query.join() with an explicit clause for the ON clause, the clause will be aliased in terms of the left side of the join, allowing scenarios like query(Source). from_self().join((Dest, Source.id==Dest.source_id)) to work properly.

- [orm]

  polymorphic_union() function respects the “key” of each Column if they differ from the column’s name.

- [orm]

  Repaired support for “passive-deletes” on a many-to-one relation() with “delete” cascade.

  References: #1183

- [orm]

  Fixed bug in composite types which prevented a primary-key composite type from being mutated.

  References: #1213

- [orm]

  Added more granularity to internal attribute access, such that cascade and flush operations will not initialize unloaded attributes and collections, leaving them intact for a lazy-load later on. Backref events still initialize attributes and collections for pending instances.

  References: #1202

### sql

- [sql]

  SQL compiler optimizations and complexity reduction. The call count for compiling a typical select() construct is 20% less versus 0.5.0rc2.

- [sql]

  Dialects can now generate label names of adjustable length. Pass in the argument “label_length=<value>” to create_engine() to adjust how many characters max will be present in dynamically generated column labels, i.e. “somecolumn AS somelabel”. Any value less than 6 will result in a label of minimal size, consisting of an underscore and a numeric counter. The compiler uses the value of dialect.max_identifier_length as a default.

  References: #1211

- [sql]

  Simplified the check for ResultProxy “autoclose without results” to be based solely on presence of cursor.description. All the regexp-based guessing about statements returning rows has been removed.

  References: #1212

- [sql]

  Direct execution of a union() construct will properly set up result-row processing.

  References: #1194

- [sql]

  The internal notion of an “OID” or “ROWID” column has been removed. It’s basically not used by any dialect, and the possibility of its usage with psycopg2’s cursor.lastrowid is basically gone now that INSERT..RETURNING is available.

- [sql]

  Removed “default_order_by()” method on all FromClause objects.

- [sql]

  Repaired the table.tometadata() method so that a passed-in schema argument is propagated to ForeignKey constructs.

- [sql]

  Slightly changed behavior of IN operator for comparing to empty collections. Now results in inequality comparison against self. More portable, but breaks with stored procedures that aren’t pure functions.

### mysql

- [mysql]

  Fixed foreign key reflection in the edge case where a Table’s explicit schema= is the same as the schema (database) the connection is attached to.

- [mysql]

  No longer expects include_columns in table reflection to be lower case.

### oracle

- [oracle]

  Wrote a docstring for Oracle dialect. Apparently that Ohloh “few source code comments” label is starting to string :).

- [oracle]

  Removed FIRST_ROWS() optimize flag when using LIMIT/OFFSET, can be re-enabled with optimize_limits=True create_engine() flag.

  References: #536

- [oracle]

  bugfixes and behavioral changes

- [oracle]

  Setting the auto_convert_lobs to False on create_engine() will also instruct the OracleBinary type to return the cx_oracle LOB object unchanged.

### misc

- [ext]

  Added a new extension sqlalchemy.ext.serializer. Provides Serializer/Deserializer “classes” which mirror Pickle/Unpickle, as well as dumps() and loads(). This serializer implements an “external object” pickler which keeps key context-sensitive objects, including engines, sessions, metadata, Tables/Columns, and mappers, outside of the pickle stream, and can later restore the pickle using any engine/metadata/session provider. This is used not for pickling regular object instances, which are pickleable without any special logic, but for pickling expression objects and full Query objects, such that all mapper/engine/session dependencies can be restored at unpickle time.

- [ext]

  Fixed bug preventing declarative-bound “column” objects from being used in column_mapped_collection().

  References: #1174

- [misc]

  util.flatten_iterator() func doesn’t interpret strings with __iter__() methods as iterators, such as in pypy.

  References: #1077

## 0.5.0rc2

Released: Sun Oct 12 2008

### orm

- [orm]

  Fixed bug involving read/write relation()s that contain literal or other non-column expressions within their primaryjoin condition equated to a foreign key column.

- [orm]

  ”non-batch” mode in mapper(), a feature which allows mapper extension methods to be called as each instance is updated/inserted, now honors the insert order of the objects given.

- [orm]

  Fixed RLock-related bug in mapper which could deadlock upon reentrant mapper compile() calls, something that occurs when using declarative constructs inside of ForeignKey objects.

- [orm]

  ScopedSession.query_property now accepts a query_cls factory, overriding the session’s configured query_cls.

- [orm]

  Fixed shared state bug interfering with ScopedSession.mapper’s ability to apply default __init__ implementations on object subclasses.

- [orm]

  Fixed up slices on Query (i.e. query[x:y]) to work properly for zero length slices, slices with None on either end.

  References: #1177

- [orm]

  Added an example illustrating Celko’s “nested sets” as a SQLA mapping.

- [orm]

  contains_eager() with an alias argument works even when the alias is embedded in a SELECT, as when sent to the Query via query.select_from().

- [orm]

  contains_eager() usage is now compatible with a Query that also contains a regular eager load and limit/offset, in that the columns are added to the Query-generated subquery.

  References: #1180

- [orm]

  session.execute() will execute a Sequence object passed to it (regression from 0.4).

- [orm]

  Removed the “raiseerror” keyword argument from object_mapper() and class_mapper(). These functions raise in all cases if the given class/instance is not mapped.

- [orm]

  Fixed session.transaction.commit() on a autocommit=False session not starting a new transaction.

- [orm]

  Some adjustments to Session.identity_map’s weak referencing behavior to reduce asynchronous GC side effects.

- [orm]

  Adjustment to Session’s post-flush accounting of newly “clean” objects to better protect against operating on objects as they’re asynchronously gc’ed.

  References: #1182

### sql

- [sql]

  column.in_(someselect) can now be used as a columns-clause expression without the subquery bleeding into the FROM clause

  References: #1074

### mysql

- [mysql]

  Temporary tables are now reflectable.

### sqlite

- [sqlite]

  Overhauled SQLite date/time bind/result processing to use regular expressions and format strings, rather than strptime/strftime, to generically support pre-1900 dates, dates with microseconds.

  References: #968

- [sqlite]

  String’s (and Unicode’s, UnicodeText’s, etc.) convert_unicode logic disabled in the sqlite dialect, to adjust for pysqlite 2.5.0’s new requirement that only Python unicode objects are accepted; http://web.archive.org/web/20090614054912/https://itsystementwicklung.de/pipermail/list-pysqlite/2008-March/000018.html

### oracle

- [oracle]

  Oracle will detect string-based statements which contain comments at the front before a SELECT as SELECT statements.

  References: #1187

## 0.5.0rc1

Released: Thu Sep 11 2008

### orm

- [orm]

  Query now has delete() and update(values) methods. This allows to perform bulk deletes/updates with the Query object.

- [orm]

  The RowTuple object returned by Query(*cols) now features keynames which prefer mapped attribute names over column keys, column keys over column names, i.e. Query(Class.foo, Class.bar) will have names “foo” and “bar” even if those are not the names of the underlying Column objects. Direct Column objects such as Query(table.c.col) will return the “key” attribute of the Column.

- [orm]

  Added scalar() and value() methods to Query, each return a single scalar value. scalar() takes no arguments and is roughly equivalent to first()[0], value() takes a single column expression and is roughly equivalent to values(expr).next()[0].

- [orm]

  Improved the determination of the FROM clause when placing SQL expressions in the query() list of entities. In particular scalar subqueries should not “leak” their inner FROM objects out into the enclosing query.

- [orm]

  Joins along a relation() from a mapped class to a mapped subclass, where the mapped subclass is configured with single table inheritance, will include an IN clause which limits the subtypes of the joined class to those requested, within the ON clause of the join. This takes effect for eager load joins as well as query.join(). Note that in some scenarios the IN clause will appear in the WHERE clause of the query as well since this discrimination has multiple trigger points.

- [orm]

  AttributeExtension has been refined such that the event is fired before the mutation actually occurs. Additionally, the append() and set() methods must now return the given value, which is used as the value to be used in the mutation operation. This allows creation of validating AttributeListeners which raise before the action actually occurs, and which can change the given value into something else before its used.

- [orm]

  column_property(), composite_property(), and relation() now accept a single or list of AttributeExtensions using the “extension” keyword argument.

- [orm]

  query.order_by().get() silently drops the “ORDER BY” from the query issued by GET but does not raise an exception.

- [orm]

  Added a Validator AttributeExtension, as well as a @validates decorator which is used in a similar fashion as @reconstructor, and marks a method as validating one or more mapped attributes.

- [orm]

  class.someprop.in_() raises NotImplementedError pending the implementation of “in_” for relation

  References: #1140

- [orm]

  Fixed primary key update for many-to-many collections where the collection had not been loaded yet

  References: #1127

- [orm]

  Fixed bug whereby deferred() columns with a group in conjunction with an otherwise unrelated synonym() would produce an AttributeError during deferred load.

- [orm]

  The before_flush() hook on SessionExtension takes place before the list of new/dirty/deleted is calculated for the final time, allowing routines within before_flush() to further change the state of the Session before the flush proceeds.

  References: #1128

- [orm]

  The “extension” argument to Session and others can now optionally be a list, supporting events sent to multiple SessionExtension instances. Session places SessionExtensions in Session.extensions.

- [orm]

  Reentrant calls to flush() raise an error. This also serves as a rudimentary, but not foolproof, check against concurrent calls to Session.flush().

- [orm]

  Improved the behavior of query.join() when joining to joined-table inheritance subclasses, using explicit join criteria (i.e. not on a relation).

- [orm]

  @orm.attributes.reconstitute and MapperExtension.reconstitute have been renamed to @orm.reconstructor and MapperExtension.reconstruct_instance

- [orm]

  Fixed @reconstructor hook for subclasses which inherit from a base class.

  References: #1129

- [orm]

  The composite() property type now supports a __set_composite_values__() method on the composite class which is required if the class represents state using attribute names other than the column’s keynames; default-generated values now get populated properly upon flush. Also, composites with attributes set to None compare correctly.

  References: #1132

- [orm]

  The 3-tuple of iterables returned by attributes.get_history() may now be a mix of lists and tuples. (Previously members were always lists.)

- [orm]

  Fixed bug whereby changing a primary key attribute on an entity where the attribute’s previous value had been expired would produce an error upon flush().

  References: #1151

- [orm]

  Fixed custom instrumentation bug whereby get_instance_dict() was not called for newly constructed instances not loaded by the ORM.

- [orm]

  Session.delete() adds the given object to the session if not already present. This was a regression bug from 0.4.

  References: #1150

- [orm]

  The echo_uow flag on Session is deprecated, and unit-of-work logging is now application-level only, not per-session level.

- [orm]

  Removed conflicting contains() operator from InstrumentedAttribute which didn’t accept escape kwaarg.

  References: #1153

### sql

- [sql]

  Temporarily rolled back the “ORDER BY” enhancement from. This feature is on hold pending further development.

  References: #1068

- [sql]

  The exists() construct won’t “export” its contained list of elements as FROM clauses, allowing them to be used more effectively in the columns clause of a SELECT.

- [sql]

  and_() and or_() now generate a ColumnElement, allowing boolean expressions as result columns, i.e. select([and_(1, 0)]).

  References: #798

- [sql]

  Bind params now subclass ColumnElement which allows them to be selectable by orm.query (they already had most ColumnElement semantics).

- [sql]

  Added select_from() method to exists() construct, which becomes more and more compatible with a regular select().

- [sql]

  Added func.min(), func.max(), func.sum() as “generic functions”, which basically allows for their return type to be determined automatically. Helps with dates on SQLite, decimal types, others.

  References: #1160

- [sql]

  added decimal.Decimal as an “auto-detect” type; bind parameters and generic functions will set their type to Numeric when a Decimal is used.

### schema

- [schema]

  Added “sorted_tables” accessor to MetaData, which returns Table objects sorted in order of dependency as a list. This deprecates the MetaData.table_iterator() method. The “reverse=False” keyword argument has also been removed from util.sort_tables(); use the Python ‘reversed’ function to reverse the results.

  References: #1033

- [schema]

  The ‘length’ argument to all Numeric types has been renamed to ‘scale’. ‘length’ is deprecated and is still accepted with a warning.

- [schema]

  Dropped 0.3-compatibility for user defined types (convert_result_value, convert_bind_param).

### mysql

- [mysql]

  The ‘length’ argument to MSInteger, MSBigInteger, MSTinyInteger, MSSmallInteger and MSYear has been renamed to ‘display_width’.

- [mysql]

  Added MSMediumInteger type.

  References: #1146

- [mysql]

  the function func.utc_timestamp() compiles to UTC_TIMESTAMP, without the parenthesis, which seem to get in the way when using in conjunction with executemany().

### oracle

- [oracle]

  limit/offset no longer uses ROW NUMBER OVER to limit rows, and instead uses subqueries in conjunction with a special Oracle optimization comment. Allows LIMIT/OFFSET to work in conjunction with DISTINCT.

  References: #536

- [oracle]

  has_sequence() now takes the current “schema” argument into account

  References: #1155

- [oracle]

  added BFILE to reflected type names

  References: #1121

### misc

- [declarative]

  Fixed bug whereby mapper couldn’t initialize if a composite primary key referenced another table that was not defined yet.

  References: #1161

- [declarative]

  Fixed exception throw which would occur when string-based primaryjoin condition was used in conjunction with backref.

## 0.5.0beta3

Released: Mon Aug 04 2008

### orm

- [orm]

  The “entity_name” feature of SQLAlchemy mappers has been removed. For rationale, see https://tinyurl.com/6nm2ne

- [orm]

  the “autoexpire” flag on Session, sessionmaker(), and scoped_session() has been renamed to “expire_on_commit”. It does not affect the expiration behavior of rollback().

- [orm]

  fixed endless loop bug which could occur within a mapper’s deferred load of inherited attributes.

- [orm]

  a legacy-support flag “_enable_transaction_accounting” flag added to Session which when False, disables all transaction-level object accounting, including expire on rollback, expire on commit, new/deleted list maintenance, and autoflush on begin.

- [orm]

  The ‘cascade’ parameter to relation() accepts None as a value, which is equivalent to no cascades.

- [orm]

  A critical fix to dynamic relations allows the “modified” history to be properly cleared after a flush().

- [orm]

  user-defined @properties on a class are detected and left in place during mapper initialization. This means that a table-bound column of the same name will not be mapped at all if a @property is in the way (and the column is not remapped to a different name), nor will an instrumented attribute from an inherited class be applied. The same rules apply for names excluded using the include_properties/exclude_properties collections.

- [orm]

  Added a new SessionExtension hook called after_attach(). This is called at the point of attachment for objects via add(), add_all(), delete(), and merge().

- [orm]

  A mapper which inherits from another, when inheriting the columns of its inherited mapper, will use any reassigned property names specified in that inheriting mapper. Previously, if “Base” had reassigned “base_id” to the name “id”, “SubBase(Base)” would still get an attribute called “base_id”. This could be worked around by explicitly stating the column in each submapper as well but this is fairly unworkable and also impossible when using declarative.

  References: #1111

- [orm]

  Fixed a series of potential race conditions in Session whereby asynchronous GC could remove unmodified, no longer referenced items from the session as they were present in a list of items to be processed, typically during session.expunge_all() and dependent methods.

- [orm]

  Some improvements to the _CompileOnAttr mechanism which should reduce the probability of “Attribute x was not replaced during compile” warnings. (this generally applies to SQLA hackers, like Elixir devs).

- [orm]

  Fixed bug whereby the “unsaved, pending instance” FlushError raised for a pending orphan would not take superclass mappers into account when generating the list of relations responsible for the error.

### sql

- [sql]

  func.count() with no arguments renders as COUNT(*), equivalent to func.count(text(‘*’)).

- [sql]

  simple label names in ORDER BY expressions render as themselves, and not as a re-statement of their corresponding expression. This feature is currently enabled only for SQLite, MySQL, and PostgreSQL. It can be enabled on other dialects as each is shown to support this behavior.

  References: #1068

### mysql

- [mysql]

  Quoting of MSEnum values for use in CREATE TABLE is now optional & will be quoted on demand as required. (Quoting was always optional for use with existing tables.)

  References: #1110

### misc

- [ext]

  Class-bound attributes sent as arguments to relation()’s remote_side and foreign_keys parameters are now accepted, allowing them to be used with declarative. Additionally fixed bugs involving order_by being specified as a class-bound attribute in conjunction with eager loading.

- [ext]

  declarative initialization of Columns adjusted so that non-renamed columns initialize in the same way as a non declarative mapper. This allows an inheriting mapper to set up its same-named “id” columns in particular such that the parent “id” column is favored over the child column, reducing database round trips when this value is requested.

## 0.5.0beta2

Released: Mon Jul 14 2008

### orm

- [orm]

  In addition to expired attributes, deferred attributes also load if their data is present in the result set.

  References: #870

- [orm]

  session.refresh() raises an informative error message if the list of attributes does not include any column-based attributes.

- [orm]

  query() raises an informative error message if no columns or mappers are specified.

- [orm]

  lazy loaders now trigger autoflush before proceeding. This allows expire() of a collection or scalar relation to function properly in the context of autoflush.

- [orm]

  column_property() attributes which represent SQL expressions or columns that are not present in the mapped tables (such as those from views) are automatically expired after an INSERT or UPDATE, assuming they have not been locally modified, so that they are refreshed with the most recent data upon access.

  References: #887

- [orm]

  Fixed explicit, self-referential joins between two joined-table inheritance mappers when using query.join(cls, aliased=True).

  References: #1082

- [orm]

  Fixed query.join() when used in conjunction with a columns-only clause and a SQL-expression ON clause in the join.

- [orm]

  The “allow_column_override” flag from mapper() has been removed. This flag is virtually always misunderstood. Its specific functionality is available via the include_properties/exclude_properties mapper arguments.

- [orm]

  Repaired __str__() method on Query.

  References: #1066

- [orm]

  Session.bind gets used as a default even when table/mapper specific binds are defined.

### sql

- [sql]

  Added new match() operator that performs a full-text search. Supported on PostgreSQL, SQLite, MySQL, MS-SQL, and Oracle backends.

### schema

- [schema]

  Added prefixes option to Table that accepts a list of strings to insert after CREATE in the CREATE TABLE statement.

  References: #1075

- [schema]

  Unicode, UnicodeText types now set “assert_unicode” and “convert_unicode” by default, but accept overriding **kwargs for these values.

### extensions

- [extensions]

  Declarative supports a __table_args__ class variable, which is either a dictionary, or tuple of the form (arg1, arg2, …, {kwarg1:value, …}) which contains positional + kw arguments to be passed to the Table constructor.

  References: #1096

### sqlite

- [sqlite]

  Modified SQLite’s representation of “microseconds” to match the output of str(somedatetime), i.e. in that the microseconds are represented as fractional seconds in string format. This makes SQLA’s SQLite date type compatible with datetimes that were saved directly using Pysqlite (which just calls str()). Note that this is incompatible with the existing microseconds values in a SQLA 0.4 generated SQLite database file.

  To get the old behavior globally:

  > from sqlalchemy.databases.sqlite import DateTimeMixin DateTimeMixin.__legacy_microseconds__ = True

  To get the behavior on individual DateTime types:

  > t = sqlite.SLDateTime() t.__legacy_microseconds__ = True

  Then use “t” as the type on the Column.

  References: #1090

- [sqlite]

  SQLite Date, DateTime, and Time types only accept Python datetime objects now, not strings. If you’d like to format dates as strings yourself with SQLite, use a String type. If you’d like them to return datetime objects anyway despite their accepting strings as input, make a TypeDecorator around String - SQLA doesn’t encourage this pattern.

## 0.5.0beta1

Released: Thu Jun 12 2008

### general

- [general]

  global “propigate”->”propagate” change.

### orm

- [orm]

  polymorphic_union() function respects the “key” of each Column if they differ from the column’s name.

- [orm]

  Fixed 0.4-only bug preventing composite columns from working properly with inheriting mappers

  References: #1199

- [orm]

  Fixed RLock-related bug in mapper which could deadlock upon reentrant mapper compile() calls, something that occurs when using declarative constructs inside of ForeignKey objects. Ported from 0.5.

- [orm]

  Fixed bug in composite types which prevented a primary-key composite type from being mutated.

  References: #1213

- [orm]

  Added ScopedSession.is_active accessor.

  References: #976

- [orm]

  Class-bound accessor can be used as the argument to relation() order_by.

  References: #939

- [orm]

  Fixed shard_id argument on ShardedSession.execute().

  References: #1072

### sql

- [sql]

  Connection.invalidate() checks for closed status to avoid attribute errors.

  References: #1246

- [sql]

  NullPool supports reconnect on failure behavior.

  References: #1094

- [sql]

  The per-dialect cache used by TypeEngine to cache dialect-specific types is now a WeakKeyDictionary. This to prevent dialect objects from being referenced forever for an application that creates an arbitrarily large number of engines or dialects. There is a small performance penalty which will be resolved in 0.6.

  References: #1299

- [sql]

  Fixed SQLite reflection methods so that non-present cursor.description, which triggers an auto-cursor close, will be detected so that no results doesn’t fail on recent versions of pysqlite which raise an error when fetchone() called with no rows present.

### mysql

- [mysql]

  Fixed bug in exception raise when FK columns not present during reflection.

  References: #1241

### oracle

- [oracle]

  Fixed bug which was preventing out params of certain types from being received; thanks a ton to huddlej at wwu.edu !

  References: #1265

### misc

- [no_tags]

  The “__init__” trigger/decorator added by mapper now attempts to exactly mirror the argument signature of the original __init__. The pass-through for ‘_sa_session’ is no longer implicit- you must allow for this keyword argument in your constructor.

- [no_tags]

  ClassState is renamed to ClassManager.

- [no_tags]

  Classes may supply their own InstrumentationManager by providing a __sa_instrumentation_manager__ property.

- [no_tags]

  Custom instrumentation may use any mechanism to associate a ClassManager with a class and an InstanceState with an instance. Attributes on those objects are still the default association mechanism used by SQLAlchemy’s native instrumentation.

- [no_tags]

  Moved entity_name, _sa_session_id, and _instance_key from the instance object to the instance state. These values are still available in the old way, which is now deprecated, using descriptors attached to the class. A deprecation warning will be issued when accessed.

- [no_tags]

  The _prepare_instrumentation alias for prepare_instrumentation has been removed.

- [no_tags]

  sqlalchemy.exceptions has been renamed to sqlalchemy.exc. The module may be imported under either name.

- [no_tags]

  ORM-related exceptions are now defined in sqlalchemy.orm.exc. ConcurrentModificationError, FlushError, and UnmappedColumnError compatibility aliases are installed in sqlalchemy.exc during the import of sqlalchemy.orm.

- [no_tags]

  sqlalchemy.logging has been renamed to sqlalchemy.log.

- [no_tags]

  The transitional sqlalchemy.log.SADeprecationWarning alias for the warning’s definition in sqlalchemy.exc has been removed.

- [no_tags]

  exc.AssertionError has been removed and usage replaced with Python’s built-in AssertionError.

- [no_tags]

  The behavior of MapperExtensions attached to multiple, entity_name= primary mappers for a single class has been altered. The first mapper() defined for a class is the only mapper eligible for the MapperExtension ‘instrument_class’, ‘init_instance’ and ‘init_failed’ events. This is backwards incompatible; previously the extensions of last mapper defined would receive these events.

- [firebird]

  Added support for returning values from inserts (2.0+ only), updates and deletes (2.1+ only).

- [postgres]

  Added Index reflection support to Postgres, using a great patch we long neglected, submitted by Ken Kuhlman.

  References: #714