- add explicit warning re: polymorphic_on, cascading is not supported

at this time.  ref #3214

diff --git a/doc/build/orm/inheritance.rst b/doc/build/orm/inheritance.rst
index 642f3420c23ea023915d919502313474aa26f611..9f01a3e24f66380dd12c0cbab5a17a4063c3a6d7 100644 (file)
--- a/doc/build/orm/inheritance.rst
+++ b/doc/build/orm/inheritance.rst
@@ -45,6 +45,12 @@ this column is to act as the **discriminator**, and stores a value
 which indicates the type of object represented within the row. The column may
 be of any datatype, though string and integer are the most common.
 
+.. warning::
+
+   Currently, **only one discriminator column may be set**, typically
+   on the base-most class in the hierarchy. "Cascading" polymorphic columns
+   are not yet supported.
+
 The discriminator column is only needed if polymorphic loading is
 desired, as is usually the case.   It is not strictly necessary that
 it be present directly on the base mapped table, and can instead be defined on a

diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index eaade21ecb9b0720ef54f0bd5a794d1bb1c5b473..2ab239f862c7ccb929ce82ce1fbf099528c8a097 100644 (file)
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -426,6 +426,12 @@ class Mapper(InspectionAttr):
           thus persisting the value to the ``discriminator`` column
           in the database.
 
+          .. warning::
+
+             Currently, **only one discriminator column may be set**, typically
+             on the base-most class in the hierarchy. "Cascading" polymorphic
+             columns are not yet supported.
+
           .. seealso::
 
             :ref:`inheritance_toplevel`