1.4.20

Released: June 28, 2021

orm

• [orm] [bug] [regression] Fixed regression in ORM regarding an internal reconstitution step for the
  _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.

  References: #6680

• [orm] [bug] [regression] Adjusted _orm.Query.union() and similar set operations to be
  correctly compatible with the new capabilities just added in
  #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 _orm.undefer() option
  to be used at the top level of such a _orm.Query without having to
  apply the option to each of the elements within the UNION.

  References: #6678

• [orm] [bug] 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.

  References: #6538

engine

• [engine] [bug] Fixed an issue in the C extension for the _result.Row class which
  could lead to a memory leak in the unlikely case of a _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 _result.Row implementation to
  accommodate for this case.

  References: #5348

• [engine] [bug] Fixed old issue where a _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.

  References: #6665

sql

• [sql] [usecase] Add a impl parameter to _types.PickleType constructor, allowing
  any arbitary type to be used in place of the default implementation of
  _types.LargeBinary. Pull request courtesy jason3gb.

  References: #6646

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

  References: #6668

schema

• [schema] [bug] Fixed issue where passing None for the value of
  _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.

  References: #6685

mysql

• [mysql] [usecase] 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.

  References: #6659

misc

• [bug] [ext] [regression] Fixed regression in sqlalchemy.ext.automap extension such that the
  use case of creating an explicit mapped class to a table that is also the
  _orm.relationship.secondary element of a
  _orm.relationship() that automap will be generating would emit the
  "overlaps" warnings introduced in 1.4 and discussed at 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.

  References: #6679