Module « sqlalchemy.orm »

Fonction aliased - module sqlalchemy.orm

Signature de la fonction aliased

def aliased(element, alias=None, name=None, flat=False, adapt_on_names=False) 

Description

aliased.__doc__

Produce an alias of the given element, usually an :class:`.AliasedClass`
    instance.

    E.g.::

        my_alias = aliased(MyClass)

        session.query(MyClass, my_alias).filter(MyClass.id > my_alias.id)

    The :func:`.aliased` function is used to create an ad-hoc mapping of a
    mapped class to a new selectable.  By default, a selectable is generated
    from the normally mapped selectable (typically a :class:`_schema.Table`
    ) using the
    :meth:`_expression.FromClause.alias` method. However, :func:`.aliased`
    can also be
    used to link the class to a new :func:`_expression.select` statement.
    Also, the :func:`.with_polymorphic` function is a variant of
    :func:`.aliased` that is intended to specify a so-called "polymorphic
    selectable", that corresponds to the union of several joined-inheritance
    subclasses at once.

    For convenience, the :func:`.aliased` function also accepts plain
    :class:`_expression.FromClause` constructs, such as a
    :class:`_schema.Table` or
    :func:`_expression.select` construct.   In those cases, the
    :meth:`_expression.FromClause.alias`
    method is called on the object and the new
    :class:`_expression.Alias` object returned.  The returned
    :class:`_expression.Alias` is not
    ORM-mapped in this case.

    :param element: element to be aliased.  Is normally a mapped class,
     but for convenience can also be a :class:`_expression.FromClause`
     element.

    :param alias: Optional selectable unit to map the element to.  This is
     usually used to link the object to a subquery, and should be an aliased
     select construct as one would produce from the
     :meth:`_query.Query.subquery` method or
     the :meth:`_expression.Select.subquery` or
     :meth:`_expression.Select.alias` methods of the :func:`_expression.select`
     construct.

    :param name: optional string name to use for the alias, if not specified
     by the ``alias`` parameter.  The name, among other things, forms the
     attribute name that will be accessible via tuples returned by a
     :class:`_query.Query` object.  Not supported when creating aliases
     of :class:`_sql.Join` objects.

    :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.

    :param adapt_on_names: if True, more liberal "matching" will be used when
     mapping the mapped columns of the ORM entity to those of the
     given selectable - a name-based match will be performed if the
     given selectable doesn't otherwise have a column that corresponds
     to one on the entity.  The use case for this is when associating
     an entity with some derived selectable such as one that uses
     aggregate functions::

        class UnitPrice(Base):
            __tablename__ = 'unit_price'
            ...
            unit_id = Column(Integer)
            price = Column(Numeric)

        aggregated_unit_price = Session.query(
                                    func.sum(UnitPrice.price).label('price')
                                ).group_by(UnitPrice.unit_id).subquery()

        aggregated_unit_price = aliased(UnitPrice,
                    alias=aggregated_unit_price, adapt_on_names=True)

     Above, functions on ``aggregated_unit_price`` which refer to
     ``.price`` will return the
     ``func.sum(UnitPrice.price).label('price')`` column, as it is
     matched on the name "price".  Ordinarily, the "price" function
     wouldn't have any "column correspondence" to the actual
     ``UnitPrice.price`` column as it is not a proxy of the original.