Class PrimaryKeyConstraint

lib/sqlalchemy/sql/schema.py:5279–5521

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::

class PrimaryKeyConstraint(ColumnCollectionConstraint):
    """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&#x27;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.

    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),