Pin sqlalchemy to latest version 1.4.20

[pyup-bot]

This PR pins SQLAlchemy to the latest release 1.4.20.

Changelog

1.4.20

:released: June 28, 2021

 .. change::
     :tags: bug, regression, orm
     :tickets: 6680

     Fixed regression in ORM regarding an internal reconstitution step for the
     :func:`_orm.with_polymorphic` construct, when the user-facing object is
     garbage collected as the query is processed. The reconstitution was not
     ensuring the sub-entities for the "polymorphic" case were handled, leading
     to an ``AttributeError``.

 .. change::
     :tags: usecase, sql
     :tickets: 6646

     Add a impl parameter to :class:`_types.PickleType` constructor, allowing
     any arbitary type to be used in place of the default implementation of
     :class:`_types.LargeBinary`. Pull request courtesy jason3gb.

 .. change::
     :tags: bug, engine
     :tickets: 5348

     Fixed an issue in the C extension for the :class:`_result.Row` class which
     could lead to a memory leak in the unlikely case of a :class:`_result.Row`
     object which referred to an ORM object that then was mutated to refer back
     to the ``Row`` itself, creating a cycle. The Python C APIs for tracking GC
     cycles has been added to the native :class:`_result.Row` implementation to
     accommodate for this case.


 .. change::
     :tags: bug, engine
     :tickets: 6665

     Fixed old issue where a :func:`_sql.select()` made against the token "*",
     which then yielded exactly one column, would fail to correctly organize the
     ``cursor.description`` column name into the keys of the result object.



 .. change::
     :tags: usecase, mysql
     :tickets: 6659

     Made a small adjustment in the table reflection feature of the MySQL
     dialect to accommodate for alternate MySQL-oriented databases such as TiDB
     which include their own "comment" directives at the end of a constraint
     directive within "CREATE TABLE" where the format doesn't have the
     additional space character after the comment, in this case the TiDB
     "clustered index" feature. Pull request courtesy Daniël van Eeden.

 .. change::
     :tags: bug, schema
     :tickets: 6685

     Fixed issue where passing ``None`` for the value of
     :paramref:`_schema.Table.prefixes` would not store an empty list, but
     rather the constant ``None``, which may be unexpected by third party
     dialects. The issue is revealed by a usage in recent versions of Alembic
     that are passing ``None`` for this value. Pull request courtesy Kai
     Mueller.

 .. change::
     :tags: bug, regression, ext
     :tickets: 6679

     Fixed regression in :mod:`sqlalchemy.ext.automap` extension such that the
     use case of creating an explicit mapped class to a table that is also the
     :paramref:`_orm.relationship.secondary` element of a
     :func:`_orm.relationship` that automap will be generating would emit the
     "overlaps" warnings introduced in 1.4 and discussed at :ref:`error_qzyx`.
     While generating this case from automap is still subject to the same
     caveats that the "overlaps" warning refers towards, as automap is intended
     for more ad-hoc use cases, the condition which produces the warning is
     disabled when a many-to-many relationship with this particular pattern is
     generated.



 .. change::
     :tags: bug, regression, orm
     :tickets: 6678

     Adjusted :meth:`_orm.Query.union` and similar set operations to be
     correctly compatible with the new capabilities just added in
     :ticket:`6661`, with SQLAlchemy 1.4.19, such that the SELECT statements
     rendered as elements of the UNION or other set operation will include
     directly mapped columns that are mapped as deferred; this both fixes a
     regression involving unions with multiple levels of nesting that would
     produce a column mismatch, and also allows the :func:`_orm.undefer` option
     to be used at the top level of such a :class:`_orm.Query` without having to
     apply the option to each of the elements within the UNION.

 .. change::
     :tags: bug, sql, orm
     :tickets: 6668

     Fixed the class hierarchy for the :class:`_schema.Sequence` and the more
     general :class:`_schema.DefaultGenerator` base, as these are "executable"
     as statements they need to include :class:`_sql.Executable` in their
     hierarchy, not just :class:`_roles.StatementRole` as was applied
     arbitrarily to :class:`_schema.Sequence` previously. The fix allows
     :class:`_schema.Sequence` to work in all ``.execute()`` methods including
     with :meth:`_orm.Session.execute` which was not working in the case that a
     :meth:`_orm.SessionEvents.do_orm_execute` handler was also established.


 .. change::
     :tags: bug, orm
     :tickets: 6538

     Adjusted the check in the mapper for a callable object that is used as a
     ``validates`` validator function or a ``reconstructor`` reconstruction
     function, to check for "callable" more liberally such as to accommodate
     objects based on fundamental attributes like ``__func__`` and
     ``__call___``, rather than testing for ``MethodType`` / ``FunctionType``,
     allowing things like cython functions to work properly. Pull request
     courtesy Miłosz Stypiński.

.. changelog::

1.4.19

:released: June 22, 2021

 .. change::
     :tags: bug, mssql
     :tickets: 6658

     Fixed bug where the "schema_translate_map" feature would fail to function
     correctly in conjunction with an INSERT into a table that has an IDENTITY
     column, where the value of the IDENTITY column were specified in the values
     of the INSERT thus triggering SQLAlchemy's feature of setting IDENTITY
     INSERT to "on"; it's in this directive where the schema translate map would
     fail to be honored.


 .. change::
     :tags: bug, sql
     :tickets: 6663

     Fixed issue in CTE constructs mostly relevant to ORM use cases where a
     recursive CTE against "anonymous" labels such as those seen in ORM
     ``column_property()`` mappings would render in the
     ``WITH RECURSIVE xyz(...)`` section as their raw internal label and not a
     cleanly anonymized name.

 .. change::
     :tags: mssql, change
     :tickets: 6503, 6253

     Made improvements to the server version regexp used by the pymssql dialect
     to prevent a regexp overflow in case of an invalid version string.

 .. change::
     :tags: bug, orm, regression
     :tickets: 6503, 6253

     Fixed further regressions in the same area as that of :ticket:`6052` where
     loader options as well as invocations of methods like
     :meth:`_orm.Query.join` would fail if the left side of the statement for
     which the option/join depends upon were replaced by using the
     :meth:`_orm.Query.with_entities` method, or when using 2.0 style queries
     when using the :meth:`_sql.Select.with_only_columns` method. A new set of
     state has been added to the objects which tracks the "left" entities that
     the options / join were made against which is memoized when the lead
     entities are changed.

 .. change::
     :tags: bug, asyncio, postgresql
     :tickets: 6652

     Fixed bug in asyncio implementation where the greenlet adaptation system
     failed to propagate ``BaseException`` subclasses, most notably including
     ``asyncio.CancelledError``, to the exception handling logic used by the
     engine to invalidate and clean up the connection, thus preventing
     connections from being correctly disposed when a task was cancelled.



 .. change::
     :tags: usecase, asyncio
     :tickets: 6583

     Implemented :class:`_asyncio.async_scoped_session` to address some
     asyncio-related incompatibilities between :class:`_orm.scoped_session` and
     :class:`_asyncio.AsyncSession`, in which some methods (notably the
     :meth:`_asyncio.async_scoped_session.remove` method) should be used with
     the ``await`` keyword.

     .. seealso::

         :ref:`asyncio_scoped_session`

 .. change::
     :tags: usecase, mysql
     :tickets: 6132

     Added new construct :class:`_mysql.match`, which provides for the full
     range of MySQL's MATCH operator including multiple column support and
     modifiers. Pull request courtesy Anton Kovalevich.

     .. seealso::

         :class:`_mysql.match`

 .. change::
     :tags: bug, postgresql, oracle
     :tickets: 6649

     Fixed issue where the ``INTERVAL`` datatype on PostgreSQL and Oracle would
     produce an ``AttributeError`` when used in the context of a comparison
     operation against a ``timedelta()`` object. Pull request courtesy
     MajorDallas.

 .. change::
     :tags: bug, mypy
     :tickets: 6476

     Fixed issue in mypy plugin where class info for a custom declarative base
     would not be handled correctly on a cached mypy pass, leading to an
     AssertionError being raised.

 .. change::
     :tags: bug, orm
     :tickets: 6661

     Refined the behavior of ORM subquery rendering with regards to deferred
     columns and column properties to be more compatible with that of 1.3 while
     also providing for 1.4's newer features. As a subquery in 1.4 does not make
     use of loader options, including :func:`_orm.undefer`, a subquery that is
     against an ORM entity with deferred attributes will now render those
     deferred attributes that refer directly to mapped table columns, as these
     are needed in the outer SELECT if that outer SELECT makes use of these
     columns; however a deferred attribute that refers to a composed SQL
     expression as we normally do with :func:`_orm.column_property` will not be
     part of the subquery, as these can be selected explicitly if needed in the
     subquery. If the entity is being SELECTed from this subquery, the column
     expression can still render on "the outside" in terms of the derived
     subquery columns. This produces essentially the same behavior as when
     working with 1.3. However in this case the fix has to also make sure that
     the ``.selected_columns`` collection of an ORM-enabled :func:`_sql.select`
     also follows these rules, which in particular allows recursive CTEs to
     render correctly in this scenario, which were previously failing to render
     correctly due to this issue.

 .. change::
     :tags: bug, postgresql
     :tickets: 6621

     Fixed issue where the pool "pre ping" feature would implicitly start a
     transaction, which would then interfere with custom transactional flags
     such as PostgreSQL's "read only" mode when used with the psycopg2 driver.


.. changelog::

1.4.18

:released: June 10, 2021

 .. change::
     :tags: bug, orm
     :tickets: 6072, 6487

     Clarified the current purpose of the
     :paramref:`_orm.relationship.bake_queries` flag, which in 1.4 is to enable
     or disable "lambda caching" of statements within the "lazyload" and
     "selectinload" loader strategies; this is separate from the more
     foundational SQL query cache that is used for most statements.
     Additionally, the lazy loader no longer uses its own cache for many-to-one
     SQL queries, which was an implementation quirk that doesn't exist for any
     other loader scenario. Finally, the "lru cache" warning that the lazyloader
     and selectinloader strategies could emit when handling a wide array of
     class/relationship combinations has been removed; based on analysis of some
     end-user cases, this warning doesn't suggest any significant issue. While
     setting ``bake_queries=False`` for such a relationship will remove this
     cache from being used, there's no particular performance gain in this case
     as using no caching vs. using a cache that needs to refresh often likely
     still wins out on the caching being used side.


 .. change::
     :tags: bug, asyncio
     :tickets: 6575

     Fixed an issue that presented itself when using the :class:`_pool.NullPool`
     or the :class:`_pool.StaticPool` with an async engine. This mostly affected
     the aiosqlite dialect.

 .. change::
     :tags: bug, sqlite, regression
     :tickets: 6586

     The fix for pysqlcipher released in version 1.4.3 :ticket:`5848` was
     unfortunately non-working, in that the new ``on_connect_url`` hook was
     erroneously not receiving a ``URL`` object under normal usage of
     :func:`_sa.create_engine` and instead received a string that was unhandled;
     the test suite failed to fully set up the actual conditions under which
     this hook is called. This has been fixed.

 .. change::
     :tags: bug, postgresql, regression
     :tickets: 6581

     Fixed regression where using the PostgreSQL "INSERT..ON CONFLICT" structure
     would fail to work with the psycopg2 driver if it were used in an
     "executemany" context along with bound parameters in the "SET" clause, due
     to the implicit use of the psycopg2 fast execution helpers which are not
     appropriate for this style of INSERT statement; as these helpers are the
     default in 1.4 this is effectively a regression.  Additional checks to
     exclude this kind of statement from that particular extension have been
     added.

 .. change::
     :tags: bug, orm, regression
     :tickets: 6285

     Adjusted the means by which classes such as :class:`_orm.scoped_session`
     and :class:`_asyncio.AsyncSession` are generated from the base
     :class:`_orm.Session` class, such that custom :class:`_orm.Session`
     subclasses such as that used by Flask-SQLAlchemy don't need to implement
     positional arguments when they call into the superclass method, and can
     continue using the same argument styles as in previous releases.

 .. change::
     :tags: bug, orm, regression
     :tickets: 6595

     Fixed issue where query production for joinedload against a complex left
     hand side involving joined-table inheritance could fail to produce a
     correct query, due to a clause adaption issue.

 .. change::
     :tags: bug, orm, regression, performance
     :tickets: 6596

     Fixed regression involving how the ORM would resolve a given mapped column
     to a result row, where under cases such as joined eager loading, a slightly
     more expensive "fallback" could take place to set up this resolution due to
     some logic that was removed since 1.3. The issue could also cause
     deprecation warnings involving column resolution to be emitted when using a
     1.4 style query with joined eager loading.

 .. change::
     :tags: bug, orm
     :tickets: 6591

     Fixed issue in experimental "select ORM objects from INSERT/UPDATE" use
     case where an error was raised if the statement were against a
     single-table-inheritance subclass.

 .. change::
     :tags: bug, asyncio
     :tickets: 6592

     Added ``asyncio.exceptions.TimeoutError``,
     ``asyncio.exceptions.CancelledError`` as so-called "exit exceptions", a
     class of exceptions that include things like ``GreenletExit`` and
     ``KeyboardInterrupt``, which are considered to be events that warrant
     considering a DBAPI connection to be in an unusable state where it should
     be recycled.

 .. change::
     :tags: bug, orm
     :tickets: 6400

     The warning that's emitted for :func:`_orm.relationship` when multiple
     relationships would overlap with each other as far as foreign key
     attributes written towards, now includes the specific "overlaps" argument
     to use for each warning in order to silence the warning without changing
     the mapping.

 .. change::
     :tags: usecase, asyncio
     :tickets: 6319

     Implemented a new registry architecture that allows the ``Async`` version
     of an object, like ``AsyncSession``, ``AsyncConnection``, etc., to be
     locatable given the proxied "sync" object, i.e. ``Session``,
     ``Connection``. Previously, to the degree such lookup functions were used,
     an ``Async`` object would be re-created each time, which was less than
     ideal as the identity and state of the "async" object would not be
     preserved across calls.

     From there, new helper functions :func:`_asyncio.async_object_session`,
     :func:`_asyncio.async_session` as well as a new :class:`_orm.InstanceState`
     attribute :attr:`_orm.InstanceState.async_session` have been added, which
     are used to retrieve the original :class:`_asyncio.AsyncSession` associated
     with an ORM mapped object, a :class:`_orm.Session` associated with an
     :class:`_asyncio.AsyncSession`, and an :class:`_asyncio.AsyncSession`
     associated with an :class:`_orm.InstanceState`, respectively.

     This patch also implements new methods
     :meth:`_asyncio.AsyncSession.in_nested_transaction`,
     :meth:`_asyncio.AsyncSession.get_transaction`,
     :meth:`_asyncio.AsyncSession.get_nested_transaction`.

.. changelog::

1.4.17

:released: May 29, 2021

 .. change::
     :tags: bug, orm, regression
     :tickets: 6558

     Fixed regression caused by just-released performance fix mentioned in 6550
     where a query.join() to a relationship could produce an AttributeError if
     the query were made against non-ORM structures only, a fairly unusual
     calling pattern.

.. changelog::

1.4.16

:released: May 28, 2021

 .. change::
     :tags: bug, engine
     :tickets: 6482

     Fixed issue where an ` sign in the database portion of a URL would not
     be interpreted correctly if the URL also had a username:password section.


 .. change::
     :tags: bug, ext
     :tickets: 6529

     Fixed a deprecation warning that was emitted when using
     :func:`_automap.automap_base` without passing an existing
     ``Base``.


 .. change::
     :tags: bug, pep484
     :tickets: 6461

     Remove pep484 types from the code.
     Current effort is around the stub package, and having typing in
     two places makes thing worse, since the types in the SQLAlchemy
     source were usually outdated compared to the version in the stubs.

 .. change::
     :tags: usecase, mssql
     :tickets: 6464

     Implemented support for a :class:`_sql.CTE` construct to be used directly
     as the target of a :func:`_sql.delete` construct, i.e. "WITH ... AS cte
     DELETE FROM cte". This appears to be a useful feature of SQL Server.

 .. change::
     :tags: bug, general
     :tickets: 6540, 6543

     Resolved various deprecation warnings which were appearing as of Python
     version 3.10.0b1.

 .. change::
     :tags: bug, orm
     :tickets: 6471

     Fixed issue when using :paramref:`_orm.relationship.cascade_backrefs`
     parameter set to ``False``, which per :ref:`change_5150` is set to become
     the standard behavior in SQLAlchemy 2.0, where adding the item to a
     collection that uniquifies, such as ``set`` or ``dict`` would fail to fire
     a cascade event if the object were already associated in that collection
     via the backref. This fix represents a fundamental change in the collection
     mechanics by introducing a new event state which can fire off for a
     collection mutation even if there is no net change on the collection; the
     action is now suited using a new event hook
     :meth:`_orm.AttributeEvents.append_wo_mutation`.



 .. change::
     :tags: bug, orm, regression
     :tickets: 6550

     Fixed regression involving clause adaption of labeled ORM compound
     elements, such as single-table inheritance discriminator expressions with
     conditionals or CASE expressions, which could cause aliased expressions
     such as those used in ORM join / joinedload operations to not be adapted
     correctly, such as referring to the wrong table in the ON clause in a join.

     This change also improves a performance bump that was located within the
     process of invoking :meth:`_sql.Select.join` given an ORM attribute
     as a target.

 .. change::
     :tags: bug, orm, regression
     :tickets: 6495

     Fixed regression where the full combination of joined inheritance, global
     with_polymorphic, self-referential relationship and joined loading would
     fail to be able to produce a query with the scope of lazy loads and object
     refresh operations that also attempted to render the joined loader.

 .. change::
     :tags: bug, engine
     :tickets: 6329

     Fixed a long-standing issue with :class:`.URL` where query parameters
     following the question mark would not be parsed correctly if the URL did
     not contain a database portion with a backslash.

 .. change::
     :tags: bug, sql, regression
     :tickets: 6549

     Fixed regression in dynamic loader strategy and :func:`_orm.relationship`
     overall where the :paramref:`_orm.relationship.order_by` parameter were
     stored as a mutable list, which could then be mutated when combined with
     additional "order_by" methods used against the dynamic query object,
     causing the ORDER BY criteria to continue to grow repetitively.

 .. change::
     :tags: bug, orm
     :tickets: 6484

     Enhanced the bind resolution rules for :meth:`_orm.Session.execute` so that
     when a non-ORM statement such as an :func:`_sql.insert` construct
     nonetheless is built against ORM objects, to the greatest degree possible
     the ORM entity will be used to resolve the bind, such as for a
     :class:`_orm.Session` that has a bind map set up on a common superclass
     without specific mappers or tables named in the map.

 .. change::
     :tags: bug, regression, ext
     :tickets: 6390

     Fixed regression in the ``sqlalchemy.ext.instrumentation`` extension that
     prevented instrumentation disposal from working completely. This fix
     includes both a 1.4 regression fix as well as a fix for a related issue
     that existed in 1.3 also.   As part of this change, the
     :class:`sqlalchemy.ext.instrumentation.InstrumentationManager` class now
     has a new method ``unregister()``, which replaces the previous method
     ``dispose()``, which was not called as of version 1.4.


.. changelog::

1.4.15

:released: May 11, 2021

 .. change::
     :tags: bug, documentation, mysql
     :tickets: 5397

     Added support for the ``ssl_check_hostname=`` parameter in mysql connection
     URIs and updated the mysql dialect documentation regarding secure
     connections. Original pull request courtesy of Jerry Zhao.

 .. change::
     :tags: bug, orm, regression
     :tickets: 6449

     Fixed additional regression caused by "eager loaders run on unexpire"
     feature :ticket:`1763` where the feature would run for a
     ``contains_eager()`` eagerload option in the case that the
     ``contains_eager()`` were chained to an additional eager loader option,
     which would then produce an incorrect query as the original query-bound
     join criteria were no longer present.

 .. change::
     :tags: feature, general
     :tickets: 6241

     A new approach has been applied to the warnings system in SQLAlchemy to
     accurately predict the appropriate stack level for each warning
     dynamically. This allows evaluating the source of SQLAlchemy-generated
     warnings and deprecation warnings to be more straightforward as the warning
     will indicate the source line within end-user code, rather than from an
     arbitrary level within SQLAlchemy's own source code.

 .. change::
     :tags: bug, orm
     :tickets: 6459

     Fixed issue in subquery loader strategy which prevented caching from
     working correctly. This would have been seen in the logs as a "generated"
     message instead of "cached" for all subqueryload SQL emitted, which by
     saturating the cache with new keys would degrade overall performance; it
     also would produce "LRU size alert" warnings.


 .. change::
     :tags: bug, sql
     :tickets: 6460

     Adjusted the logic added as part of :ticket:`6397` in 1.4.12 so that
     internal mutation of the :class:`.BindParameter` object occurs within the
     clause construction phase as it did before, rather than in the compilation
     phase. In the latter case, the mutation still produced side effects against
     the incoming construct and additionally could potentially interfere with
     other internal mutation routines.

.. changelog::

1.4.14

:released: May 6, 2021

 .. change::
     :tags: bug, regression, orm
     :tickets: 6426

     Fixed regression involving ``lazy='dynamic'`` loader in conjunction with a
     detached object. The previous behavior was that the dynamic loader upon
     calling methods like ``.all()`` returns empty lists for detached objects
     without error, this has been restored; however a warning is now emitted as
     this is not the correct result. Other dynamic loader scenarios correctly
     raise ``DetachedInstanceError``.

 .. change::
     :tags: bug, regression, sql
     :tickets: 6428

     Fixed regression caused by the "empty in" change just made in
     :ticket:`6397` 1.4.12 where the expression needs to be parenthesized for
     the "not in" use case, otherwise the condition will interfere with the
     other filtering criteria.


 .. change::
     :tags: bug, sql, regression
     :tickets: 6436

     The :class:`.TypeDecorator` class will now emit a warning when used in SQL
     compilation with caching unless the ``.cache_ok`` flag is set to ``True``
     or ``False``. A new class-level attribute :attr:`.TypeDecorator.cache_ok`
     may be set which will be used as an indication that all the parameters
     passed to the object are safe to be used as a cache key if set to ``True``,
     ``False`` means they are not.

 .. change::
     :tags: engine, bug, regression
     :tickets: 6427

     Established a deprecation path for calling upon the
     :meth:`_cursor.CursorResult.keys` method for a statement that returns no
     rows to provide support for legacy patterns used by the "records" package
     as well as any other non-migrated applications. Previously, this would
     raise :class:`.ResourceClosedException` unconditionally in the same way as
     it does when attempting to fetch rows. While this is the correct behavior
     going forward, the :class:`_cursor.LegacyCursorResult` object will now in
     this case return an empty list for ``.keys()`` as it did in 1.3, while also
     emitting a 2.0 deprecation warning. The :class:`_cursor.CursorResult`, used
     when using a 2.0-style "future" engine, will continue to raise as it does
     now.

 .. change::
     :tags: usecase, engine, orm
     :tickets: 6288

     Applied consistent behavior to the use case of
     calling ``.commit()`` or ``.rollback()`` inside of an existing
     ``.begin()`` context manager, with the addition of potentially
     emitting SQL within the block subsequent to the commit or rollback.
     This change continues upon the change first added in
     :ticket:`6155` where the use case of calling "rollback" inside of
     a ``.begin()`` contextmanager block was proposed:

     * calling ``.commit()`` or ``.rollback()`` will now be allowed
       without error or warning within all scopes, including
       that of legacy and future :class:`_engine.Engine`, ORM
       :class:`_orm.Session`, asyncio :class:`.AsyncEngine`.  Previously,
       the :class:`_orm.Session` disallowed this.

     * The remaining scope of the context manager is then closed;
       when the block ends, a check is emitted to see if the transaction
       was already ended, and if so the block returns without action.

     * It will now raise **an error** if subsequent SQL of any kind
       is emitted within the block, **after** ``.commit()`` or
       ``.rollback()`` is called.   The block should be closed as
       the state of the executable object would otherwise be undefined
       in this state.

.. changelog::

1.4.13

:released: May 3, 2021

 .. change::
     :tags: bug, regression, orm
     :tickets: 6410

     Fixed regression in ``selectinload`` loader strategy that would cause it to
     cache its internal state incorrectly when handling relationships that join
     across more than one column, such as when using a composite foreign key.
     The invalid caching would then cause other unrelated loader operations to
     fail.


 .. change::
     :tags: bug, orm, regression
     :tickets: 6414

     Fixed regression where :meth:`_orm.Query.filter_by` would not work if the
     lead entity were a SQL function or other expression derived from the
     primary entity in question, rather than a simple entity or column of that
     entity. Additionally, improved the behavior of
     :meth:`_sql.Select.filter_by` overall to work with column expressions even
     in a non-ORM context.

 .. change::
     :tags: bug, engine, regression
     :tickets: 6408

     Restored a legacy transactional behavior that was inadvertently removed
     from the :class:`_engine.Connection` as it was never tested as a known use
     case in previous versions, where calling upon the
     :meth:`_engine.Connection.begin_nested` method, when no transaction is
     present, does not create a SAVEPOINT at all and instead starts an outer
     transaction, returning a :class:`.RootTransaction` object instead of a
     :class:`.NestedTransaction` object.  This :class:`.RootTransaction` then
     will emit a real COMMIT on the database connection when committed.
     Previously, the 2.0 style behavior was present in all cases that would
     autobegin a transaction but not commit it, which is a behavioral change.

     When using a :term:`2.0 style` connection object, the behavior is unchanged
     from previous 1.4 versions; calling :meth:`_future.Connection.begin_nested`
     will "autobegin" the outer transaction if not already present, and then as
     instructed emit a SAVEPOINT, returning the :class:`.NestedTransaction`
     object. The outer transaction is committed by calling upon
     :meth:`_future.Connection.commit`, as is "commit-as-you-go" style usage.

     In non-"future" mode, while the old behavior is restored, it also
     emits a 2.0 deprecation warning as this is a legacy behavior.


 .. change::
     :tags: bug, asyncio, regression
     :tickets: 6409

     Fixed a regression introduced by :ticket:`6337` that would create an
     ``asyncio.Lock`` which could be attached to the wrong loop when
     instantiating the async engine before any asyncio loop was started, leading
     to an asyncio error message when attempting to use the engine under certain
     circumstances.

 .. change::
     :tags: bug, orm, regression
     :tickets: 6419

     Fixed regression where using :func:`_orm.selectinload` and
     :func:`_orm.subqueryload` to load a two-level-deep path would lead to an
     attribute error.

 .. change::
     :tags: bug, orm, regression
     :tickets: 6420

     Fixed regression where using the :func:`_orm.noload` loader strategy in
     conjunction with a "dynamic" relationship would lead to an attribute error
     as the noload strategy would attempt to apply itself to the dynamic loader.

 .. change::
     :tags: usecase, postgresql
     :tickets: 6198

     Add support for server side cursors in the pg8000 dialect for PostgreSQL.
     This allows use of the
     :paramref:`.Connection.execution_options.stream_results` option.

.. changelog::

1.4.12

:released: April 29, 2021

 .. change::
     :tags: bug, orm, regression, caching
     :tickets: 6391

     Fixed critical regression where bound parameter tracking as used in the SQL
     caching system could fail to track all parameters for the case where the
     same SQL expression containing a parameter were used in an ORM-related
     query using a feature such as class inheritance, which was then embedded in
     an enclosing expression which would make use of that same expression
     multiple times, such as a UNION. The ORM would individually copy the
     individual SELECT statements as part of compilation with class inheritance,
     which then embedded in the enclosing statement would fail to accommodate
     for all parameters. The logic that tracks this condition has been adjusted
     to work for multiple copies of a parameter.

 .. change::
     :tags: bug, sql
     :tickets: 6258, 6397

     Revised the "EMPTY IN" expression to no longer rely upon using a subquery,
     as this was causing some compatibility and performance problems. The new
     approach for selected databases takes advantage of using a NULL-returning
     IN expression combined with the usual "1 != 1" or "1 = 1" expression
     appended by AND or OR. The expression is now the default for all backends
     other than SQLite, which still had some compatibility issues regarding
     tuple "IN" for older SQLite versions.

     Third party dialects can still override how the "empty set" expression
     renders by implementing a new compiler method
     ``def visit_empty_set_op_expr(self, type_, expand_op)``, which takes
     precedence over the existing
     ``def visit_empty_set_expr(self, element_types)`` which remains in place.


 .. change::
     :tags: bug, orm
     :tickets: 6350

     Fixed two distinct issues mostly affecting
     :class:`_hybrid.hybrid_property`, which would come into play under common
     mis-configuration scenarios that were silently ignored in 1.3, and now
     failed in 1.4, where the "expression" implementation would return a non
     :class:`_sql.ClauseElement` such as a boolean value. For both issues, 1.3's
     behavior was to silently ignore the mis-configuration and ultimately
     attempt to interpret the value as a SQL expression, which would lead to an
     incorrect query.

     * Fixed issue regarding interaction of the attribute system with
       hybrid_property, where if the ``__clause_element__()`` method of the
       attribute returned a non-:class:`_sql.ClauseElement` object, an internal
       ``AttributeError`` would lead the attribute to return the ``expression``
       function on the hybrid_property itself, as the attribute error was
       against the name ``.expression`` which would invoke the ``__getattr__()``
       method as a fallback. This now raises explicitly. In 1.3 the
       non-:class:`_sql.ClauseElement` was returned directly.

     * Fixed issue in SQL argument coercions system where passing the wrong
       kind of object to methods that expect column expressions would fail if
       the object were altogether not a SQLAlchemy object, such as a Python
       function, in cases where the object were not just coerced into a bound
       value. Again 1.3 did not have a comprehensive argument coercion system
       so this case would also pass silently.


 .. change::
     :tags: bug, orm
     :tickets: 6378

     Fixed issue where using a :class:`_sql.Select` as a subquery in an ORM
     context would modify the :class:`_sql.Select` in place to disable
     eagerloads on that object, which would then cause that same
     :class:`_sql.Select` to not eagerload if it were then re-used in a
     top-level execution context.


 .. change::
     :tags: bug, regression, sql
     :tickets: 6343

     Fixed regression where usage of the :func:`_sql.text` construct inside the
     columns clause of a :class:`_sql.Select` construct, which is better handled
     by using a :func:`_sql.literal_column` construct, would nonetheless prevent
     constructs like :func:`_sql.union` from working correctly. Other use cases,
     such as constructing subuqeries, continue to work the same as in prior
     versions where the :func:`_sql.text` construct is silently omitted from the
     collection of exported columns.   Also repairs similar use within the
     ORM.


 .. change::
     :tags: bug, regression, sql
     :tickets: 6261

     Fixed regression involving legacy methods such as
     :meth:`_sql.Select.append_column` where internal assertions would fail.

 .. change::
     :tags: usecase, sqlite
     :tickets: 6379

     Default to using ``SingletonThreadPool`` for in-memory SQLite databases
     created using URI filenames. Previously the default pool used was the
     ``NullPool`` that precented sharing the same database between multiple
     engines.

 .. change::
     :tags: bug, regression, sql
     :tickets: 6300

     Fixed regression caused by :ticket:`5395` where tuning back the check for
     sequences in :func:`_sql.select` now caused failures when doing 2.0-style
     querying with a mapped class that also happens to have an ``__iter__()``
     method. Tuned the check some more to accommodate this as well as some other
     interesting ``__iter__()`` scenarios.


 .. change::
     :tags: bug, mssql, schema
     :tickets: 6345

     Add :meth:`_types.TypeEngine.as_generic` support for
     :class:`sqlalchemy.dialects.mysql.BIT` columns, mapping
     them to :class:`_sql.sqltypes.Boolean`.

 .. change::
     :tags: bug, orm, regression
     :tickets: 6360, 6359

     Fixed issue where the new :ref:`autobegin <session_autobegin>` behavior
     failed to "autobegin" in the case where an existing persistent object has
     an attribute change, which would then impact the behavior of
     :meth:`_orm.Session.rollback` in that no snapshot was created to be rolled
     back. The "attribute modify" mechanics have been updated to ensure
     "autobegin", which does not perform any database work, does occur when
     persistent attributes change in the same manner as when
     :meth:`_orm.Session.add` is called. This is a regression as in 1.3, the
     rollback() method always had a transaction to roll back and would expire
     every time.

 .. change::
     :tags: bug, mssql, regression
     :tickets: 6366

     Fixed regression caused by :ticket:`6306` which added support for
     ``DateTime(timezone=True)``, where the previous behavior of the pyodbc
     driver of implicitly dropping the tzinfo from a timezone-aware date when
     INSERTing into a timezone-naive DATETIME column were lost, leading to a SQL
     Server error when inserting timezone-aware datetime objects into
     timezone-native database columns.

 .. change::
     :tags: orm, bug, regression
     :tickets: 6386

     Fixed regression in ORM where using hybrid property to indicate an
     expression from a different entity would confuse the column-labeling logic
     in the ORM and attempt to derive the name of the hybrid from that other
     class, leading to an attribute error. The owning class of the hybrid
     attribute is now tracked along with the name.

 .. change::
     :tags: orm, bug, regression
     :tickets: 6401

     Fixed regression in hybrid_property where a hybrid against a SQL function
     would generate an ``AttributeError`` when attempting to generate an entry
     for the ``.c`` collection of a subquery in some cases; among other things
     this would impact its use in cases like that of ``Query.count()``.


 .. change::
     :tags: bug, postgresql
     :tickets: 6373

     Fixed very old issue where the :class:`_types.Enum` datatype would not
     inherit the :paramref:`_schema.MetaData.schema` parameter of a
     :class:`_schema.MetaData` object when that object were passed to the
     :class:`_types.Enum` using :paramref:`_types.Enum.metadata`.

 .. change::
     :tags: bug, orm, dataclasses
     :tickets: 6346

     Adjusted the declarative scan for dataclasses so that the inheritance
     behavior of :func:`_orm.declared_attr` established on a mixin, when using
     the new form of having it inside of a ``dataclasses.field()`` construct and
     not actually a descriptor attribute on the class, correctly accommodates
     the case when the target class to be mapped is a subclass of an existing
     mapped class which has already mapped that :func:`_orm.declared_attr`, and
     therefore should not be re-applied to this class.


 .. change::
     :tags: bug, schema, mysql, mariadb, oracle, postgresql
     :tickets: 6338

     Ensure that the MySQL and MariaDB dialect ignore the
     :class:`_sql.Identity` construct while rendering the ``AUTO_INCREMENT``
     keyword in a create table.

     The Oracle and PostgreSQL compiler was updated to not render
     :class:`_sql.Identity` if the database version does not support it
     (Oracle < 12 and PostgreSQL < 10). Previously it was rendered regardless
     of the database version.

 .. change::
     :tags: bug, orm
     :tickets: 6353

     Fixed an issue with the (deprecated in 1.4)
     :meth:`_schema.ForeignKeyConstraint.copy` method that caused an error when
     invoked with the ``schema`` argument.

 .. change::
     :tags: bug, engine
     :tickets: 6361

     Fixed issue where usage of an explicit :class:`.Sequence` would produce
     inconsistent "inline" behavior for an :class:`.Insert` construct that
     includes multiple values phrases; the first seq would be inline but
     subsequent ones would be "pre-execute", leading to inconsistent sequence
     ordering. The sequence expressions are now fully inline.

.. changelog::

1.4.11

:released: April 21, 2021

 .. change::
     :tags: bug, engine, regression
     :tickets: 6337

     Fixed critical regression caused by the change in :ticket:`5497` where the
     connection pool "init" phase no longer occurred within mutexed isolation,
     allowing other threads to proceed with the dialect uninitialized, which
     could then impact the compilation of SQL statements.


 .. change::
     :tags: bug, orm, regression, declarative
     :tickets: 6331

     Fixed regression where recent changes to support Python dataclasses had the
     inadvertent effect that an ORM mapped class could not successfully override
     the ``__new__()`` method.

.. changelog::

1.4.10

:released: April 20, 2021

 .. change::
     :tags: bug, declarative, regression
     :tickets: 6291

     Fixed :func:`_declarative.instrument_declarative` that called
     a non existing registry method.

 .. change::
     :tags: bug, orm
     :tickets: 6320

     Fixed bug in new :func:`_orm.with_loader_criteria` feature where using a
     mixin class with :func:`_orm.declared_attr` on an attribute that were
     accessed inside the custom lambda would emit a warning regarding using an
     unmapped declared attr, when the lambda callable were first initialized.
     This warning is now prevented using special instrumentation for this
     lambda initialization step.


 .. change::
     :tags: usecase, mssql
     :tickets: 6306

     The :paramref:`_types.DateTime.timezone` parameter when set to ``True``
     will now make use of the ``DATETIMEOFFSET`` column type with SQL Server
     when used to emit DDL, rather than ``DATETIME`` where the flag was silently
     ignored.

 .. change::
     :tags: orm, bug, regression
     :tickets: 6326

     Fixed additional regression caused by the "eagerloaders on refresh" feature
     added in :ticket:`1763` where the refresh operation historically would set
     ``populate_existing``, which given the new feature now overwrites pending
     changes on eagerly loaded objects when autoflush is false. The
     populate_existing flag has been turned off for this case and a more
     specific method used to ensure the correct attributes refreshed.

 .. change::
     :tags: bug, orm, result
     :tickets: 6299

     Fixed an issue when using 2.0 style execution that prevented using
     :meth:`_result.Result.scalar_one` or
     :meth:`_result.Result.scalar_one_or_none` after calling
     :meth:`_result.Result.unique`, for the case where the ORM is returning a
     single-element row in any case.

 .. change::
     :tags: bug, sql
     :tickets: 6327

     Fixed issue in SQL compiler where the bound parameters set up for a
     :class:`.Values` construct wouldn't be positionally tracked correctly if
     inside of a :class:`_sql.CTE`, affecting database drivers that support
     VALUES + ctes and use positional parameters such as SQL Server in
     particular as well as asyncpg.   The fix also repairs support for
     compiler flags such as ``literal_binds``.

 .. change::
     :tags: bug, schema
     :tickets: 6287

     Fixed issue where :func:`_functions.next_value` was not deriving its type
     from the corresponding :class:`_schema.Sequence`, instead hardcoded to
     :class:`_types.Integer`. The specific numeric type is now used.

 .. change::
     :tags: bug, mypy
     :tickets: 6255

     Fixed issue where mypy plugin would not correctly interpret an explicit
     :class:`_orm.Mapped` annotation in conjunction with a
     :func:`_orm.relationship` that refers to a class by string name; the
     correct annotation would be downgraded to a less specific one leading to
     typing errors.

 .. change::
     :tags: bug, sql
     :tickets: 6256

     Repaired and solidified issues regarding custom functions and other
     arbitrary expression constructs which within SQLAlchemy's column labeling
     mechanics would seek to use ``str(obj)`` to get a string representation to
     use as an anonymous column name in the ``.c`` collection of a subquery.
     This is a very legacy behavior that performs poorly and leads to lots of
     issues, so has been revised to no longer perform any compilation by
     establishing specific methods on :class:`.FunctionElement` to handle this
     case, as SQL functions are the only use case that it came into play. An
     effect of this behavior is that an unlabeled column expression with no
     derivable name will be given an arbitrary label starting with the prefix
     ``"_no_label"`` in the ``.c`` collection of a subquery; these were
     previously being represented either as the generic stringification of that
     expression, or as an internal symbol.

 .. change::
     :tags: usecase, orm
     :ticketS: 6301

     Altered some of the behavior repaired in :ticket:`6232` where the
     ``immediateload`` loader strategy no longer goes into recursive loops; the
     modification is that an eager load (joinedload, selectinload, or
     subqueryload) from A->bs->B which then states ``immediateload`` for a
     simple manytoone B->a->A that's in the identity map will populate the B->A,
     so that this attribute is back-populated when the collection of A/A.bs are
     loaded. This allows the objects to be functional when detached.


.. changelog::

1.4.9

:released: April 17, 2021

 .. change::
     :tags: bug, sql, regression
     :tickets: 6290

     Fixed regression where an empty in statement on a tuple would result
     in an error when compiled with the option ``literal_binds=True``.

 .. change::
     :tags: bug, regression, orm, performance, sql
     :tickets: 6304

     Fixed a critical performance issue where the traversal of a
     :func:`_sql.select` construct would traverse a repetitive product of the
     represented FROM clauses as they were each referred towards by columns in
     the columns clause; for a series of nested subqueries with lots of columns
     this could cause a large delay and significant memory growth. This
     traversal is used by a wide variety of SQL and ORM functions, including by
     the ORM :class:`_orm.Session` when it's configured to have
     "table-per-bind", which while this is not a common use case, it seems to be
     what Flask-SQLAlchemy is hardcoded as using, so the issue impacts
     Flask-SQLAlchemy users. The traversal has been repaired to uniqify on FROM
     clauses which was effectively what would happen implicitly with the pre-1.4
     architecture.

 .. change::
     :tags: bug, postgresql, sql, regression
     :tickets: 6303

     Fixed an argument error in the default and PostgreSQL compilers that
     would interfere with an UPDATE..FROM or DELETE..FROM..USING statement
     that was then SELECTed from as a CTE.

 .. change::
     :tags: bug, orm, regression
     :tickets: 6272

     Fixed regression where an attribute that is mapped to a
     :func:`_orm.synonym` could not be used in column loader options such as
     :func:`_orm.load_only`.

 .. change::
     :tags: usecase, orm
     :tickets: 6267

     Established support for :func:`_orm.synoynm` in conjunction with
     hybrid property, assocaitionproxy is set up completely, including that
     synonyms can be established linking to these constructs which work
     fully.   This is a behavior that was semi-explicitly disallowed previously,
     however since it did not fail in every scenario, explicit support
     for assoc proxy and hybrids has been added.


.. changelog::

1.4.8

:released: April 15, 2021

 .. change::
     :tags: change, mypy

     Updated Mypy plugin to only use the public plugin interface of the
     semantic analyzer.

 .. change::
     :tags: bug, mssql, regression
     :tickets: 6265

     Fixed an additional regression in the same area as that of :ticket:`6173`,
     :ticket:`6184`, where using a value of 0 for OFFSET in conjunction with
     LIMIT with SQL Server would create a statement using "TOP", as was the
     behavior in 1.3, however due to caching would then fail to respond
     accordingly to other values of OFFSET. If the "0" wasn't first, then it
     would be fine. For the fix, the "TOP" syntax is now only emitted if the
     OFFSET value is omitted entirely, that is, :meth:`_sql.Select.offset` is
     not used. Note that this change now requires that if the "with_ties" or
     "percent" modifiers are used, the statement can't specify an OFFSET of
     zero, it now needs to be omitted entirely.

 .. change::
     :tags: bug, engine

     The :meth:`_engine.Dialect.has_table` method now raises an informative
     exception if a non-Connection is passed to it, as this incorrect behavior
     seems to be common.  This method is not intended for external use outside
     of a dialect.  Please use the :meth:`.Inspector.has_table` method
     or for cross-compatibility with older SQLAlchemy versions, the
     :meth:`_engine.Engine.has_table` method.


 .. change::
     :tags: bug, regression, sql
     :tickets: 6249

     Fixed regression where the :class:`_sql.BindParameter` object would not
     properly render for an IN expression (i.e. using the "post compile" feature
     in 1.4) if the object were copied from either an internal cloning
     operation, or from a pickle operation, and the parameter name contained
     spaces or other special characters.

 .. change::
     :tags: bug, mypy
     :tickets: 6205

     Revised the fix for ``OrderingList`` from version 1.4.7 which was testing
     against the incorrect API.

 .. change::
     :tags: bug, asyncio
     :tickets: 6220

     Fix typo that prevented setting the ``bind`` attribute of an
     :class:`_asyncio.AsyncSession` to the correct value.

 .. change::
     :tags: feature, sql
     :tickets: 3314

     The tuple returned by :attr:`.CursorResult.inserted_primary_key` is now a
     :class:`_result.Row` object with a named tuple interface on top of the
     existing tuple interface.




 .. change::
     :tags: bug, regression, sql, sqlite
     :tickets: 6254

     Fixed regression where the introduction of the INSERT syntax "INSERT...
     VALUES (DEFAULT)" was not supported on some backends that do however
     support "INSERT..DEFAULT VALUES", including SQLite. The two syntaxes are
     now each individually supported or non-supported for each dialect, for
     example MySQL supports "VALUES (DEFAULT)" but not "DEFAULT VALUES".
     Support for Oracle has also been enabled.

 .. change::
     :tags: bug, regression, orm
     :tickets: 6259

     Fixed a cache leak involving the :func:`_orm.with_expression` loader
     option, where the given SQL expression would not be correctly considered as
     part of the cache key.

     Additionally, fixed regression involving the corresponding
     :func:`_orm.query_expression` feature. While the bug technically exists in
     1.3 as well, it was not exposed until 1.4. The "default expr" value of
     ``null()`` would be rendered when not needed, and additionally was also not
     adapted correctly when the ORM rewrites statements such as when using
     joined eager loading. The fix ensures "singleton" expressions like ``NULL``
     and ``true`` aren't "adapted" to refer to columns in ORM statements, and
     additionally ensures that a :func:`_orm.query_expression` with no default
     expression doesn't render in the statement if a
     :func:`_orm.with_expression` isn't used.

 .. change::
     :tags: bug, orm
     :tickets: 6252

     Fixed issue in the new feature of :meth:`_orm.Session.refresh` introduced
     by :ticket:`1763` where eagerly loaded relationships are also refreshed,
     where the ``lazy="raise"`` and ``lazy="raise_on_sql"`` loader strategies
     would interfere with the :func:`_orm.immediateload` loader strategy, thus
     breaking the feature for relationships that were loaded with
     :func:`_orm.selectinload`, :func:`_orm.subqueryload` as well.

.. changelog::

1.4.7

:released: April 9, 2021

 .. change::
     :tags: bug, sql, regression
     :tickets: 6222

     Enhanced the "expanding" feature used for :meth:`_sql.ColumnOperators.in_`
     operations to infer the type of expression from the right hand list of
     elements, if the left hand side does not have any explicit type set up.
     This allows the expression to support stringification among other things.
     In 1.3, "expanding" was not automatically used for
     :meth:`_sql.ColumnOperators.in_` expressions, so in that sense this change
     fixes a behavioral regression.


 .. change::
     :tags: bug, mypy

     Fixed issue in Mypy plugin where the plugin wasn’t inferring the correct
     type for columns of subclasses that don’t directly descend from
     ``TypeEngine``, in particular that of  ``TypeDecorator`` and
     ``UserDefinedType``.

 .. change::
     :tags: bug, orm, regression
     :tickets: 6221

     Fixed regression where the :func:`_orm.subqueryload` loader strategy would
     fail to correctly accommodate sub-options, such as a :func:`_orm.defer`
     option on a column, if the "path" of the subqueryload were more than one
     level deep.


 .. change::
     :tags: bug, sql

     Fixed the "stringify" compiler to support a basic stringification
     of a "multirow" INSERT statement, i.e. one with multiple tuples
     following the VALUES keyword.


 .. change::
     :tags: bug, orm, regression
     :tickets: 6211

     Fixed regression where the :func:`_orm.merge_frozen_result` function relied
     upon by the dogpile.caching example was not included in tests and began
     failing due to incorrect internal arguments.

 .. change::
     :tags: bug, engine, regression
     :tickets: 6218

     Fixed up the behavior of the :class:`_result.Row` object when dictionary
     access is used upon it, meaning converting to a dict via ``dict(row)`` or
     accessing members using strings or other objects i.e. ``row["some_key"]``
     works as it would with a dictionary, rather than raising ``TypeError`` as
     would be the case with a tuple, whether or not the C extensions are in
     place. This was originally supposed to emit a 2.0 deprecation warning for
     the "non-future" case using :class:`_result.LegacyRow`, and was to raise
     ``TypeError`` for the "future" :class:`_result.Row` class. However, the C
     version of :class:`_result.Row` was failing to raise this ``TypeError``,
     and to complicate matters, the :meth:`_orm.Session.execute` method now
     returns :class:`_result.Row` in all cases to maintain consistency with the
     ORM result case, so users who didn't have C extensions installed would
     see different behavior in this one case for existing pre-1.4 style
     code.

     Therefore, in order to soften the overall upgrade scheme as most users have
     not been exposed to the more strict behavior of :class:`_result.Row` up
     through 1.4.6, :class:`_result.LegacyRow` and :class:`_result.Row` both
     provide for string-key access as well as support for ``dict(row)``, in all
     cases emitting the 2.0 deprecation warning when ``SQLALCHEMY_WARN_20`` is
     enabled. The :class:`_result.Row` object still uses tuple-like behavior for
     ``__contains__``, which is probably the only noticeable behavioral change
     compared to :class:`_result.LegacyRow`, other than the removal of
     dictionary-style methods ``values()`` and ``items()``.

 .. change::
     :tags: bug, regression, orm
     :tickets: 6233

     Fixed critical regression where the :class:`_orm.Session` could fail to
     "autobegin" a new transaction when a flush occurred without an existing
     transaction in place, implicitly placing the :class:`_orm.Session` into
     legacy autocommit mode which commit the transaction. The
     :class:`_orm.Session` now has a check that will prevent this condition from
     occurring, in addition to repairing the flush issue.

     Additionally, scaled back part of the change made as part of :ticket:`5226`
     which can run autoflush during an unexpire operation, to not actually
     do this in the case of a :class:`_orm.Session` using legacy
     :paramref:`_orm.Session.autocommit` mode, as this incurs a commit within
     a refresh operation.

 .. change::
     :tags: change, tests

     Added a new flag to :class:`.DefaultDialect` called ``supports_schemas``;
     third party dialects may set this flag to ``False`` to disable SQLAlchemy's
     schema-level tests when running the test suite for a third party dialect.

 .. change::
     :tags: bug, regression, schema
     :tickets: 6216

     Fixed regression where usage of a token in the
     :paramref:`_engine.Connection.execution_options.schema_translate_map`
     dictionary which contained special characters such as braces would fail to
     be substituted properly. Use of square bracket characters ``[]`` is now
     explicitly disallowed as these are used as a delimiter character in the
     current implementation.

 .. change::
     :tags: bug, regression, orm
     :tickets: 6215

     Fixed regression where the ORM compilation scheme would assume the function
     name of a hybrid property would be the same as the attribute name in such a
     way that an ``AttributeError`` would be raised, when it would attempt to
     determine the correct name for each element in a result tuple. A similar
     issue exists in 1.3 but only impacts the names of tuple rows. The fix here
     adds a check that the hybrid's function name is actually present in the
     ``__dict__`` of the class or its superclasses before assigning this name;
     otherwise, the hybrid is considered to be "unnamed" and ORM result tuples
     will use the naming scheme of the underlying expression.

 .. change::
     :tags: bug, orm, regression
     :tickets: 6232

     Fixed critical regression caused by the new feature added as part of
     :ticket:`1763`, eager loaders are invoked on unexpire operations. The new
     feature makes use of the "immediateload" eager loader strategy as a
     substitute for a collection loading strategy, which unlike the other
     "post-load" strategies was not accommodating for recursive invocations
     between mutually-dependent relationships, leading to recursion overflow
     errors.


.. changelog::

1.4.6

:released: April 6, 2021

 .. change::
     :tags: bug, sql, regression, oracle, mssql
     :tickets: 6202

     Fixed further regressions in the same area as that of :ticket:`6173` released in
     1.4.5, where a "postcompile" parameter, again most typically those used for
     LIMIT/OFFSET rendering in Oracle and SQL Server, would fail to be processed
     correctly if the same parameter rendered in multiple places in the
     statement.



 .. change::
     :tags: bug, orm, regression
     :tickets: 6203

     Fixed regression where a deprecated form of :meth:`_orm.Query.join` were
     used, passing a series of entities to join from without any ON clause in a
     single :meth:`_orm.Query.join` call, would fail to function correctly.

 .. change::
     :tags: bug, mypy
     :tickets: 6147

     Applied a series of refactorings and fixes to accommodate for Mypy
     "incremental" mode across multiple files, which previously was not taken
     into account. In this mode the Mypy plugin has to accommodate Python
     datatypes expressed in other files coming in with less information than
     they have on a direct run.

     Additionally, a new decorator :func:`_orm.declarative_mixin` is added,
     which is necessary for the Mypy plugin to be able to definifitely identify
     a Declarative mixin class that is otherwise not used inside a particular
     Python file.

     .. seealso::

         :ref:`mypy_declarative_mixins`


 .. change::
     :