fix: add make_proxy() convenience method for data model Base

src/wuttjamaican/db/model/base.py

@@ -25,19 +25,103 @@ Base Models
 
 .. class:: Base
 
-   This is the base class for all data models.
+   This is the base class for all :term:`data models <data model>` in
+   the :term:`app database`.  You should inherit from this class when
+   defining custom models.
+
+   This class inherits from :class:`WuttaModelBase`.
 """
 
 import sqlalchemy as sa
 from sqlalchemy import orm
+from sqlalchemy.ext.associationproxy import association_proxy
 
 from wuttjamaican.db.util import (naming_convention, ModelBase,
                                   uuid_column, uuid_fk_column)
 
 
+class WuttaModelBase(ModelBase):
+    """
+    Base class for data models, from which :class:`Base` inherits.
+
+    Custom models should inherit from :class:`Base` instead of this
+    class.
+    """
+
+    @classmethod
+    def make_proxy(cls, main_class, extension, name, proxy_name=None):
+        """
+        Convenience method to declare an "association proxy" for the
+        main class, per the params.
+
+        For more info see
+        :doc:`sqlalchemy:orm/extensions/associationproxy`.
+
+        :param main_class: Reference to the "parent" model class, upon
+           which the proxy will be defined.
+
+        :param extension: Attribute name on the main class, which
+           references the extension record.
+
+        :param name: Attribute name on the extension class, which
+           provides the proxied value.
+
+        :param proxy_name: Optional attribute name on the main class,
+           which will reference the proxy.  If not specified, ``name``
+           will be used.
+
+        As a simple example consider this model, which extends the
+        :class:`~wuttjamaican.db.model.auth.User` class.  In
+        particular note the last line which is what we're documenting
+        here::
+
+           import sqlalchemy as sa
+           from sqlalchemy import orm
+           from wuttjamaican.db import model
+
+           class PoserUser(model.Base):
+               \""" Poser extension for User \"""
+               __tablename__ = 'poser_user'
+
+               uuid = model.uuid_column(sa.ForeignKey('user.uuid'), default=None)
+               user = orm.relationship(
+                   model.User,
+                   doc="Reference to the main User record.",
+                   backref=orm.backref(
+                       '_poser',
+                       uselist=False,
+                       cascade='all, delete-orphan',
+                       doc="Reference to the Poser extension record."))
+
+               favorite_color = sa.Column(sa.String(length=100), nullable=False, doc=\"""
+               User's favorite color.
+               \""")
+
+           def __str__(self):
+               return str(self.user)
+
+           # nb. this is the method call
+           PoserUser.make_proxy(model.User, '_poser', 'favorite_color')
+
+        That code defines a ``PoserUser`` model but also defines a
+        ``favorite_color`` attribute on the main ``User`` class, such
+        that it can be used normally::
+
+            user = model.User(username='barney', favorite_color='green')
+            session.add(user)
+
+            user = session.query(model.User).filter_by(username='bambam').one()
+            print(user.favorite_color)
+        """
+        proxy = association_proxy(
+            extension, proxy_name or name,
+            creator=lambda value: cls(**{name: value}))
+        setattr(main_class, name, proxy)
+
+
 metadata = sa.MetaData(naming_convention=naming_convention)
 
-Base = orm.declarative_base(metadata=metadata, cls=ModelBase)
+Base = orm.declarative_base(metadata=metadata, cls=WuttaModelBase)
 
 
 class Setting(Base):

tests/db/model/test_base.py

@@ -3,12 +3,34 @@
 from unittest import TestCase
 
 try:
+    import sqlalchemy as sa
+    from sqlalchemy import orm
     from wuttjamaican.db.model import base as mod
     from wuttjamaican.db.model.auth import User
 except ImportError:
     pass
 else:
 
+
+    class MockUser(mod.Base):
+        __tablename__ = 'mock_user'
+        uuid = mod.uuid_column(sa.ForeignKey('user.uuid'), default=False)
+        user = orm.relationship(
+            User,
+            backref=orm.backref('_mock', uselist=False, cascade='all, delete-orphan'))
+        favorite_color = sa.Column(sa.String(length=100), nullable=False)
+
+
+    class TestWuttaModelBase(TestCase):
+
+        def test_make_proxy(self):
+            self.assertFalse(hasattr(User, 'favorite_color'))
+            MockUser.make_proxy(User, '_mock', 'favorite_color')
+            self.assertTrue(hasattr(User, 'favorite_color'))
+            user = User(favorite_color='green')
+            self.assertEqual(user.favorite_color, 'green')
+
+
     class TestSetting(TestCase):
 
         def test_basic(self):
@@ -17,6 +39,7 @@ else:
             setting.name = 'foo'
             self.assertEqual(str(setting), "foo")
 
+
     class TestPerson(TestCase):
 
         def test_basic(self):