Sqlalchemy

:released: April 21, 2023

.. change::
:tags: bug, typing
:tickets: 9650

Added typing information for recently added operators
:meth:`.ColumnOperators.icontains`, :meth:`.ColumnOperators.istartswith`,
:meth:`.ColumnOperators.iendswith`, and bitwise operators
:meth:`.ColumnOperators.bitwise_and`, :meth:`.ColumnOperators.bitwise_or`,
:meth:`.ColumnOperators.bitwise_xor`, :meth:`.ColumnOperators.bitwise_not`,
:meth:`.ColumnOperators.bitwise_lshift`
:meth:`.ColumnOperators.bitwise_rshift`. Pull request courtesy Martijn
Pieters.


.. change::
:tags: bug, oracle

Fixed issue where the :class:`_sqltypes.Uuid` datatype could not be used in
an INSERT..RETURNING clause with the Oracle dialect.

.. change::
:tags: usecase, engine
:tickets: 9613

Added :func:`_sa.create_pool_from_url` and
:func:`_asyncio.create_async_pool_from_url` to create
a :class:`_pool.Pool` instance from an input url passed as string
or :class:`_sa.URL`.

.. change::
:tags: bug, engine
:tickets: 9618, 9603

Repaired a major shortcoming which was identified in the
:ref:`engine_insertmanyvalues` performance optimization feature first
introduced in the 2.0 series. This was a continuation of the change in
2.0.9 which disabled the SQL Server version of the feature due to a
reliance in the ORM on apparent row ordering that is not guaranteed to take
place. The fix applies new logic to all "insertmanyvalues" operations,
which takes effect when a new parameter
:paramref:`_dml.Insert.returning.sort_by_parameter_order` on the
:meth:`_dml.Insert.returning` or :meth:`_dml.UpdateBase.return_defaults`
methods, that through a combination of alternate SQL forms, direct
correspondence of client side parameters, and in some cases downgrading to
running row-at-a-time, will apply sorting to each batch of returned rows
using correspondence to primary key or other unique values in each row
which can be correlated to the input data.

Performance impact is expected to be minimal as nearly all common primary
key scenarios are suitable for parameter-ordered batching to be
achieved for all backends other than SQLite, while "row-at-a-time"
mode operates with a bare minimum of Python overhead compared to the very
heavyweight approaches used in the 1.x series. For SQLite, there is no
difference in performance when "row-at-a-time" mode is used.

It's anticipated that with an efficient "row-at-a-time" INSERT with
RETURNING batching capability, the "insertmanyvalues" feature can be later
be more easily generalized to third party backends that include RETURNING
support but not necessarily easy ways to guarantee a correspondence
with parameter order.

.. seealso::

:ref:`engine_insertmanyvalues_returning_order`


.. change::
:tags: bug, mssql
:tickets: 9618, 9603

Restored the :term:`insertmanyvalues` feature for Microsoft SQL Server.
This feature was disabled in version 2.0.9 due to an apparent reliance
on the ordering of RETURNING that is not guaranteed. The architecture of
the "insertmanyvalues" feature has been reworked to accommodate for
specific organizations of INSERT statements and result row handling that
can guarantee the correspondence of returned rows to input records.

.. seealso::

:ref:`engine_insertmanyvalues_returning_order`


.. change::
:tags: usecase, postgresql
:tickets: 9608

Added ``prepared_statement_name_func`` connection argument option in the
asyncpg dialect. This option allows passing a callable used to customize
the name of the prepared statement that will be created by the driver
when executing queries. Pull request courtesy Pavel Sirotkin.

.. seealso::

:ref:`asyncpg_prepared_statement_name`

.. change::
:tags: typing, bug

Updates to the codebase to pass typing with Mypy 1.2.0.

.. change::
:tags: bug, typing
:tickets: 9669

Fixed typing issue where :meth:`_orm.PropComparator.and_` expressions would
not be correctly typed inside of loader options such as
:func:`_orm.selectinload`.

.. change::
:tags: bug, orm
:tickets: 9625

Fixed issue where the :meth:`_orm.declared_attr.directive` modifier was not
correctly honored for subclasses when applied to the ``__mapper_args__``
special method name, as opposed to direct use of
:class:`_orm.declared_attr`. The two constructs should have identical
runtime behaviors.

.. change::
:tags: bug, postgresql
:tickets: 9611

Restored the :paramref:`_postgresql.ENUM.name` parameter as optional in the
signature for :class:`_postgresql.ENUM`, as this is chosen automatically
from a given pep-435 ``Enum`` type.


.. change::
:tags: bug, postgresql
:tickets: 9621

Fixed issue where the comparison for :class:`_postgresql.ENUM` against a
plain string would cast that right-hand side type as VARCHAR, which due to
more explicit casting added to dialects such as asyncpg would produce a
PostgreSQL type mismatch error.


.. change::
:tags: bug, orm
:tickets: 9635

Made an improvement to the :func:`_orm.with_loader_criteria` loader option
to allow it to be indicated in the :meth:`.Executable.options` method of a
top-level statement that is not itself an ORM statement. Examples include
:func:`_sql.select` that's embedded in compound statements such as
:func:`_sql.union`, within an :meth:`_dml.Insert.from_select` construct, as
well as within CTE expressions that are not ORM related at the top level.

.. change::
:tags: bug, orm
:tickets: 9685

Fixed bug in ORM bulk insert feature where additional unnecessary columns
would be rendered in the INSERT statement if RETURNING of individual columns
were requested.

.. change::
:tags: bug, postgresql
:tickets: 9615

Fixed issue that prevented reflection of expression based indexes
with long expressions in PostgreSQL. The expression where erroneously
truncated to the identifier length (that's 63 bytes by default).

.. change::
:tags: usecase, postgresql
:tickets: 9509

Add missing :meth:`_postgresql.Range.intersection` method.
Pull request courtesy Yurii Karabas.

.. change::
:tags: bug, orm
:tickets: 9628

Fixed bug in ORM Declarative Dataclasses where the
:func:`_orm.query_expression` and :func:`_orm.column_property`
constructs, which are documented as read-only constructs in the context of
a Declarative mapping, could not be used with a
:class:`_orm.MappedAsDataclass` class without adding ``init=False``, which
in the case of :func:`_orm.query_expression` was not possible as no
``init`` parameter was included. These constructs have been modified from a
dataclass perspective to be assumed to be "read only", setting
``init=False`` by default and no longer including them in the pep-681
constructor. The dataclass parameters for :func:`_orm.column_property`
``init``, ``default``, ``default_factory``, ``kw_only`` are now deprecated;
these fields don't apply to :func:`_orm.column_property` as used in a
Declarative dataclasses configuration where the construct would be
read-only. Also added read-specific parameter
:paramref:`_orm.query_expression.compare` to
:func:`_orm.query_expression`; :paramref:`_orm.query_expression.repr`
was already present.



.. change::
:tags: bug, orm

Added missing :paramref:`_orm.mapped_column.active_history` parameter
to :func:`_orm.mapped_column` construct.

.. changelog::

:released: April 5, 2023

.. change::
:tags: bug, mssql
:tickets: 9603

The SQLAlchemy "insertmanyvalues" feature which allows fast INSERT of
many rows while also supporting RETURNING is temporarily disabled for
SQL Server. As the unit of work currently relies upon this feature such
that it matches existing ORM objects to returned primary key
identities, this particular use pattern does not work with SQL Server
in all cases as the order of rows returned by "OUTPUT inserted" may not
always match the order in which the tuples were sent, leading to
the ORM making the wrong decisions about these objects in subsequent
operations.

The feature will be re-enabled in an upcoming release and will again
take effect for multi-row INSERT statements, however the unit-of-work's
use of the feature will be disabled, possibly for all dialects, unless
ORM-mapped tables also include a "sentinel" column so that the
returned rows can be referenced back to the original data passed in.


.. change::
:tags: bug, mariadb
:tickets: 9588

Added ``row_number`` as reserved word in MariaDb.

.. change::
:tags: bug, mssql
:tickets: 9586

Changed the bulk INSERT strategy used for SQL Server "executemany" with
pyodbc when ``fast_executemany`` is set to ``True`` by using
``fast_executemany`` / ``cursor.executemany()`` for bulk INSERT that does
not include RETURNING, restoring the same behavior as was used in
SQLAlchemy 1.4 when this parameter is set.

New performance details from end users have shown that ``fast_executemany``
is still much faster for very large datasets as it uses ODBC commands that
can receive all rows in a single round trip, allowing for much larger
datasizes than the batches that can be sent by "insertmanyvalues"
as was implemented for SQL Server.

While this change was made such that "insertmanyvalues" continued to be
used for INSERT that includes RETURNING, as well as if ``fast_executemany``
were not set, due to :ticket:`9603`, the "insertmanyvalues" strategy has
been disabled for SQL Server across the board in any case.

.. changelog::

:released: March 31, 2023

.. change::
:tags: bug, orm
:tickets: 9553

Fixed issue in ORM Annotated Declarative where using a recursive type (e.g.
using a nested Dict type) would result in a recursion overflow in the ORM's
annotation resolution logic, even if this datatype were not necessary to
map the column.

.. change::
:tags: bug, examples

Fixed issue in "versioned history" example where using a declarative base
that is derived from :class:`_orm.DeclarativeBase` would fail to be mapped.
Additionally, repaired the given test suite so that the documented
instructions for running the example using Python unittest now work again.

.. change::
:tags: bug, orm
:tickets: 9550

Fixed issue where the :func:`_orm.mapped_column` construct would raise an
internal error if used on a Declarative mixin and included the
:paramref:`_orm.mapped_column.deferred` parameter.

.. change::
:tags: bug, mysql
:tickets: 9544

Fixed issue where string datatypes such as :class:`_sqltypes.CHAR`,
:class:`_sqltypes.VARCHAR`, :class:`_sqltypes.TEXT`, as well as binary
:class:`_sqltypes.BLOB`, could not be produced with an explicit length of
zero, which has special meaning for MySQL. Pull request courtesy J. Nick
Koston.

.. change::
:tags: bug, orm
:tickets: 9537

Expanded the warning emitted when a plain :func:`_sql.column` object is
present in a Declarative mapping to include any arbitrary SQL expression
that is not declared within an appropriate property type such as
:func:`_orm.column_property`, :func:`_orm.deferred`, etc. These attributes
are otherwise not mapped at all and remain unchanged within the class
dictionary. As it seems likely that such an expression is usually not
what's intended, this case now warns for all such otherwise ignored
expressions, rather than just the :func:`_sql.column` case.

.. change::
:tags: bug, orm
:tickets: 9519

Fixed regression where accessing the expression value of a hybrid property
on a class that was either unmapped or not-yet-mapped (such as calling upon
it within a :func:`_orm.declared_attr` method) would raise an internal
error, as an internal fetch for the parent class' mapper would fail and an
instruction for this failure to be ignored were inadvertently removed in
2.0.

.. change::
:tags: bug, orm
:tickets: 9350

Fields that are declared on Declarative Mixins and then combined with
classes that make use of :class:`_orm.MappedAsDataclass`, where those mixin
fields are not themselves part of a dataclass, now emit a deprecation
warning as these fields will be ignored in a future release, as Python
dataclasses behavior is to ignore these fields. Type checkers will not see
these fields under pep-681.

.. seealso::

:ref:`error_dcmx` - background on rationale

:ref:`orm_declarative_dc_mixins`

.. change::
:tags: bug, postgresql
:tickets: 9511

Fixed critical regression in PostgreSQL dialects such as asyncpg which rely
upon explicit casts in SQL in order for datatypes to be passed to the
driver correctly, where a :class:`.String` datatype would be cast along
with the exact column length being compared, leading to implicit truncation
when comparing a ``VARCHAR`` of a smaller length to a string of greater
length regardless of operator in use (e.g. LIKE, MATCH, etc.). The
PostgreSQL dialect now omits the length from ``VARCHAR`` when rendering
these casts.

.. change::
:tags: bug, util
:tickets: 9487

Implemented missing methods ``copy`` and ``pop`` in
OrderedSet class.

.. change::
:tags: bug, typing
:tickets: 9536

Fixed typing for :func:`_orm.deferred` and :func:`_orm.query_expression`
to work correctly with 2.0 style mappings.

.. change::
:tags: bug, orm
:tickets: 9526

Fixed issue where the :meth:`_sql.BindParameter.render_literal_execute`
method would fail when called on a parameter that also had ORM annotations
associated with it. In practice, this would be observed as a failure of SQL
compilation when using some combinations of a dialect that uses "FETCH
FIRST" such as Oracle along with a :class:`_sql.Select` construct that uses
:meth:`_sql.Select.limit`, within some ORM contexts, including if the
statement were embedded within a relationship primaryjoin expression.


.. change::
:tags: usecase, orm
:tickets: 9563

Exceptions such as ``TypeError`` and ``ValueError`` raised by Python
dataclasses when making use of the :class:`_orm.MappedAsDataclass` mixin
class or :meth:`_orm.registry.mapped_as_dataclass` decorator are now
wrapped within an :class:`.InvalidRequestError` wrapper along with
informative context about the error message, referring to the Python
dataclasses documentation as the authoritative source of background
information on the cause of the exception.

.. seealso::

:ref:`error_dcte`


.. change::
:tags: bug, orm
:tickets: 9549

Towards maintaining consistency with unit-of-work changes made for
:ticket:`5984` and :ticket:`8862`, both of which disable "lazy='raise'"
handling within :class:`_orm.Session` processes that aren't triggered by
attribute access, the :meth:`_orm.Session.delete` method will now also
disable "lazy='raise'" handling when it traverses relationship paths in
order to process the "delete" and "delete-orphan" cascade rules.
Previously, there was no easy way to generically call
:meth:`_orm.Session.delete` on an object that had "lazy='raise'" set up
such that only the necessary relationships would be loaded. As
"lazy='raise'" is primarily intended to catch SQL loading that emits on
attribute access, :meth:`_orm.Session.delete` is now made to behave like
other :class:`_orm.Session` methods including :meth:`_orm.Session.merge` as
well as :meth:`_orm.Session.flush` along with autoflush.

.. change::
:tags: bug, orm
:tickets: 9564

Fixed issue where an annotation-only :class:`_orm.Mapped` directive could
not be used in a Declarative mixin class, without that attribute attempting
to take effect for single- or joined-inheritance subclasses of mapped
classes that had already mapped that attribute on a superclass, producing
conflicting column errors and/or warnings.


.. change::
:tags: bug, orm, typing
:tickets: 9514

Properly type :paramref:`_dml.Insert.from_select.names` to accept
a list of string or columns or mapped attributes.

.. changelog::

:released: March 18, 2023

.. change::
:tags: usecase, postgresql
:tickets: 9416

Added new PostgreSQL type :class:`_postgresql.CITEXT`. Pull request
courtesy Julian David Rath.

.. change::
:tags: bug, typing
:tickets: 9502

Fixed typing issue where :func:`_orm.composite` would not allow an
arbitrary callable as the source of the composite class.

.. change::
:tags: usecase, postgresql
:tickets: 9442

Modifications to the base PostgreSQL dialect to allow for better integration with the
sqlalchemy-redshift third party dialect for SQLAlchemy 2.0. Pull request courtesy
matthewgdv.

.. changelog::

:released: March 13, 2023

.. change::
:tags: bug, sql, regression
:tickets: 9461

Fixed regression where the fix for :ticket:`8098`, which was released in
the 1.4 series and provided a layer of concurrency-safe checks for the
lambda SQL API, included additional fixes in the patch that failed to be
applied to the main branch. These additional fixes have been applied.

.. change::
:tags: bug, typing
:tickets: 9451

Fixed typing issue where :meth:`.ColumnElement.cast` did not allow a
:class:`.TypeEngine` argument independent of the type of the
:class:`.ColumnElement` itself, which is the purpose of
:meth:`.ColumnElement.cast`.

.. change::
:tags: bug, orm
:tickets: 9460

Fixed bug where the "active history" feature was not fully
implemented for composite attributes, making it impossible to receive
events that included the "old" value. This seems to have been the case
with older SQLAlchemy versions as well, where "active_history" would
be propagated to the underlying column-based attributes, but an event
handler listening to the composite attribute itself would not be given
the "old" value being replaced, even if the composite() were set up
with active_history=True.

Additionally, fixed a regression that's local to 2.0 which disallowed
active_history on composite from being assigned to the impl with
``attr.impl.active_history=True``.


.. change::
:tags: bug, oracle
:tickets: 9459

Fixed reflection bug where Oracle "name normalize" would not work correctly
for reflection of symbols that are in the "PUBLIC" schema, such as
synonyms, meaning the PUBLIC name could not be indicated as lower case on
the Python side for the :paramref:`_schema.Table.schema` argument. Using
uppercase "PUBLIC" would work, but would then lead to awkward SQL queries
including a quoted ``"PUBLIC"`` name as well as indexing the table under
uppercase "PUBLIC", which was inconsistent.

.. change::
:tags: bug, typing

Fixed issues to allow typing tests to pass under Mypy 1.1.1.

.. change::
:tags: bug, sql
:tickets: 9440

Fixed regression where the :func:`_sql.select` construct would not be able
to render if it were given no columns and then used in the context of an
EXISTS, raising an internal exception instead. While an empty "SELECT" is
not typically valid SQL, in the context of EXISTS databases such as
PostgreSQL allow it, and in any case the condition now no longer raises
an internal exception.


.. change::
:tags: bug, orm
:tickets: 9418

Fixed regression involving pickling of Python rows between the cython and
pure Python implementations of :class:`.Row`, which occurred as part of
refactoring code for version 2.0 with typing. A particular constant were
turned into a string based ``Enum`` for the pure Python version of
:class:`.Row` whereas the cython version continued to use an integer
constant, leading to deserialization failures.

.. changelog::

:released: March 5, 2023

.. change::
:tags: bug, orm
:tickets: 9418

Added constructor arguments to the built-in mapping collection types
including :class:`.KeyFuncDict`, :func:`_orm.attribute_keyed_dict`,
:func:`_orm.column_keyed_dict` so that these dictionary types may be
constructed in place given the data up front; this provides further
compatibility with tools such as Python dataclasses ``.asdict()`` which
relies upon invoking these classes directly as ordinary dictionary classes.

.. change::
:tags: bug, orm, regression
:tickets: 9424

Fixed multiple regressions due to :ticket:`8372`, involving
:func:`_orm.attribute_mapped_collection` (now called
:func:`_orm.attribute_keyed_dict`).

First, the collection was no longer usable with "key" attributes that were
not themselves ordinary mapped attributes; attributes linked to descriptors
and/or association proxy attributes have been fixed.

Second, if an event or other operation needed access to the "key" in order
to populate the dictionary from an mapped attribute that was not
loaded, this also would raise an error inappropriately, rather than
trying to load the attribute as was the behavior in 1.4. This is also
fixed.

For both cases, the behavior of :ticket:`8372` has been expanded.
:ticket:`8372` introduced an error that raises when the derived key that
would be used as a mapped dictionary key is effectively unassigned. In this
change, a warning only is emitted if the effective value of the ".key"
attribute is ``None``, where it cannot be unambiguously determined if this
``None`` was intentional or not. ``None`` will be not supported as mapped
collection dictionary keys going forward (as it typically refers to NULL
which means "unknown"). Setting
:paramref:`_orm.attribute_keyed_dict.ignore_unpopulated_attribute` will now
cause such ``None`` keys to be ignored as well.

.. change::
:tags: engine, performance
:tickets: 9343

A small optimization to the Cython implementation of :class:`.Result`
using a cdef for a particular int value to avoid Python overhead. Pull
request courtesy Matus Valo.


.. change::
:tags: bug, mssql
:tickets: 9414

Fixed issue in the new :class:`.Uuid` datatype which prevented it from
working with the pymssql driver. As pymssql seems to be maintained again,
restored testing support for pymssql.

.. change::
:tags: bug, mssql

Tweaked the pymssql dialect to take better advantage of
RETURNING for INSERT statements in order to retrieve last inserted primary
key values, in the same way as occurs for the mssql+pyodbc dialect right
now.

.. change::
:tags: bug, orm

Identified that the ``sqlite`` and ``mssql+pyodbc`` dialects are now
compatible with the SQLAlchemy ORM's "versioned rows" feature, since
SQLAlchemy now computes rowcount for a RETURNING statement in this specific
case by counting the rows returned, rather than relying upon
``cursor.rowcount``. In particular, the ORM versioned rows use case
(documented at :ref:`mapper_version_counter`) should now be fully
supported with the SQL Server pyodbc dialect.


.. change::
:tags: bug, postgresql
:tickets: 9349

Fixed issue in PostgreSQL :class:`_postgresql.ExcludeConstraint` where
literal values were being compiled as bound parameters and not direct
inline values as is required for DDL.

.. change::
:tags: bug, typing

Fixed bug where the :meth:`_engine.Connection.scalars` method was not typed
as allowing a multiple-parameters list, which is now supported using
insertmanyvalues operations.

.. change::
:tags: bug, typing
:tickets: 9376

Improved typing for the mapping passed to :meth:`.Insert.values` and
:meth:`.Update.values` to be more open-ended about collection type, by
indicating read-only ``Mapping`` instead of writeable ``Dict`` which would
error out on too limited of a key type.

.. change::
:tags: schema

Validate that when provided the :paramref:`_schema.MetaData.schema`
argument of :class:`_schema.MetaData` is a string.

.. change::
:tags: typing, usecase
:tickets: 9338

Exported the type returned by
:meth:`_orm.scoped_session.query_property` using a new public type
:class:`.orm.QueryPropertyDescriptor`.

.. change::
:tags: bug, mysql, postgresql
:tickets: 5648

The support for pool ping listeners to receive exception events via the
:meth:`.DialectEvents.handle_error` event added in 2.0.0b1 for
:ticket:`5648` failed to take into account dialect-specific ping routines
such as that of MySQL and PostgreSQL. The dialect feature has been reworked
so that all dialects participate within event handling. Additionally,
a new boolean element :attr:`.ExceptionContext.is_pre_ping` is added
which identifies if this operation is occurring within the pre-ping
operation.

For this release, third party dialects which implement a custom
:meth:`_engine.Dialect.do_ping` method can opt in to the newly improved
behavior by having their method no longer catch exceptions or check
exceptions for "is_disconnect", instead just propagating all exceptions
outwards. Checking the exception for "is_disconnect" is now done by an
enclosing method on the default dialect, which ensures that the event hook
is invoked for all exception scenarios before testing the exception as a
"disconnect" exception. If an existing ``do_ping()`` method continues to
catch exceptions and check "is_disconnect", it will continue to work as it
did previously, but ``handle_error`` hooks will not have access to the
exception if it isn't propagated outwards.

.. change::
:tags: bug, ext
:tickets: 9367

Fixed issue in automap where calling :meth:`_automap.AutomapBase.prepare`
from a specific mapped class, rather than from the
:class:`_automap.AutomapBase` directly, would not use the correct base
class when automap detected new tables, instead using the given class,
leading to mappers trying to configure inheritance. While one should
normally call :meth:`_automap.AutomapBase.prepare` from the base in any
case, it shouldn't misbehave that badly when called from a subclass.


.. change::
:tags: bug, sqlite, regression
:tickets: 9379

Fixed regression for SQLite connections where use of the ``deterministic``
parameter when establishing database functions would fail for older SQLite
versions, those prior to version 3.8.3. The version checking logic has been
improved to accommodate for this case.

.. change::
:tags: bug, typing
:tickets: 9391

Added missing init overload to the :class:`_types.Numeric` type object so
that pep-484 type checkers may properly resolve the complete type, deriving
from the :paramref:`_types.Numeric.asdecimal` parameter whether ``Decimal``
or ``float`` objects will be represented.

.. change::
:tags: bug, typing
:tickets: 9398

Fixed typing bug where :meth:`_sql.Select.from_statement` would not accept
:func:`_sql.text` or :class:`.TextualSelect` objects as a valid type.
Additionally repaired the :class:`.TextClause.columns` method to have a
return type, which was missing.

.. change::
:tags: bug, orm declarative
:tickets: 9332

Fixed issue where new :paramref:`_orm.mapped_column.use_existing_column`
feature would not work if the two same-named columns were mapped under
attribute names that were differently-named from an explicit name given to
the column itself. The attribute names can now be differently named when
using this parameter.

.. change::
:tags: bug, orm
:tickets: 9373

Added support for the :paramref:`_orm.Mapper.polymorphic_load` parameter to
be applied to each mapper in an inheritance hierarchy more than one level
deep, allowing columns to load for all classes in the hierarchy that
indicate ``"selectin"`` using a single statement, rather than ignoring
elements on those intermediary classes that nonetheless indicate they also
would participate in ``"selectin"`` loading and were not part of the
base-most SELECT statement.

.. change::
:tags: bug, orm
:tickets: 8853, 9335

Continued the fix for :ticket:`8853`, allowing the :class:`_orm.Mapped`
name to be fully qualified regardless of whether or not
``from __annotations__ import future`` were present. This issue first fixed
in 2.0.0b3 confirmed that this case worked via the test suite, however the
test suite apparently was not testing the behavior for the name
:class:`_orm.Mapped` not being locally present at all; string resolution
has been updated to ensure the :class:`_orm.Mapped` symbol is locatable as
applies to how the ORM uses these functions.

.. change::
:tags: bug, typing
:tickets: 9340

Fixed typing issue where :func:`_orm.with_polymorphic` would not
record the class type correctly.

.. change::
:tags: bug, ext, regression
:tickets: 9380

Fixed regression caused by typing added to ``sqlalchemy.ext.mutable`` for
:ticket:`8667`, where the semantics of the ``.pop()`` method changed such
that the method was non-working. Pull request courtesy Nils Philippsen.

.. change::
:tags: bug, sql, regression
:tickets: 9390

Restore the :func:`.nullslast` and :func:`.nullsfirst` legacy functions
into the ``sqlalchemy`` import namespace. Previously, the newer
:func:`.nulls_last` and :func:`.nulls_first` functions were available, but
the legacy ones were inadvertently removed.

.. change::
:tags: bug, postgresql
:tickets: 9401

Fixed issue where the PostgreSQL :class:`_postgresql.ExcludeConstraint`
construct would not be copyable within operations such as
:meth:`_schema.Table.to_metadata` as well as within some Alembic scenarios,
if the constraint contained textual expression elements.

.. change::
:tags: bug, engine
:tickets: 9423

Fixed bug where :class:`_engine.Row` objects could not be reliably unpickled
across processes due to an accidental reliance on an unstable hash value.

.. changelog::