Cascade mappers in terms of the instance's mapper

Fixed a (extremely old) bug in cascade_mappers where the
first cascade we do is against the "self" mapper, and not the
one that actually corresponds to the state given. These are
different in the case where we start with a relationship
to a class, and the instance is of a subclass, which itself
can have relationships that aren't on the base mapper.

A pretty severe bug that somehow has avoided the radar
since the beginning.

Change-Id: I512956b9757b07e06f3ca1ccb507a33fb10bed31
Fixes: #3986

3 files changed, 159 insertions, 4 deletions

diff --git a/doc/build/changelog/changelog_11.rst b/doc/build/changelog/changelog_11.rst
index c591b483f..523b66f82 100644
--- a/doc/build/changelog/changelog_11.rst
+++ b/doc/build/changelog/changelog_11.rst
@@ -21,6 +21,16 @@
 .. changelog::
     :version: 1.1.10
 
+    .. change:: 3986
+        :tags: bug, orm
+        :versions: 1.2.0b1
+        :tickets: 3986
+
+        Fixed bug where a cascade such as "delete-orphan" (but others as well)
+        would fail to locate an object linked to a relationship that itself
+        is local to a subclass in an inheritance relationship, thus causing
+        the operation to not take place.
+
     .. change:: 3975
         :tags: bug, oracle
         :versions: 1.2.0b1
diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index 3fdba4482..61a9290c4 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -2689,7 +2689,9 @@ class Mapper(InspectionAttr):
         visited_states = set()
         prp, mpp = object(), object()
 
-        visitables = deque([(deque(self._props.values()), prp,
+        assert state.mapper.isa(self)
+
+        visitables = deque([(deque(state.mapper._props.values()), prp,
                              state, state.dict)])
 
         while visitables:
@@ -2712,9 +2714,13 @@ class Mapper(InspectionAttr):
                     corresponding_dict = iterator.popleft()
                 yield instance, instance_mapper, \
                     corresponding_state, corresponding_dict
-                visitables.append((deque(instance_mapper._props.values()),
-                                   prp, corresponding_state,
-                                   corresponding_dict))
+                visitables.append(
+                    (
+                        deque(instance_mapper._props.values()),
+                        prp, corresponding_state,
+                        corresponding_dict
+                    )
+                )
 
     @_memoized_configured_property
     def _compiled_cache(self):
diff --git a/test/orm/test_cascade.py b/test/orm/test_cascade.py
index f660321c2..55467db4b 100644
--- a/test/orm/test_cascade.py
+++ b/test/orm/test_cascade.py
@@ -3067,3 +3067,142 @@ class PartialFlushTest(fixtures.MappedTest):
         assert p1 in sess.new
         assert c1 not in sess.new
         assert c2 in sess.new
+
+
+class SubclassCascadeTest(fixtures.DeclarativeMappedTest):
+    @classmethod
+    def setup_classes(cls):
+        Base = cls.DeclarativeBasic
+
+        class Company(Base):
+            __tablename__ = 'company'
+            id = Column(Integer, primary_key=True)
+            name = Column(String(50))
+            employees = relationship("Employee", cascade="all, delete-orphan")
+
+        class Employee(Base):
+            __tablename__ = 'employee'
+            id = Column(Integer, primary_key=True)
+            name = Column(String(50))
+            type = Column(String(50))
+            company_id = Column(ForeignKey('company.id'))
+
+            __mapper_args__ = {
+                'polymorphic_identity': 'employee',
+                'polymorphic_on': type
+            }
+
+        class Engineer(Employee):
+            __tablename__ = 'engineer'
+            id = Column(Integer, ForeignKey('employee.id'), primary_key=True)
+            engineer_name = Column(String(30))
+            languages = relationship("Language", cascade="all, delete-orphan")
+
+            __mapper_args__ = {
+                'polymorphic_identity': 'engineer',
+            }
+
+        class MavenBuild(Base):
+            __tablename__ = 'maven_build'
+            id = Column(Integer, primary_key=True)
+            java_language_id = Column(
+                ForeignKey('java_language.id'), nullable=False)
+
+        class Manager(Employee):
+            __tablename__ = 'manager'
+            id = Column(Integer, ForeignKey('employee.id'), primary_key=True)
+            manager_name = Column(String(30))
+
+            __mapper_args__ = {
+                'polymorphic_identity': 'manager',
+            }
+
+        class Language(Base):
+            __tablename__ = 'language'
+            id = Column(Integer, primary_key=True)
+            engineer_id = Column(ForeignKey('engineer.id'), nullable=False)
+            name = Column(String(50))
+            type = Column(String(50))
+
+            __mapper_args__ = {
+                "polymorphic_on": type,
+                "polymorphic_identity": "language"
+            }
+
+        class JavaLanguage(Language):
+            __tablename__ = 'java_language'
+            id = Column(ForeignKey('language.id'), primary_key=True)
+            maven_builds = relationship("MavenBuild",
+                                        cascade="all, delete-orphan")
+
+            __mapper_args__ = {
+                "polymorphic_identity": "java_language"
+            }
+
+    def test_cascade_iterator_polymorphic(self):
+        Company, Employee, Engineer, Language, JavaLanguage, MavenBuild = \
+        self.classes(
+            'Company', 'Employee', 'Engineer', 'Language', 'JavaLanguage',
+            'MavenBuild'
+        )
+
+        obj = Company(
+            employees=[
+                Engineer(
+                    languages=[
+                        JavaLanguage(
+                            name="java",
+                            maven_builds=[MavenBuild()]
+                        )
+                    ],
+
+                )
+            ]
+        )
+        eng = obj.employees[0]
+        lang = eng.languages[0]
+        maven_build = lang.maven_builds[0]
+
+        from sqlalchemy import inspect
+        state = inspect(obj)
+        it = inspect(Company).cascade_iterator("save-update", state)
+        eq_(
+            set([rec[0] for rec in it]),
+            set([eng, maven_build, lang])
+        )
+
+        state = inspect(eng)
+        it = inspect(Employee).cascade_iterator("save-update", state)
+        eq_(
+            set([rec[0] for rec in it]),
+            set([maven_build, lang])
+        )
+
+    def test_delete_orphan_round_trip(self):
+        Company, Employee, Engineer, Language, JavaLanguage, \
+            MavenBuild = self.classes(
+                'Company', 'Employee', 'Engineer', 'Language', 'JavaLanguage',
+                'MavenBuild'
+            )
+
+        obj = Company(
+            employees=[
+                Engineer(
+                    languages=[
+                        JavaLanguage(
+                            name="java",
+                            maven_builds=[MavenBuild()]
+                        )
+                    ],
+
+                )
+            ]
+        )
+        s = Session()
+        s.add(obj)
+        s.commit()
+
+        obj.employees = []
+        s.commit()
+
+        eq_(s.query(Language).count(), 0)
\ No newline at end of file