: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:`_sql.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::