--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/app/polymodel/LICENSE	Fri Sep 26 19:35:21 2008 +0000
@@ -0,0 +1,22 @@
+The MIT License
+
+Copyright (c) 2008 Andreas Blixt <andreas@blixt.org>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/app/polymodel/__init__.py	Fri Sep 26 19:35:21 2008 +0000
@@ -0,0 +1,120 @@
+#
+# Copyright (c) 2008 Andreas Blixt <andreas@blixt.org>
+# Project homepage: <http://code.google.com/p/blixt/>
+#
+# License: MIT license <http://www.opensource.org/licenses/mit-license.php>
+#
+
+"""Data-related Google App Engine extensions.
+"""
+
+from google.appengine.ext import db
+
+import sys
+
+class Error(Exception):
+    """Base of all exceptions in the blixt.data module."""
+    pass
+
+class PolyModel(db.Model):
+    """An extension to Google App Engine models that improves the support for
+    inheritance.
+
+    Any models extending a model that extends PolyModel will be stored in the
+    datastore as the same kind as the model that extends PolyModel, but with
+    their additional properties. When they are retrieved from the datastore,
+    they will be loaded as the appropiate model class.
+
+    The difference from the Model class is that queries will include models that
+    inherit from the model being queried.
+    """
+    inheritance_line = db.StringListProperty()
+
+    def __init__(self, parent = None, key_name = None, _app = None, **kwds):
+        """Creates a new instance of this polymorphic model.
+
+        Args:
+          parent: Parent instance for this instance or None, indicating a top-
+            level instance.
+          key_name: Name for new model instance.
+          _app: Intentionally undocumented.
+          args: Keyword arguments mapping to properties of model.
+        """
+        if self.__class__ == PolyModel or not isinstance(self, PolyModel):
+            raise Error('Instances of PolyModel must be created through a '
+                        'subclass of PolyModel.')
+
+        line = []
+        for c in self.__class__.__mro__:
+            if c == PolyModel:
+                self.__class__._kind = p
+                break
+            line.append('%s.%s' % (c.__module__, c.__name__))
+            p = c
+
+        kwds['inheritance_line'] = line
+
+        super(PolyModel, self).__init__(parent = parent, key_name = key_name,
+                                        _app = _app, **kwds)
+
+    @classmethod
+    def _kind_type(cls):
+        """Gets the class highest in the model inheritance hierarchy (the class
+        that will be used as the datastore kind.)
+        """
+        p = cls
+
+        for c in cls.__mro__:
+            # The meta-class 'PropertiedClass' calls kind() which leads here.
+            # The variable 'PolyModel' is not assigned until after the meta-
+            # class has finished setting up the class. Therefore, a string
+            # comparison is used instead of a value comparison.
+            if c.__name__ == 'PolyModel': break
+            p = c
+
+        return p
+
+    @classmethod
+    def all(cls):
+        """Returns a query over all instances of this model, as well as the
+        instances of any descendant models, from the datastore.
+
+        Returns:
+          Query that will retrieve all instances from entity collection.
+        """
+        qry = super(PolyModel, cls).all()
+
+        if cls != cls._kind_type():
+            full_name = '%s.%s' % (cls.__module__, cls.__name__)
+            qry.filter('inheritance_line =', full_name)
+
+        return qry
+
+    @classmethod
+    def from_entity(cls, entity):
+        """Converts the entity representation of this model to an instance.
+
+        Converts datastore.Entity instance to an instance of the appropiate
+        class, which can be cls or any descendant thereof.
+
+        Args:
+          entity: Entity loaded directly from datastore.
+
+        Raises:
+          KindError when cls is incorrect model for entity.
+        """
+        if entity.has_key('inheritance_line'):
+            mod_name, cls_name = entity['inheritance_line'][0].rsplit('.', 1)
+            __import__(mod_name)
+            cls = getattr(sys.modules[mod_name], cls_name)
+        return super(PolyModel, cls).from_entity(entity)
+
+    @classmethod
+    def kind(cls):
+        """Returns the datastore kind we use for this model.
+
+        This is the name of the class that is highest up in the inheritance
+        hierarchy of this model.
+        """
+        return cls._kind_type().__name__
+