Module « sqlalchemy.orm »

Fonction with_polymorphic - module sqlalchemy.orm

Signature de la fonction with_polymorphic

def with_polymorphic(base, classes, selectable=False, flat=False, polymorphic_on=None, aliased=False, innerjoin=False, _use_mapper_path=False, _existing_alias=None) 

Description

with_polymorphic.__doc__

Produce an :class:`.AliasedClass` construct which specifies
    columns for descendant mappers of the given base.

    Using this method will ensure that each descendant mapper's
    tables are included in the FROM clause, and will allow filter()
    criterion to be used against those tables.  The resulting
    instances will also have those columns already loaded so that
    no "post fetch" of those columns will be required.

    .. seealso::

        :ref:`with_polymorphic` - full discussion of
        :func:`_orm.with_polymorphic`.

    :param base: Base class to be aliased.

    :param classes: a single class or mapper, or list of
        class/mappers, which inherit from the base class.
        Alternatively, it may also be the string ``'*'``, in which case
        all descending mapped classes will be added to the FROM clause.

    :param aliased: when True, the selectable will be aliased.   For a
        JOIN, this means the JOIN will be SELECTed from inside of a subquery
        unless the :paramref:`_orm.with_polymorphic.flat` flag is set to
        True, which is recommended for simpler use cases.

    :param flat: Boolean, will be passed through to the
     :meth:`_expression.FromClause.alias` call so that aliases of
     :class:`_expression.Join` objects will alias the individual tables
     inside the join, rather than creating a subquery.  This is generally
     supported by all modern databases with regards to right-nested joins
     and generally produces more efficient queries.  Setting this flag is
     recommended as long as the resulting SQL is functional.

    :param selectable: a table or subquery that will
        be used in place of the generated FROM clause. This argument is
        required if any of the desired classes use concrete table
        inheritance, since SQLAlchemy currently cannot generate UNIONs
        among tables automatically. If used, the ``selectable`` argument
        must represent the full set of tables and columns mapped by every
        mapped class. Otherwise, the unaccounted mapped columns will
        result in their table being appended directly to the FROM clause
        which will usually lead to incorrect results.

    :param polymorphic_on: a column to be used as the "discriminator"
        column for the given selectable. If not given, the polymorphic_on
        attribute of the base classes' mapper will be used, if any. This
        is useful for mappings that don't have polymorphic loading
        behavior by default.

    :param innerjoin: if True, an INNER JOIN will be used.  This should
       only be specified if querying for one specific subtype only