Module « sqlalchemy.orm »

Fonction column_property - module sqlalchemy.orm

Signature de la fonction column_property

def column_property(*columns, **kwargs) 

Description

column_property.__doc__

Provide a column-level property for use with a mapping.

        Column-based properties can normally be applied to the mapper's
        ``properties`` dictionary using the :class:`_schema.Column`
        element directly.
        Use this function when the given column is not directly present within
        the mapper's selectable; examples include SQL expressions, functions,
        and scalar SELECT queries.

        The :func:`_orm.column_property` function returns an instance of
        :class:`.ColumnProperty`.

        Columns that aren't present in the mapper's selectable won't be
        persisted by the mapper and are effectively "read-only" attributes.

        :param \*cols:
              list of Column objects to be mapped.

        :param active_history=False:
          When ``True``, indicates that the "previous" value for a
          scalar attribute should be loaded when replaced, if not
          already loaded. Normally, history tracking logic for
          simple non-primary-key scalar values only needs to be
          aware of the "new" value in order to perform a flush. This
          flag is available for applications that make use of
          :func:`.attributes.get_history` or :meth:`.Session.is_modified`
          which also need to know
          the "previous" value of the attribute.

        :param comparator_factory: a class which extends
           :class:`.ColumnProperty.Comparator` which provides custom SQL
           clause generation for comparison operations.

        :param group:
            a group name for this property when marked as deferred.

        :param deferred:
              when True, the column property is "deferred", meaning that
              it does not load immediately, and is instead loaded when the
              attribute is first accessed on an instance.  See also
              :func:`~sqlalchemy.orm.deferred`.

        :param doc:
              optional string that will be applied as the doc on the
              class-bound descriptor.

        :param expire_on_flush=True:
            Disable expiry on flush.   A column_property() which refers
            to a SQL expression (and not a single table-bound column)
            is considered to be a "read only" property; populating it
            has no effect on the state of data, and it can only return
            database state.   For this reason a column_property()'s value
            is expired whenever the parent object is involved in a
            flush, that is, has any kind of "dirty" state within a flush.
            Setting this parameter to ``False`` will have the effect of
            leaving any existing value present after the flush proceeds.
            Note however that the :class:`.Session` with default expiration
            settings still expires
            all attributes after a :meth:`.Session.commit` call, however.

        :param info: Optional data dictionary which will be populated into the
            :attr:`.MapperProperty.info` attribute of this object.

        :param raiseload: if True, indicates the column should raise an error
            when undeferred, rather than loading the value.  This can be
            altered at query time by using the :func:`.deferred` option with
            raiseload=False.

            .. versionadded:: 1.4

            .. seealso::

                :ref:`deferred_raiseload`

        .. seealso::

            :ref:`column_property_options` - to map columns while including
            mapping options

            :ref:`mapper_column_property_sql_expressions` - to map SQL
            expressions