A warning is emitted when trying to flush an object of an inherited

mapped class where the polymorphic discriminator has been assigned
to a value that is invalid for the class.   [ticket:2750]

2 files changed, 35 insertions, 1 deletions

diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index 7f14d83cb..12d2234d2 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -28,7 +28,7 @@ from .interfaces import MapperProperty, _InspectionAttr, _MappedAttribute
 
 from .util import _INSTRUMENTOR, _class_to_mapper, \
         _state_mapper, class_mapper, \
-        PathRegistry
+        PathRegistry, state_str
 import sys
 properties = util.importlater("sqlalchemy.orm", "properties")
 descriptor_props = util.importlater("sqlalchemy.orm", "descriptor_props")
@@ -1040,6 +1040,8 @@ class Mapper(_InspectionAttr):
                     if self.polymorphic_on is not None:
                         self._set_polymorphic_identity = \
                             mapper._set_polymorphic_identity
+                        self._validate_polymorphic_identity = \
+                            mapper._validate_polymorphic_identity
                     else:
                         self._set_polymorphic_identity = None
                     return
@@ -1050,10 +1052,39 @@ class Mapper(_InspectionAttr):
                 state.get_impl(polymorphic_key).set(state, dict_,
                         state.manager.mapper.polymorphic_identity, None)
 
+            def _validate_polymorphic_identity(mapper, state, dict_):
+                if dict_[polymorphic_key] not in \
+                    mapper._acceptable_polymorphic_identities:
+                    util.warn(
+                                "Flushing object %s with "
+                                "incompatible polymorphic identity %r; the "
+                                "object may not refresh and/or load correctly" % (
+                                        state_str(state),
+                                        dict_[polymorphic_key]
+                                    )
+                            )
+
             self._set_polymorphic_identity = _set_polymorphic_identity
+            self._validate_polymorphic_identity = _validate_polymorphic_identity
         else:
             self._set_polymorphic_identity = None
 
+
+    _validate_polymorphic_identity = None
+
+    @_memoized_configured_property
+    def _acceptable_polymorphic_identities(self):
+        identities = set()
+
+        stack = deque([self])
+        while stack:
+            item = stack.popleft()
+            if item.mapped_table is self.mapped_table:
+                identities.add(item.polymorphic_identity)
+                stack.extend(item._inheriting_mappers)
+
+        return identities
+
     def _adapt_inherited_property(self, key, prop, init):
         if not self.concrete:
             self._configure_property(key, prop, init=False, setparent=False)
diff --git a/lib/sqlalchemy/orm/persistence.py b/lib/sqlalchemy/orm/persistence.py
index a773786c4..944623b07 100644
--- a/lib/sqlalchemy/orm/persistence.py
+++ b/lib/sqlalchemy/orm/persistence.py
@@ -150,6 +150,9 @@ def _organize_states_for_save(base_mapper, states, uowtransaction):
         else:
             mapper.dispatch.before_update(mapper, connection, state)
 
+        if mapper._validate_polymorphic_identity:
+            mapper._validate_polymorphic_identity(mapper, state, dict_)
+
         # detect if we have a "pending" instance (i.e. has
         # no instance_key attached to it), and another instance
         # with the same identity key already exists as persistent.