Expire memoizations on setattr/delattr, check in delattr

Fixed bug where declarative would not update the state of the
:class:`.Mapper` as far as what attributes were present, when additional
attributes were added or removed after the mapper attribute collections had
already been called and memoized.  Addtionally, a ``NotImplementedError``
is now raised if a fully mapped attribute (e.g. column, relationship, etc.)
is deleted from a class that is currently mapped, since the mapper will not
function correctly if the attribute has been removed.

Change-Id: Idaca8e0237b31aa1d6564d94c3a179d7dc6b5df9
Fixes: #4133

1 files changed, 64 insertions, 1 deletions

diff --git a/test/ext/declarative/test_basic.py b/test/ext/declarative/test_basic.py
index 5d1655e87..d2dc1a425 100644
--- a/test/ext/declarative/test_basic.py
+++ b/test/ext/declarative/test_basic.py
@@ -2,6 +2,7 @@
 from sqlalchemy.testing import eq_, assert_raises, \
     assert_raises_message, expect_warnings, is_
 from sqlalchemy.ext import declarative as decl
+from sqlalchemy.ext.hybrid import hybrid_property
 from sqlalchemy import exc
 import sqlalchemy as sa
 from sqlalchemy import testing, util
@@ -1768,7 +1769,7 @@ class DeclarativeTest(DeclarativeTestBase):
         class Test(Base):
             __tablename__ = 'test'
             id = Column(Integer, primary_key=True)
-        # MARKMARK
+
         eq_(
             canary.mock_calls,
             [
@@ -1786,6 +1787,68 @@ class DeclarativeTest(DeclarativeTestBase):
 
         eq_(Base.__doc__, MyBase.__doc__)
 
+    def test_delattr_mapped_raises(self):
+        Base = decl.declarative_base()
+
+        class Foo(Base):
+            __tablename__ = 'foo'
+
+            id = Column(Integer, primary_key=True)
+            data = Column(String)
+
+        def go():
+            del Foo.data
+
+        assert_raises_message(
+            NotImplementedError,
+            "Can't un-map individual mapped attributes on a mapped class.",
+            go
+        )
+
+    def test_delattr_hybrid_fine(self):
+        Base = decl.declarative_base()
+
+        class Foo(Base):
+            __tablename__ = 'foo'
+
+            id = Column(Integer, primary_key=True)
+            data = Column(String)
+
+            @hybrid_property
+            def data_hybrid(self):
+                return self.data
+
+        assert "data_hybrid" in Foo.__mapper__.all_orm_descriptors.keys()
+
+        del Foo.data_hybrid
+
+        assert "data_hybrid" not in Foo.__mapper__.all_orm_descriptors.keys()
+
+        assert not hasattr(Foo, "data_hybrid")
+
+    def test_setattr_hybrid_updates_descriptors(self):
+        Base = decl.declarative_base()
+
+        class Foo(Base):
+            __tablename__ = 'foo'
+
+            id = Column(Integer, primary_key=True)
+            data = Column(String)
+
+        assert "data_hybrid" not in Foo.__mapper__.all_orm_descriptors.keys()
+
+        @hybrid_property
+        def data_hybrid(self):
+            return self.data
+        Foo.data_hybrid = data_hybrid
+        assert "data_hybrid" in Foo.__mapper__.all_orm_descriptors.keys()
+
+        del Foo.data_hybrid
+
+        assert "data_hybrid" not in Foo.__mapper__.all_orm_descriptors.keys()
+
+        assert not hasattr(Foo, "data_hybrid")
+
 
 def _produce_test(inline, stringbased):