Add string arg support for generic relationship

docs/generic_relationship.rst

@@ -47,4 +47,34 @@ Generic relationship is a form of relationship that supports creating a 1 to man
     # Find any events that are bound to users.
     session.query(Event).filter(Event.object.is_type(User)).all()
 
-.. _colour: https://github.com/vaab/colour
+
+Using generic_relationship with abstract base classes
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Generic relationships also allows using string arguments. When using generic_relationship with abstract base classes you need to set up the relationship using declared_attr decorator and string arguments.
+
+
+::
+
+
+    class Building(self.Base):
+        __tablename__ = 'building'
+        id = sa.Column(sa.Integer, primary_key=True)
+
+    class User(self.Base):
+        __tablename__ = 'user'
+        id = sa.Column(sa.Integer, primary_key=True)
+
+    class EventBase(self.Base):
+        __abstract__ = True
+
+        object_type = sa.Column(sa.Unicode(255))
+        object_id = sa.Column(sa.Integer, nullable=False)
+
+        @declared_attr
+        def object(cls):
+            return generic_relationship('object_type', 'object_id')
+
+    class Event(EventBase):
+        __tablename__ = 'event'
+        id = sa.Column(sa.Integer, primary_key=True)

sqlalchemy_utils/generic.py

@@ -1,3 +1,5 @@
+import six
+
 from sqlalchemy.orm.interfaces import MapperProperty, PropComparator
 from sqlalchemy.orm.session import _state_session
 from sqlalchemy.orm import attributes, class_mapper
@@ -86,6 +88,8 @@ class GenericRelationshipProperty(MapperProperty):
     def __init__(self, discriminator, id, doc=None):
         self._discriminator_col = discriminator
         self._id_col = id
+        self._id = None
+        self._discriminator = None
         self.doc = doc
 
         set_creation_order(self)
@@ -98,6 +102,16 @@ class GenericRelationshipProperty(MapperProperty):
 
     def init(self):
         # Resolve columns to attributes.
+        if isinstance(self._discriminator_col, six.string_types):
+            self._discriminator_col = self.parent.columns[
+                self._discriminator_col
+            ]
+
+        if isinstance(self._id_col, six.string_types):
+            self._id_col = self.parent.columns[
+                self._id_col
+            ]
+
         self.discriminator = self._column_to_property(self._discriminator_col)
         self.id = self._column_to_property(self._id_col)
 

tests/test_generic.py

@@ -2,35 +2,14 @@ from __future__ import unicode_literals
 import sqlalchemy as sa
 from tests import TestCase
 from sqlalchemy_utils import generic_relationship
+from sqlalchemy.ext.declarative import declared_attr
 
 
-class TestGenericForiegnKey(TestCase):
+class GenericRelationshipTestCase(TestCase):
-
-    def create_models(self):
-        class Building(self.Base):
-            __tablename__ = 'building'
-            id = sa.Column(sa.Integer, primary_key=True)
-
-        class User(self.Base):
-            __tablename__ = 'user'
-            id = sa.Column(sa.Integer, primary_key=True)
-
-        class Event(self.Base):
-            __tablename__ = 'event'
-            id = sa.Column(sa.Integer, primary_key=True)
-
-            object_type = sa.Column(sa.Unicode(255), name="objectType")
-            object_id = sa.Column(sa.Integer, nullable=False)
-
-            object = generic_relationship(object_type, object_id)
-
-        self.Building = Building
-        self.User = User
-        self.Event = Event
-
     def test_set_as_none(self):
         event = self.Event()
         event.object = None
+        assert event.object is None
 
     def test_set_manual_and_get(self):
         user = self.User()
@@ -128,3 +107,56 @@ class TestGenericForiegnKey(TestCase):
         statement = self.Event.object.is_type(self.User)
         q = self.session.query(self.Event).filter(statement)
         assert q.first() is not None
+
+
+class TestGenericRelationship(GenericRelationshipTestCase):
+    def create_models(self):
+        class Building(self.Base):
+            __tablename__ = 'building'
+            id = sa.Column(sa.Integer, primary_key=True)
+
+        class User(self.Base):
+            __tablename__ = 'user'
+            id = sa.Column(sa.Integer, primary_key=True)
+
+        class Event(self.Base):
+            __tablename__ = 'event'
+            id = sa.Column(sa.Integer, primary_key=True)
+
+            object_type = sa.Column(sa.Unicode(255), name="objectType")
+            object_id = sa.Column(sa.Integer, nullable=False)
+
+            object = generic_relationship(object_type, object_id)
+
+        self.Building = Building
+        self.User = User
+        self.Event = Event
+
+
+class TestGenericRelationshipWithAbstractBase(GenericRelationshipTestCase):
+    def create_models(self):
+        class Building(self.Base):
+            __tablename__ = 'building'
+            id = sa.Column(sa.Integer, primary_key=True)
+
+        class User(self.Base):
+            __tablename__ = 'user'
+            id = sa.Column(sa.Integer, primary_key=True)
+
+        class EventBase(self.Base):
+            __abstract__ = True
+
+            object_type = sa.Column(sa.Unicode(255))
+            object_id = sa.Column(sa.Integer, nullable=False)
+
+            @declared_attr
+            def object(cls):
+                return generic_relationship('object_type', 'object_id')
+
+        class Event(EventBase):
+            __tablename__ = 'event'
+            id = sa.Column(sa.Integer, primary_key=True)
+
+        self.Building = Building
+        self.User = User
+        self.Event = Event