Support extra / single inh criteria with ORM update/delete

The ORM bulk update and delete operations, historically available via the
:meth:`_orm.Query.update` and :meth:`_orm.Query.delete` methods as well as
via the :class:`_dml.Update` and :class:`_dml.Delete` constructs for
:term:`2.0 style` execution, will now automatically accommodate for the
additional WHERE criteria needed for a single-table inheritance
discrminiator.   Joined-table inheritance is still not directly
supported. The new :func:`_orm.with_loader_criteria` construct is also
supported for all mappings with bulk update/delete.

Fixes: #5018
Fixes: #3903
Change-Id: Id90827cc7e2bc713d1255127f908c8e133de9295

1 files changed, 22 insertions, 1 deletions

diff --git a/lib/sqlalchemy/sql/dml.py b/lib/sqlalchemy/sql/dml.py
index a9bccaeff..b7151ac7b 100644
--- a/lib/sqlalchemy/sql/dml.py
+++ b/lib/sqlalchemy/sql/dml.py
@@ -12,6 +12,7 @@ Provide :class:`_expression.Insert`, :class:`_expression.Update` and
 from sqlalchemy.types import NullType
 from . import coercions
 from . import roles
+from .base import _entity_namespace_key
 from .base import _from_objects
 from .base import _generative
 from .base import ColumnCollection
@@ -983,10 +984,30 @@ class DMLWhereBase(object):
         )
 
     def filter(self, *criteria):
-        """A synonym for the :meth:`_dml.DMLWhereBase.where` method."""
+        """A synonym for the :meth:`_dml.DMLWhereBase.where` method.
+
+        .. versionadded:: 1.4
+
+        """
 
         return self.where(*criteria)
 
+    def _filter_by_zero(self):
+        return self.table
+
+    def filter_by(self, **kwargs):
+        r"""apply the given filtering criterion as a WHERE clause
+        to this select.
+
+        """
+        from_entity = self._filter_by_zero()
+
+        clauses = [
+            _entity_namespace_key(from_entity, key) == value
+            for key, value in kwargs.items()
+        ]
+        return self.filter(*clauses)
+
     @property
     def whereclause(self):
         """Return the completed WHERE clause for this :class:`.DMLWhereBase`