sqlalchemy.sql.schema.PrimaryKeyConstraint

A table-level PRIMARY KEY constraint. The :class:`.PrimaryKeyConstraint` object is present automatically on any :class:`_schema.Table` object; it is assigned a set of :class:`_schema.Column` objects corresponding to those marked with the :paramref:`_schema.Column.primary_key` flag:: >>> my_table = Table('mytable', metadata, ... Column('id', Integer, primary_key=True), ... Column('version_id', Integer, primary_key=True), ... Column('data', String(50)) ... ) >>> my_table.primary_key PrimaryKeyConstraint( Column('id', Integer(), table=<mytable>, primary_key=True, nullable=False), Column('version_id', Integer(), table=<mytable>, primary_key=True, nullable=False) ) The primary key of a :class:`_schema.Table` can also be specified by using a :class:`.PrimaryKeyConstraint` object explicitly; in this mode of usage, the "name" of the constraint can also be specified, as well as other options which may be recognized by dialects:: my_table = Table('mytable', metadata, Column('id', Integer), Column('version_id', Integer), Column('data', String(50)), PrimaryKeyConstraint('id', 'version_id', name='mytable_pk') ) The two styles of column-specification should generally not be mixed. An warning is emitted if the columns present in the :class:`.PrimaryKeyConstraint` don't match the columns that were marked as ``primary_key=True``, if both are present; in this case, the columns are taken strictly from the :class:`.PrimaryKeyConstraint` declaration, and those columns otherwise marked as ``primary_key=True`` are ignored. This behavior is intended to be backwards compatible with previous behavior. .. versionchanged:: 0.9.2 Using a mixture of columns within a :class:`.PrimaryKeyConstraint` in addition to columns marked as ``primary_key=True`` now emits a warning if the lists don't match. The ultimate behavior of ignoring those columns marked with the flag only is currently maintained for backwards compatibility; this warning may raise an exception in a future release. For the use case where specific options are to be specified on the :class:`.PrimaryKeyConstraint`, but the usual style of using ``primary_key=True`` flags is still desirable, an empty :class:`.PrimaryKeyConstraint` may be specified, which will take on the primary key column collection from the :class:`_schema.Table` based on the flags:: my_table = Table('mytable', metadata, Column('id', Integer, primary_key=True), Column('version_id', Integer, primary_key=True), Column('data', String(50)), PrimaryKeyConstraint(name='mytable_pk', mssql_clustered=True) ) .. versionadded:: 0.9.2 an empty :class:`.PrimaryKeyConstraint` may now be specified for the purposes of establishing keyword arguments with the constraint, independently of the specification of "primary key" columns within the :class:`_schema.Table` itself; columns marked as ``primary_key=True`` will be gathered into the empty constraint's column collection.