Add many_to_one and one_to_many recipes

{{cookiecutter.app_name}}/{{cookiecutter.app_name}}/database.py

@@ -1,10 +1,42 @@
 # -*- coding: utf-8 -*-
 '''Database module, including the SQLAlchemy database object and DB-related
-mixins.
+utilities.
 '''
 
+from sqlalchemy.orm import relationship
+from sqlalchemy.ext.declarative import declared_attr
+
 from .extensions import db
 
+# Helpers from Mike Bayer's atmcraft example app
+# https://bitbucket.org/zzzeek/pycon2014_atmcraft/src/a6d96575bc49?at=master
+def many_to_one(clsname, **kw):
+    """Use an event to build a many-to-one relationship on a class.
+
+    This makes use of the :meth:`.References._reference_table` method
+    to generate a full foreign key relationship to the remote table.
+
+    """
+    @declared_attr
+    def m2o(cls):
+        cls._references((cls.__name__, clsname))
+        return relationship(clsname, **kw)
+    return m2o
+
+def one_to_many(clsname, **kw):
+    """Use an event to build a one-to-many relationship on a class.
+
+    This makes use of the :meth:`.References._reference_table` method
+    to generate a full foreign key relationship from the remote table.
+
+    """
+    @declared_attr
+    def o2m(cls):
+        cls._references((clsname, cls.__name__))
+        return relationship(clsname, **kw)
+    return o2m
+
+
 class CRUDMixin(object):
     """Mixin that adds convenience methods for CRUD (create, read, update, delete)
     operations.