From: Mike Bayer <mike_mp@zzzcomputing.com>
Date: Thu, 7 Mar 2019 14:54:45 +0000 (-0500)
Subject: Add documentation section for cascade_scalar_deletes
X-Git-Tag: rel_1_3_1~5
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e6d0963040b6043bfb89d1e72958c158b830ada9;p=thirdparty%2Fsqlalchemy%2Fsqlalchemy.git

Add documentation section for cascade_scalar_deletes

Change-Id: I56825652e0608862472bc594fc6c2b12ed5cc16f
References: #4534
---

diff --git a/doc/build/orm/extensions/associationproxy.rst b/doc/build/orm/extensions/associationproxy.rst
index e32bb1d492..5670a787df 100644
--- a/doc/build/orm/extensions/associationproxy.rst
+++ b/doc/build/orm/extensions/associationproxy.rst
@@ -494,6 +494,59 @@ be used for querying::
             join(uka, User.keywords.local_attr).\
             join(ka, User.keywords.remote_attr)
 
+.. _cascade_scalar_deletes:
+
+Cascading Scalar Deletes
+------------------------
+
+.. versionadded:: 1.3
+
+Given a mapping as::
+
+    class A(Base):
+        __tablename__ = 'test_a'
+        id = Column(Integer, primary_key=True)
+        ab = relationship(
+            'AB', backref='a', uselist=False)
+        b = association_proxy(
+            'ab', 'b', creator=lambda b: AB(b=b),
+            cascade_scalar_deletes=True)
+
+
+    class B(Base):
+        __tablename__ = 'test_b'
+        id = Column(Integer, primary_key=True)
+        ab = relationship('AB', backref='b', cascade='all, delete-orphan')
+
+
+    class AB(Base):
+        __tablename__ = 'test_ab'
+        a_id = Column(Integer, ForeignKey(A.id), primary_key=True)
+        b_id = Column(Integer, ForeignKey(B.id), primary_key=True)
+
+An assigment to ``A.b`` will generate an ``AB`` object::
+
+    a.b = B()
+
+The ``A.b`` association is scalar, and includes use of the flag
+:paramref:`.AssociationProxy.cascade_scalar_deletes`.  When set, setting ``A.b``
+to ``None`` will remove ``A.ab`` as well::
+
+    a.b = None
+    assert a.ab is None
+
+When :paramref:`.AssociationProxy.cascade_scalar_deletes` is not set,
+the association object ``a.ab`` above would remain in place.
+
+Note that this is not the behavior for collection-based association proxies;
+in that case, the intermediary association object is always removed when
+members of the proxied collection are removed.  Whether or not the row is
+deleted depends on the relationship cascade setting.
+
+.. seealso::
+
+    :ref:`unitofwork_cascades`
+
 API Documentation
 -----------------
 
diff --git a/lib/sqlalchemy/ext/associationproxy.py b/lib/sqlalchemy/ext/associationproxy.py
index 873145b4e5..ea3b8fadeb 100644
--- a/lib/sqlalchemy/ext/associationproxy.py
+++ b/lib/sqlalchemy/ext/associationproxy.py
@@ -140,6 +140,10 @@ class AssociationProxy(interfaces.InspectionAttrInfo):
 
          .. versionadded:: 1.3
 
+         .. seealso::
+
+            :ref:`cascade_scalar_deletes` - complete usage example
+
         :param getset_factory: Optional.  Proxied attribute access is
           automatically handled by routines that get and set values based on
           the `attr` argument for this proxy.