Classe « Query »

Méthode sqlalchemy.orm.Query.count

Signature de la méthode count

def count(self) 

Description

count.__doc__

Return a count of rows this the SQL formed by this :class:`Query`
        would return.

        This generates the SQL for this Query as follows::

            SELECT count(1) AS count_1 FROM (
                SELECT <rest of query follows...>
            ) AS anon_1

        The above SQL returns a single row, which is the aggregate value
        of the count function; the :meth:`_query.Query.count`
        method then returns
        that single integer value.

        .. warning::

            It is important to note that the value returned by
            count() is **not the same as the number of ORM objects that this
            Query would return from a method such as the .all() method**.
            The :class:`_query.Query` object,
            when asked to return full entities,
            will **deduplicate entries based on primary key**, meaning if the
            same primary key value would appear in the results more than once,
            only one object of that primary key would be present.  This does
            not apply to a query that is against individual columns.

            .. seealso::

                :ref:`faq_query_deduplicating`

                :ref:`orm_tutorial_query_returning`

        For fine grained control over specific columns to count, to skip the
        usage of a subquery or otherwise control of the FROM clause, or to use
        other aggregate functions, use :attr:`~sqlalchemy.sql.expression.func`
        expressions in conjunction with :meth:`~.Session.query`, i.e.::

            from sqlalchemy import func

            # count User records, without
            # using a subquery.
            session.query(func.count(User.id))

            # return count of user "id" grouped
            # by "name"
            session.query(func.count(User.id)).\
                    group_by(User.name)

            from sqlalchemy import distinct

            # count distinct "name" values
            session.query(func.count(distinct(User.name)))