From da6570bf082620205737c82cd7deb7185daaf538 Mon Sep 17 00:00:00 2001
From: Malcolm Tredinnick <malcolm.tredinnick@gmail.com>
Date: Sun, 17 Feb 2008 18:47:57 +0000
Subject: [PATCH] queryset-refactor: Model inheritance support.

This adds both types of model inheritance: abstract base classes (ABCs) and
multi-table inheritance. See the documentation and tests / examples for details.

Still a few known bugs here, so don't file tickets (I know about them). Not
quite ready for prime-time usage, but it mostly works as expected.


git-svn-id: http://code.djangoproject.com/svn/django/branches/queryset-refactor@7126 bcc190cf-cafb-0310-a4f2-bffc1f526a37
---
 django/core/management/sql.py                |  16 +-
 django/core/management/validation.py         |  23 +-
 django/db/models/base.py                     | 127 +++++----
 django/db/models/fields/__init__.py          |  26 +-
 django/db/models/fields/related.py           |   7 +-
 django/db/models/manager.py                  |   4 +-
 django/db/models/options.py                  | 260 +++++++++++++++----
 django/db/models/sql/query.py                |  26 +-
 docs/model-api.txt                           |  99 +++++++
 tests/modeltests/model_inheritance/models.py | 157 ++++++++++-
 10 files changed, 607 insertions(+), 138 deletions(-)

diff --git a/django/core/management/sql.py b/django/core/management/sql.py
index 15bffce26b..9e606a745c 100644
--- a/django/core/management/sql.py
+++ b/django/core/management/sql.py
@@ -26,7 +26,7 @@ def django_table_list(only_existing=False):
     for app in models.get_apps():
         for model in models.get_models(app):
             tables.append(model._meta.db_table)
-            tables.extend([f.m2m_db_table() for f in model._meta.many_to_many])
+            tables.extend([f.m2m_db_table() for f in model._meta.local_many_to_many])
     if only_existing:
         existing = table_list()
         tables = [t for t in tables if t in existing]
@@ -54,12 +54,12 @@ def sequence_list():
 
     for app in apps:
         for model in models.get_models(app):
-            for f in model._meta.fields:
+            for f in model._meta.local_fields:
                 if isinstance(f, models.AutoField):
                     sequence_list.append({'table': model._meta.db_table, 'column': f.column})
                     break # Only one AutoField is allowed per model, so don't bother continuing.
 
-            for f in model._meta.many_to_many:
+            for f in model._meta.local_many_to_many:
                 sequence_list.append({'table': f.m2m_db_table(), 'column': None})
 
     return sequence_list
@@ -147,7 +147,7 @@ def sql_delete(app, style):
         if cursor and table_name_converter(model._meta.db_table) in table_names:
             # The table exists, so it needs to be dropped
             opts = model._meta
-            for f in opts.fields:
+            for f in opts.local_fields:
                 if f.rel and f.rel.to not in to_delete:
                     references_to_delete.setdefault(f.rel.to, []).append( (model, f) )
 
@@ -179,7 +179,7 @@ def sql_delete(app, style):
     # Output DROP TABLE statements for many-to-many tables.
     for model in app_models:
         opts = model._meta
-        for f in opts.many_to_many:
+        for f in opts.local_many_to_many:
             if isinstance(f.rel, generic.GenericRel):
                 continue
             if cursor and table_name_converter(f.m2m_db_table()) in table_names:
@@ -256,7 +256,7 @@ def sql_model_create(model, style, known_models=set()):
     pending_references = {}
     qn = connection.ops.quote_name
     inline_references = connection.features.inline_fk_references
-    for f in opts.fields:
+    for f in opts.local_fields:
         col_type = f.db_type()
         tablespace = f.db_tablespace or opts.db_tablespace
         if col_type is None:
@@ -351,7 +351,7 @@ def many_to_many_sql_for_model(model, style):
     final_output = []
     qn = connection.ops.quote_name
     inline_references = connection.features.inline_fk_references
-    for f in opts.many_to_many:
+    for f in opts.local_many_to_many:
         if not isinstance(f.rel, generic.GenericRel):
             tablespace = f.db_tablespace or opts.db_tablespace
             if tablespace and connection.features.supports_tablespaces and connection.features.autoindexes_primary_keys:
@@ -458,7 +458,7 @@ def sql_indexes_for_model(model, style):
     output = []
 
     qn = connection.ops.quote_name
-    for f in model._meta.fields:
+    for f in model._meta.local_fields:
         if f.db_index and not ((f.primary_key or f.unique) and connection.features.autoindexes_primary_keys):
             unique = f.unique and 'UNIQUE ' or ''
             tablespace = f.db_tablespace or model._meta.db_tablespace
diff --git a/django/core/management/validation.py b/django/core/management/validation.py
index fc3a7162a1..f5e4f7fc70 100644
--- a/django/core/management/validation.py
+++ b/django/core/management/validation.py
@@ -32,7 +32,7 @@ def get_validation_errors(outfile, app=None):
         opts = cls._meta
 
         # Do field-specific validation.
-        for f in opts.fields:
+        for f in opts.local_fields:
             if f.name == 'id' and not f.primary_key and opts.pk.name == 'id':
                 e.add(opts, '"%s": You can\'t use "id" as a field name, because each model automatically gets an "id" field if none of the fields have primary_key=True. You need to either remove/rename your "id" field or add primary_key=True to a field.' % f.name)
             if f.name.endswith('_'):
@@ -69,8 +69,8 @@ def get_validation_errors(outfile, app=None):
                 if db_version < (5, 0, 3) and isinstance(f, (models.CharField, models.CommaSeparatedIntegerField, models.SlugField)) and f.max_length > 255:
                     e.add(opts, '"%s": %s cannot have a "max_length" greater than 255 when you are using a version of MySQL prior to 5.0.3 (you are using %s).' % (f.name, f.__class__.__name__, '.'.join([str(n) for n in db_version[:3]])))
 
-            # Check to see if the related field will clash with any
-            # existing fields, m2m fields, m2m related objects or related objects
+            # Check to see if the related field will clash with any existing
+            # fields, m2m fields, m2m related objects or related objects
             if f.rel:
                 if f.rel.to not in models.get_models():
                     e.add(opts, "'%s' has relation with model %s, which has not been installed" % (f.name, f.rel.to))
@@ -87,7 +87,7 @@ def get_validation_errors(outfile, app=None):
                         e.add(opts, "Accessor for field '%s' clashes with field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.name, f.name))
                     if r.name == rel_query_name:
                         e.add(opts, "Reverse query name for field '%s' clashes with field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.name, f.name))
-                for r in rel_opts.many_to_many:
+                for r in rel_opts.local_many_to_many:
                     if r.name == rel_name:
                         e.add(opts, "Accessor for field '%s' clashes with m2m field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.name, f.name))
                     if r.name == rel_query_name:
@@ -104,9 +104,10 @@ def get_validation_errors(outfile, app=None):
                         if r.get_accessor_name() == rel_query_name:
                             e.add(opts, "Reverse query name for field '%s' clashes with related field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.get_accessor_name(), f.name))
 
-        for i, f in enumerate(opts.many_to_many):
+        for i, f in enumerate(opts.local_many_to_many):
             # Check to see if the related m2m field will clash with any
-            # existing fields, m2m fields, m2m related objects or related objects
+            # existing fields, m2m fields, m2m related objects or related
+            # objects
             if f.rel.to not in models.get_models():
                 e.add(opts, "'%s' has m2m relation with model %s, which has not been installed" % (f.name, f.rel.to))
                 # it is a string and we could not find the model it refers to
@@ -117,17 +118,17 @@ def get_validation_errors(outfile, app=None):
             rel_opts = f.rel.to._meta
             rel_name = RelatedObject(f.rel.to, cls, f).get_accessor_name()
             rel_query_name = f.related_query_name()
-            # If rel_name is none, there is no reverse accessor.
-            # (This only occurs for symmetrical m2m relations to self).
-            # If this is the case, there are no clashes to check for this field, as
-            # there are no reverse descriptors for this field.
+            # If rel_name is none, there is no reverse accessor (this only
+            # occurs for symmetrical m2m relations to self). If this is the
+            # case, there are no clashes to check for this field, as there are
+            # no reverse descriptors for this field.
             if rel_name is not None:
                 for r in rel_opts.fields:
                     if r.name == rel_name:
                         e.add(opts, "Accessor for m2m field '%s' clashes with field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.name, f.name))
                     if r.name == rel_query_name:
                         e.add(opts, "Reverse query name for m2m field '%s' clashes with field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.name, f.name))
-                for r in rel_opts.many_to_many:
+                for r in rel_opts.local_many_to_many:
                     if r.name == rel_name:
                         e.add(opts, "Accessor for m2m field '%s' clashes with m2m field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.name, f.name))
                     if r.name == rel_query_name:
diff --git a/django/db/models/base.py b/django/db/models/base.py
index 9236207f94..45bb82c3f4 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -1,9 +1,14 @@
+import types
+import sys
+import os
+from itertools import izip
+
 import django.db.models.manipulators
 import django.db.models.manager
 from django.core import validators
 from django.core.exceptions import ObjectDoesNotExist, MultipleObjectsReturned
 from django.db.models.fields import AutoField, ImageField, FieldDoesNotExist
-from django.db.models.fields.related import OneToOneRel, ManyToOneRel
+from django.db.models.fields.related import OneToOneRel, ManyToOneRel, OneToOneField
 from django.db.models.query import delete_objects, Q
 from django.db.models.options import Options, AdminOptions
 from django.db import connection, transaction
@@ -14,10 +19,6 @@ from django.utils.datastructures import SortedDict
 from django.utils.functional import curry
 from django.utils.encoding import smart_str, force_unicode, smart_unicode
 from django.conf import settings
-from itertools import izip
-import types
-import sys
-import os
 
 class ModelBase(type):
     "Metaclass for all models"
@@ -25,29 +26,46 @@ class ModelBase(type):
         # If this isn't a subclass of Model, don't do anything special.
         try:
             parents = [b for b in bases if issubclass(b, Model)]
-            if not parents:
-                return super(ModelBase, cls).__new__(cls, name, bases, attrs)
         except NameError:
             # 'Model' isn't defined yet, meaning we're looking at Django's own
             # Model class, defined below.
+            parents = []
+        if not parents:
             return super(ModelBase, cls).__new__(cls, name, bases, attrs)
 
         # Create the class.
         new_class = type.__new__(cls, name, bases, {'__module__': attrs.pop('__module__')})
-        new_class.add_to_class('_meta', Options(attrs.pop('Meta', None)))
+        meta = attrs.pop('Meta', None)
+        # FIXME: Promote Meta to a newstyle class before attaching it to the
+        # model.
+        ## if meta:
+        ##     new_class.Meta = meta
+        new_class.add_to_class('_meta', Options(meta))
+        # FIXME: Need to be smarter here. Exception is an old-style class in
+        # Python <= 2.4, new-style in Python 2.5+. This construction is only
+        # really correct for old-style classes.
         new_class.add_to_class('DoesNotExist', types.ClassType('DoesNotExist', (ObjectDoesNotExist,), {}))
-        new_class.add_to_class('MultipleObjectsReturned',
-            types.ClassType('MultipleObjectsReturned', (MultipleObjectsReturned, ), {}))
+        new_class.add_to_class('MultipleObjectsReturned', types.ClassType('MultipleObjectsReturned', (MultipleObjectsReturned, ), {}))
 
-        # Build complete list of parents
+        # Do the appropriate setup for any model parents.
+        abstract_parents = []
         for base in parents:
-            # Things without _meta aren't functional models, so they're
-            # uninteresting parents.
-            if hasattr(base, '_meta'):
-                new_class._meta.parents.append(base)
-                new_class._meta.parents.extend(base._meta.parents)
-
+            if not hasattr(base, '_meta'):
+                # Things without _meta aren't functional models, so they're
+                # uninteresting parents.
+                continue
+            if not base._meta.abstract:
+                attr_name = '%s_ptr' % base._meta.module_name
+                field = OneToOneField(base, name=attr_name, auto_created=True)
+                new_class.add_to_class(attr_name, field)
+                new_class._meta.parents[base] = field
+            else:
+                abstract_parents.append(base)
 
+        if getattr(new_class, '_default_manager', None) is not None:
+            # We have a parent who set the default manager. We need to override
+            # this.
+            new_class._default_manager = None
         if getattr(new_class._meta, 'app_label', None) is None:
             # Figure out the app_label by looking one level up.
             # For 'django.contrib.sites.models', this would be 'sites'.
@@ -63,21 +81,26 @@ class ModelBase(type):
         for obj_name, obj in attrs.items():
             new_class.add_to_class(obj_name, obj)
 
-        # Add Fields inherited from parents
-        for parent in new_class._meta.parents:
-            for field in parent._meta.fields:
-                # Only add parent fields if they aren't defined for this class.
-                try:
-                    new_class._meta.get_field(field.name)
-                except FieldDoesNotExist:
-                    field.contribute_to_class(new_class, field.name)
+        for parent in abstract_parents:
+            names = [f.name for f in new_class._meta.local_fields + new_class._meta.many_to_many]
+            for field in parent._meta.local_fields:
+                if field.name in names:
+                    raise TypeError('Local field %r in class %r clashes with field of similar name from abstract base class %r'
+                            % (field.name, name, parent.__name__))
+                new_class.add_to_class(field.name, field)
+
+        if new_class._meta.abstract:
+            # Abstract base models can't be instantiated and don't appear in
+            # the list of models for an app. We do the final setup for them a
+            # little differently from normal models.
+            return new_class
 
         new_class._prepare()
-
         register_models(new_class._meta.app_label, new_class)
+
         # Because of the way imports happen (recursively), we may or may not be
-        # the first class for this model to register with the framework. There
-        # should only be one class for each model, so we must always return the
+        # the first time this model tries to register with the framework. There
+        # should only be one class for each model, so we always return the
         # registered version.
         return get_model(new_class._meta.app_label, name, False)
 
@@ -113,8 +136,10 @@ class ModelBase(type):
 class Model(object):
     __metaclass__ = ModelBase
 
-    def _get_pk_val(self):
-        return getattr(self, self._meta.pk.attname)
+    def _get_pk_val(self, meta=None):
+        if not meta:
+            meta = self._meta
+        return getattr(self, meta.pk.attname)
 
     def _set_pk_val(self, value):
         return setattr(self, self._meta.pk.attname, value)
@@ -207,19 +232,30 @@ class Model(object):
                 raise TypeError, "'%s' is an invalid keyword argument for this function" % kwargs.keys()[0]
         dispatcher.send(signal=signals.post_init, sender=self.__class__, instance=self)
 
-    def save(self, raw=False):
-        dispatcher.send(signal=signals.pre_save, sender=self.__class__,
-                        instance=self, raw=raw)
+    def save(self, raw=False, cls=None):
+        if not cls:
+            dispatcher.send(signal=signals.pre_save, sender=self.__class__,
+                    instance=self, raw=raw)
+            cls = self.__class__
+            meta = self._meta
+            signal = True
+        else:
+            meta = cls._meta
+            signal = False
 
-        non_pks = [f for f in self._meta.fields if not f.primary_key]
+        for parent, field in meta.parents.items():
+            self.save(raw, parent)
+            setattr(self, field.attname, self._get_pk_val(parent._meta))
+
+        non_pks = [f for f in self._meta.local_fields if not f.primary_key]
 
         # First, try an UPDATE. If that doesn't update anything, do an INSERT.
-        pk_val = self._get_pk_val()
+        pk_val = self._get_pk_val(meta)
         # Note: the comparison with '' is required for compatibility with
         # oldforms-style model creation.
         pk_set = pk_val is not None and smart_unicode(pk_val) != u''
         record_exists = True
-        manager = self.__class__._default_manager
+        manager = cls._default_manager
         if pk_set:
             # Determine whether a record with the primary key already exists.
             if manager.filter(pk=pk_val).extra(select={'a': 1}).values('a').order_by():
@@ -231,16 +267,16 @@ class Model(object):
                 record_exists = False
         if not pk_set or not record_exists:
             if not pk_set:
-                values = [(f.name, f.get_db_prep_save(raw and getattr(self, f.attname) or f.pre_save(self, True))) for f in self._meta.fields if not isinstance(f, AutoField)]
+                values = [(f.name, f.get_db_prep_save(raw and getattr(self, f.attname) or f.pre_save(self, True))) for f in meta.local_fields if not isinstance(f, AutoField)]
             else:
-                values = [(f.name, f.get_db_prep_save(raw and getattr(self, f.attname) or f.pre_save(self, True))) for f in self._meta.fields]
+                values = [(f.name, f.get_db_prep_save(raw and getattr(self, f.attname) or f.pre_save(self, True))) for f in meta.local_fields]
 
-            if self._meta.order_with_respect_to:
-                field = self._meta.order_with_respect_to
+            if meta.order_with_respect_to:
+                field = meta.order_with_respect_to
                 values.append(('_order', manager.filter(**{field.name: getattr(self, field.attname)}).count()))
             record_exists = False
 
-            update_pk = bool(self._meta.has_auto_field and not pk_set)
+            update_pk = bool(meta.has_auto_field and not pk_set)
             if values:
                 # Create a new record.
                 result = manager._insert(_return_id=update_pk, **dict(values))
@@ -250,12 +286,13 @@ class Model(object):
                         _raw_values=True, pk=connection.ops.pk_default_value())
 
             if update_pk:
-                setattr(self, self._meta.pk.attname, result)
+                setattr(self, meta.pk.attname, result)
         transaction.commit_unless_managed()
 
-        # Run any post-save hooks.
-        dispatcher.send(signal=signals.post_save, sender=self.__class__,
-                        instance=self, created=(not record_exists), raw=raw)
+        if signal:
+            # Run any post-save hooks.
+            dispatcher.send(signal=signals.post_save, sender=self.__class__,
+                    instance=self, created=(not record_exists), raw=raw)
 
     save.alters_data = True
 
diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index a3d7d05e16..c2edc71573 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -75,15 +75,19 @@ class Field(object):
     # database level.
     empty_strings_allowed = True
 
-    # Tracks each time a Field instance is created. Used to retain order.
+    # These track each time a Field instance is created. Used to retain order.
+    # The auto_creation_counter is used for fields that Django implicitly
+    # creates, creation_counter is used for all user-specified fields.
     creation_counter = 0
+    auto_creation_counter = -1
 
     def __init__(self, verbose_name=None, name=None, primary_key=False,
-        max_length=None, unique=False, blank=False, null=False, db_index=False,
-        core=False, rel=None, default=NOT_PROVIDED, editable=True, serialize=True,
-        prepopulate_from=None, unique_for_date=None, unique_for_month=None,
-        unique_for_year=None, validator_list=None, choices=None, radio_admin=None,
-        help_text='', db_column=None, db_tablespace=None):
+            max_length=None, unique=False, blank=False, null=False,
+            db_index=False, core=False, rel=None, default=NOT_PROVIDED,
+            editable=True, serialize=True, prepopulate_from=None,
+            unique_for_date=None, unique_for_month=None, unique_for_year=None,
+            validator_list=None, choices=None, radio_admin=None, help_text='',
+            db_column=None, db_tablespace=None, auto_created=False):
         self.name = name
         self.verbose_name = verbose_name
         self.primary_key = primary_key
@@ -109,9 +113,13 @@ class Field(object):
         # Set db_index to True if the field has a relationship and doesn't explicitly set db_index.
         self.db_index = db_index
 
-        # Increase the creation counter, and save our local copy.
-        self.creation_counter = Field.creation_counter
-        Field.creation_counter += 1
+        # Adjust the appropriate creation counter, and save our local copy.
+        if auto_created:
+            self.creation_counter = Field.auto_creation_counter
+            Field.auto_creation_counter -= 1
+        else:
+            self.creation_counter = Field.creation_counter
+            Field.creation_counter += 1
 
     def __cmp__(self, other):
         # This is needed because bisect does not take a comparison function.
diff --git a/django/db/models/fields/related.py b/django/db/models/fields/related.py
index a7c4fca2fd..39fe6d794c 100644
--- a/django/db/models/fields/related.py
+++ b/django/db/models/fields/related.py
@@ -494,8 +494,9 @@ class OneToOneRel(ManyToOneRel):
         # ignored here. We accept them as parameters only to match the calling
         # signature of ManyToOneRel.__init__().
         super(OneToOneRel, self).__init__(to, field_name, num_in_admin,
-                edit_inline, related_name, limit_choices_to, lookup_overrides,
-                raw_id_admin)
+                edit_inline=edit_inline, related_name=related_name,
+                limit_choices_to=limit_choices_to,
+                lookup_overrides=lookup_overrides, raw_id_admin=raw_id_admin)
         self.multiple = False
 
 class ManyToManyRel(object):
@@ -754,7 +755,7 @@ class ManyToManyField(RelatedField, Field):
 
     def save_form_data(self, instance, data):
         setattr(instance, self.attname, data)
-        
+
     def formfield(self, **kwargs):
         defaults = {'form_class': forms.ModelMultipleChoiceField, 'queryset': self.rel.to._default_manager.all()}
         defaults.update(kwargs)
diff --git a/django/db/models/manager.py b/django/db/models/manager.py
index ed420e1333..34811cd324 100644
--- a/django/db/models/manager.py
+++ b/django/db/models/manager.py
@@ -5,7 +5,7 @@ from django.db.models.fields import FieldDoesNotExist
 
 def ensure_default_manager(sender):
     cls = sender
-    if not hasattr(cls, '_default_manager'):
+    if not hasattr(cls, '_default_manager') or cls._default_manager is None:
         # Create the default manager, if needed.
         try:
             cls._meta.get_field('objects')
@@ -31,7 +31,7 @@ class Manager(object):
         # TODO: Use weakref because of possible memory leak / circular reference.
         self.model = model
         setattr(model, name, ManagerDescriptor(self))
-        if not hasattr(model, '_default_manager') or self.creation_counter < model._default_manager.creation_counter:
+        if not hasattr(model, '_default_manager') or model._default_manager is None or self.creation_counter < model._default_manager.creation_counter:
             model._default_manager = self
 
     #######################
diff --git a/django/db/models/options.py b/django/db/models/options.py
index 8d80a0ac8d..8c369f98a6 100644
--- a/django/db/models/options.py
+++ b/django/db/models/options.py
@@ -1,3 +1,6 @@
+import re
+from bisect import bisect
+
 from django.conf import settings
 from django.db.models.related import RelatedObject
 from django.db.models.fields.related import ManyToManyRel
@@ -7,19 +10,19 @@ from django.db.models.loading import get_models, app_cache_ready
 from django.db.models import Manager
 from django.utils.translation import activate, deactivate_all, get_language, string_concat
 from django.utils.encoding import force_unicode, smart_str
-from bisect import bisect
-import re
+from django.utils.datastructures import SortedDict
 
 # Calculate the verbose_name by converting from InitialCaps to "lowercase with spaces".
 get_verbose_name = lambda class_name: re.sub('(((?<=[a-z])[A-Z])|([A-Z](?![A-Z]|$)))', ' \\1', class_name).lower().strip()
 
 DEFAULT_NAMES = ('verbose_name', 'db_table', 'ordering',
                  'unique_together', 'permissions', 'get_latest_by',
-                 'order_with_respect_to', 'app_label', 'db_tablespace')
+                 'order_with_respect_to', 'app_label', 'db_tablespace',
+                 'abstract')
 
 class Options(object):
     def __init__(self, meta):
-        self.fields, self.many_to_many = [], []
+        self.local_fields, self.local_many_to_many = [], []
         self.module_name, self.verbose_name = None, None
         self.verbose_name_plural = None
         self.db_table = ''
@@ -35,7 +38,8 @@ class Options(object):
         self.pk = None
         self.has_auto_field, self.auto_field = False, None
         self.one_to_one_field = None
-        self.parents = []
+        self.abstract = False
+        self.parents = SortedDict()
 
     def contribute_to_class(self, cls, name):
         cls._meta = self
@@ -82,9 +86,16 @@ class Options(object):
             self.order_with_respect_to = None
 
         if self.pk is None:
-            auto = AutoField(verbose_name='ID', primary_key=True)
-            auto.creation_counter = -1
-            model.add_to_class('id', auto)
+            if self.parents:
+                # Promote the first parent link in lieu of adding yet another
+                # field.
+                field = self.parents.value_for_index(0)
+                field.primary_key = True
+                self.pk = field
+            else:
+                auto = AutoField(verbose_name='ID', primary_key=True,
+                        auto_created=True)
+                model.add_to_class('id', auto)
 
         # If the db_table wasn't provided, use the app_label + module_name.
         if not self.db_table:
@@ -97,13 +108,23 @@ class Options(object):
         # Move many-to-many related fields from self.fields into
         # self.many_to_many.
         if field.rel and isinstance(field.rel, ManyToManyRel):
-            self.many_to_many.insert(bisect(self.many_to_many, field), field)
+            self.local_many_to_many.insert(bisect(self.local_many_to_many, field), field)
         else:
-            self.fields.insert(bisect(self.fields, field), field)
+            self.local_fields.insert(bisect(self.local_fields, field), field)
             if not self.pk and field.primary_key:
                 self.pk = field
                 field.serialize = False
 
+        # All of these internal caches need to be updated the next time they
+        # are used.
+        # TODO: Do this more neatly. (Also, use less caches!)
+        if hasattr(self, '_field_cache'):
+            del self._field_cache
+        if hasattr(self, '_m2m_cache'):
+            del self._m2m_cache
+        if hasattr(self, '_name_map'):
+            del self._name_map
+
     def __repr__(self):
         return '<Options for %s>' % self.object_name
 
@@ -123,8 +144,76 @@ class Options(object):
         return raw
     verbose_name_raw = property(verbose_name_raw)
 
+    def _fields(self):
+        """
+        The getter for self.fields. This returns the list of field objects
+        available to this model (including through parent models).
+        """
+        try:
+            self._field_cache
+        except AttributeError:
+            self._fill_fields_cache()
+        return self._field_cache.keys()
+    fields = property(_fields)
+
+    def get_fields_with_model(self):
+        """
+        Returns a list of (field, model) pairs for all fields. The "model"
+        element is None for fields on the current model. Mostly of use when
+        constructing queries so that we know which model a field belongs to.
+        """
+        try:
+            self._field_cache
+        except AttributeError:
+            self._fill_fields_cache()
+        return self._field_cache.items()
+
+    def _fill_fields_cache(self):
+        cache = SortedDict()
+        for parent in self.parents:
+            for field, model in parent._meta.get_fields_with_model():
+                if model:
+                    cache[field] = model
+                else:
+                    cache[field] = parent
+        for field in self.local_fields:
+            cache[field] = None
+        self._field_cache = cache
+
+    def _many_to_many(self):
+        try:
+            self._m2m_cache
+        except AttributeError:
+            self._fill_m2m_cache()
+        return self._m2m_cache.keys()
+    many_to_many = property(_many_to_many)
+
+    def get_m2m_with_model(self):
+        """
+        The many-to-many version of get_fields_with_model().
+        """
+        try:
+            self._m2m_cache
+        except AttributeError:
+            self._fill_m2m_cache()
+        return self._m2m_cache.items()
+
+    def _fill_m2m_cache(self):
+        cache = SortedDict()
+        for parent in self.parents:
+            for field, model in parent._meta.get_m2m_with_model():
+                if model:
+                    cache[field] = model
+                else:
+                    cache[field] = parent
+        for field in self.local_many_to_many:
+            cache[field] = None
+        self._m2m_cache = cache
+
     def get_field(self, name, many_to_many=True):
-        "Returns the requested field by name. Raises FieldDoesNotExist on error."
+        """
+        Returns the requested field by name. Raises FieldDoesNotExist on error.
+        """
         to_search = many_to_many and (self.fields + self.many_to_many) or self.fields
         for f in to_search:
             if f.name == name:
@@ -133,8 +222,9 @@ class Options(object):
 
     def get_field_by_name(self, name, only_direct=False):
         """
-        Returns the (field_object, direct, m2m), where field_object is the
-        Field instance for the given name, direct is True if the field exists
+        Returns the (field_object, model, direct, m2m), where field_object is
+        the Field instance for the given name, model is the model containing
+        this field (None for local fields), direct is True if the field exists
         on this model, and m2m is True for many-to-many relations. When
         'direct' is False, 'field_object' is the corresponding RelatedObject
         for this field (since the field doesn't have an instance associated
@@ -151,7 +241,7 @@ class Options(object):
             cache = self.init_name_map()
             result = cache.get(name)
 
-        if not result or (not result[1] and only_direct):
+        if not result or (only_direct and not result[2]):
             raise FieldDoesNotExist('%s has no field named %r'
                     % (self.object_name, name))
         return result
@@ -173,15 +263,16 @@ class Options(object):
         """
         Initialises the field name -> field object mapping.
         """
-        cache = dict([(f.name, (f, True, False)) for f in self.fields])
-        for f in self.many_to_many:
-            cache[f.name] = (f, True, True)
-        for f in self.get_all_related_many_to_many_objects():
-            cache[f.field.related_query_name()] = (f, False, True)
-        for f in self.get_all_related_objects():
-            cache[f.field.related_query_name()] = (f, False, False)
+        cache = dict([(f.name, (f, m, True, False)) for f, m in
+                self.get_fields_with_model()])
+        for f, model in self.get_m2m_with_model():
+            cache[f.name] = (f, model, True, True)
+        for f, model in self.get_all_related_m2m_objects_with_model():
+            cache[f.field.related_query_name()] = (f, model, False, True)
+        for f, model in self.get_all_related_objects_with_model():
+            cache[f.field.related_query_name()] = (f, model, False, False)
         if self.order_with_respect_to:
-            cache['_order'] = OrderWrt(), True, False
+            cache['_order'] = OrderWrt(), None, True, False
         if app_cache_ready():
             self._name_map = cache
         return cache
@@ -195,17 +286,81 @@ class Options(object):
     def get_delete_permission(self):
         return 'delete_%s' % self.object_name.lower()
 
-    def get_all_related_objects(self):
-        try: # Try the cache first.
-            return self._all_related_objects
+    def get_all_related_objects(self, local_only=False):
+        try:
+            self._related_objects_cache
         except AttributeError:
-            rel_objs = []
-            for klass in get_models():
-                for f in klass._meta.fields:
-                    if f.rel and not isinstance(f.rel.to, str) and self == f.rel.to._meta:
-                        rel_objs.append(RelatedObject(f.rel.to, klass, f))
-            self._all_related_objects = rel_objs
-            return rel_objs
+            self._fill_related_objects_cache()
+        if local_only:
+            return [k for k, v in self._related_objects_cache.items() if not v]
+        return self._related_objects_cache.keys()
+
+    def get_all_related_objects_with_model(self):
+        """
+        Returns a list of (related-object, model) pairs. Similar to
+        get_fields_with_model().
+        """
+        try:
+            self._related_objects_cache
+        except AttributeError:
+            self._fill_related_objects_cache()
+        return self._related_objects_cache.items()
+
+    def _fill_related_objects_cache(self):
+        cache = SortedDict()
+        parent_list = self.get_parent_list()
+        for parent in self.parents:
+            for obj, model in parent._meta.get_all_related_objects_with_model():
+                if obj.field.creation_counter < 0 and obj.model not in parent_list:
+                    continue
+                if not model:
+                    cache[obj] = parent
+                else:
+                    cache[obj] = model
+        for klass in get_models():
+            for f in klass._meta.local_fields:
+                if f.rel and not isinstance(f.rel.to, str) and self == f.rel.to._meta:
+                    cache[RelatedObject(f.rel.to, klass, f)] = None
+        self._related_objects_cache = cache
+
+    def get_all_related_many_to_many_objects(self, local_only=False):
+        try:
+            cache = self._related_many_to_many_cache
+        except AttributeError:
+            cache = self._fill_related_many_to_many_cache()
+        if local_only:
+            return [k for k, v in cache.items() if not v]
+        return cache.keys()
+
+    def get_all_related_m2m_objects_with_model(self):
+        """
+        Returns a list of (related-m2m-object, model) pairs. Similar to
+        get_fields_with_model().
+        """
+        try:
+            cache = self._related_many_to_many_cache
+        except AttributeError:
+            cache = self._fill_related_many_to_many_cache()
+        return cache.items()
+
+    def _fill_related_many_to_many_cache(self):
+        cache = SortedDict()
+        parent_list = self.get_parent_list()
+        for parent in self.parents:
+            for obj, model in parent._meta.get_all_related_m2m_objects_with_model():
+                if obj.field.creation_counter < 0 and obj.model not in parent_list:
+                    continue
+                if not model:
+                    cache[obj] = parent
+                else:
+                    cache[obj] = model
+        for klass in get_models():
+            for f in klass._meta.local_many_to_many:
+                if f.rel and not isinstance(f.rel.to, str) and self == f.rel.to._meta:
+                    cache[RelatedObject(f.rel.to, klass, f)] = None
+        if app_cache_ready():
+            self._related_many_to_many_cache = cache
+        return cache
 
     def get_followed_related_objects(self, follow=None):
         if follow == None:
@@ -229,18 +384,35 @@ class Options(object):
                 follow[f.name] = fol
         return follow
 
-    def get_all_related_many_to_many_objects(self):
-        try: # Try the cache first.
-            return self._all_related_many_to_many_objects
-        except AttributeError:
-            rel_objs = []
-            for klass in get_models():
-                for f in klass._meta.many_to_many:
-                    if f.rel and not isinstance(f.rel.to, str) and self == f.rel.to._meta:
-                        rel_objs.append(RelatedObject(f.rel.to, klass, f))
-            if app_cache_ready():
-                self._all_related_many_to_many_objects = rel_objs
-            return rel_objs
+    def get_base_chain(self, model):
+        """
+        Returns a list of parent classes leading to 'model' (order from closet
+        to most distant ancestor). This has to handle the case were 'model' is
+        a granparent or even more distant relation.
+        """
+        if not self.parents:
+            return
+        if model in self.parents:
+            return [model]
+        for parent in self.parents:
+            res = parent._meta.get_base_chain(model)
+            if res:
+                res.insert(0, parent)
+                return res
+        raise TypeError('%r is not an ancestor of this model'
+                % model._meta.module_name)
+
+    def get_parent_list(self):
+        """
+        Returns a list of all the ancestor of this model as a list. Useful for
+        determining if something is an ancestor, regardless of lineage.
+        """
+        # FIXME: Fix model hashing and then use a Set here.
+        result = []
+        for parent in self.parents:
+            result.append(parent)
+            result.extend(parent._meta.get_parent_list())
+        return result
 
     def get_ordered_objects(self):
         "Returns a list of Options objects that are ordered with respect to this object."
diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index 7d95e1d603..7b70e4d1b2 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -389,8 +389,13 @@ class Query(object):
                         aliases.append(col.alias)
         elif self.default_cols:
             table_alias = self.tables[0]
-            result = ['%s.%s' % (qn(table_alias), qn(f.column))
-                    for f in self.model._meta.fields]
+            root_pk = self.model._meta.pk.column
+            seen = {None: table_alias}
+            for field, model in self.model._meta.get_fields_with_model():
+                if model not in seen:
+                    seen[model] = self.join((table_alias, model._meta.db_table,
+                            root_pk, model._meta.pk.column))
+                result.append('%s.%s' % (qn(seen[model]), qn(field.column)))
             aliases = result[:]
 
         result.extend(['(%s) AS %s' % (col, alias)
@@ -742,7 +747,7 @@ class Query(object):
         opts = self.model._meta
         alias = self.join((None, opts.db_table, None, None))
 
-        field, target, unused, join_list, = self.setup_joins(parts, opts,
+        field, target, opts, join_list, = self.setup_joins(parts, opts,
                 alias, (connector == AND))
         col = target.column
         alias = join_list[-1][-1]
@@ -850,11 +855,21 @@ class Query(object):
                 name = opts.pk.name
 
             try:
-                field, direct, m2m = opts.get_field_by_name(name)
+                field, model, direct, m2m = opts.get_field_by_name(name)
             except FieldDoesNotExist:
                 names = opts.get_all_field_names()
                 raise TypeError("Cannot resolve keyword %r into field. "
                         "Choices are: %s" % (name, ", ".join(names)))
+            if model:
+                # The field lives on a base class of the current model.
+                alias_list = []
+                for int_model in opts.get_base_chain(model):
+                    lhs_col = opts.parents[int_model].column
+                    opts = int_model._meta
+                    alias = self.join((alias, opts.db_table, lhs_col,
+                            opts.pk.column))
+                    alias_list.append(alias)
+                joins.append(alias_list)
             cached_data = opts._join_cache.get(name)
             orig_opts = opts
 
@@ -899,6 +914,7 @@ class Query(object):
                             nullable=field.null)
                     joins.append([alias])
                 else:
+                    # Non-relation fields.
                     target = field
                     break
             else:
@@ -1242,7 +1258,7 @@ class UpdateQuery(Query):
     def add_update_values(self, values):
         from django.db.models.base import Model
         for name, val in values.items():
-            field, direct, m2m = self.model._meta.get_field_by_name(name)
+            field, model, direct, m2m = self.model._meta.get_field_by_name(name)
             if not direct or m2m:
                 # Can only update non-relation fields and foreign keys.
                 raise TypeError('Cannot update model field %r (only non-relations and foreign keys permitted).' % field)
diff --git a/docs/model-api.txt b/docs/model-api.txt
index cccd2ffded..6ca08ae4e5 100644
--- a/docs/model-api.txt
+++ b/docs/model-api.txt
@@ -2028,6 +2028,105 @@ You can also prevent saving::
 
 .. _database API docs: ../db-api/
 
+Model inheritance
+=================
+
+Abstract base classes
+---------------------
+
+Abstract base classes are useful when you want to put some common information
+into a number of other models. You write your base class and put
+``abstract=True`` in the ``Meta`` class. This model will then not be used to
+create any database table. Instead, when it is used as a base class for other
+models, its fields will be added to those of the child class. It is an error
+to have fields in the abstract base class with the same name as those in the
+child (and Django will raise an exception).
+
+An example::
+
+    class CommonInfo(models.Model):
+        name = models.CharField(max_length=100)
+        age = models.PositiveIntegerField()
+
+        class Meta:
+            abstract = True
+
+    class Student(CommonInfo):
+        home_group = models.CharField(max_length=5)
+
+The ``Student`` model will have three fields: ``name``, ``age`` and
+``home_group``. The ``CommonInfo`` model cannot be used as a normal Django
+model, since it is an abstract base class. It does not generate a database
+table or have a manager or anything like that.
+
+For many uses, this type of model inheritance will be exactly what you want.
+It provides a way to factor out common information at the Python level, whilst
+still only creating one database table per child model at the database level.
+
+Multi-table inheritance
+-----------------------
+
+The second type of model inheritance supported by Django is when each model in
+the hierarchy is a model all by itself. Each model corresponds to its own
+database table and can be queried and created indvidually. The inheritance
+relationship introduces links between the child model and each of its parents
+(via an automatically created ``OneToOneField``). For example::
+
+    class Place(models.Model):
+        name = models.CharField(max_length=50)
+        address = models.CharField(max_length=80)
+
+    class Restaurant(Place):
+        serves_hot_dogs = models.BooleanField()
+        serves_pizza = models.BooleanField()
+
+All of the fields of ``Place`` will also be available in ``Restaurant``,
+although the data will reside in a different database table. So these are both
+possible::
+
+    >>> Place.objects.filter(name="Bob's Cafe")
+    >>> Restaurant.objects.filter(name="Bob's Cafe")
+
+If you have a ``Place`` that is also a ``Restaurant``, you can get from the
+``Place`` object to the ``Restaurant`` object by using the lower-case version
+of the model name::
+
+    >>> p = Place.objects.filter(name="Bob's Cafe")
+    # If Bob's Cafe is a Restaurant object, this will give the child class:
+    >>> p.restaurant
+    <Restaurant: ...>
+
+However, if ``p`` in the above example was *not* a ``Restaurant`` (it had been
+created directly as a ``Place`` object or was the parent of some other class),
+referring to ``p.restaurant`` would give an error.
+
+Normally you won't need to worry too much about how model inheritance works.
+It will behave similarly to Python class inheritance.
+
+Inheritance and reverse relations
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Because multi-table inheritance uses an implicit ``OneToOneField`` to link the
+child and the parent, it's possible to move from the parent down to the child,
+as in the above example. However, this uses up the name that is the default
+``related_name`` value for ``ForeignKey`` and ``ManyToManyField`` relations.
+If you are putting those type of relations on a subclass of another model, you
+**must** specify the ``related_name`` attribute on each such field. If you
+forget, Django will raise an error when you run ``manage.py validate`` or try
+to syncdb.
+
+For example, using the above ``Place`` class again, let's create another
+subclass with a ``ManyToManyField``::
+
+    class Supplier(Place):
+        # Must specify related_name on all relations.
+        customers = models.ManyToManyField(Restaurant,
+                related_name='provider')
+
+For more information about reverse relations, refer to the `Database API
+reference`_ . For now, just remember to run ``manage.py validate`` when
+you're writing your models and pay attention to the error messages.
+
 Models across files
 ===================
 
diff --git a/tests/modeltests/model_inheritance/models.py b/tests/modeltests/model_inheritance/models.py
index d9956a5452..940b2ee10c 100644
--- a/tests/modeltests/model_inheritance/models.py
+++ b/tests/modeltests/model_inheritance/models.py
@@ -1,11 +1,35 @@
 """
 XX. Model inheritance
 
-Model inheritance isn't yet supported.
+Model inheritance exists in two varieties:
+    - abstract base classes which are a way of specifying common
+      information inherited by the subclasses. They don't exist as a separate
+      model.
+    - non-abstract base classes (the default), which are models in their own
+      right with their own database tables and everything. Their subclasses
+      have references back to them, created automatically.
+
+Both styles are demonstrated here.
 """
 
 from django.db import models
 
+class CommonInfo(models.Model):
+    name = models.CharField(max_length=50)
+    age = models.PositiveIntegerField()
+
+    class Meta:
+        abstract = True
+
+    def __unicode__(self):
+        return u'%s %s' % (self.__class__.__name__, self.name)
+
+class Worker(CommonInfo):
+    job = models.CharField(max_length=50)
+
+class Student(CommonInfo):
+    school_class = models.CharField(max_length=10)
+
 class Place(models.Model):
     name = models.CharField(max_length=50)
     address = models.CharField(max_length=80)
@@ -26,16 +50,44 @@ class ItalianRestaurant(Restaurant):
     def __unicode__(self):
         return u"%s the italian restaurant" % self.name
 
-# XFAIL: Recent changes to model saving mean these now fail catastrophically.
-# They'll be re-enabled when the porting is a bit further along.
-not__test__ = {'API_TESTS':"""
-# Make sure Restaurant has the right fields in the right order.
->>> [f.name for f in Restaurant._meta.fields]
-['id', 'name', 'address', 'serves_hot_dogs', 'serves_pizza']
+class Supplier(Place):
+    customers = models.ManyToManyField(Restaurant, related_name='provider')
 
-# Make sure ItalianRestaurant has the right fields in the right order.
->>> [f.name for f in ItalianRestaurant._meta.fields]
-['id', 'name', 'address', 'serves_hot_dogs', 'serves_pizza', 'serves_gnocchi']
+    def __unicode__(self):
+        return u"%s the supplier" % self.name
+
+class ParkingLot(Place):
+    main_site = models.ForeignKey(Place, related_name='lot')
+
+    def __unicode__(self):
+        return u"%s the parking lot" % self.name
+
+__test__ = {'API_TESTS':"""
+# The Student and Worker models both have 'name' and 'age' fields on them and
+# inherit the __unicode__() method, just as with normal Python subclassing.
+# This is useful if you want to factor out common information for programming
+# purposes, but still completely independent separate models at the database
+# level.
+
+>>> w = Worker(name='Fred', age=35, job='Quarry worker')
+>>> w.save()
+>>> s = Student(name='Pebbles', age=5, school_class='1B')
+>>> s.save()
+>>> unicode(w)
+u'Worker Fred'
+>>> unicode(s)
+u'Student Pebbles'
+
+# However, the CommonInfo class cannot be used as a normal model (it doesn't
+# exist as a model).
+>>> CommonInfo.objects.all()
+Traceback (most recent call last):
+    ...
+AttributeError: type object 'CommonInfo' has no attribute 'objects'
+
+# The Place/Restaurant/ItalianRestaurant models, on the other hand, all exist
+# as independent models. However, the subclasses also have transparent access
+# to the fields of their ancestors.
 
 # Create a couple of Places.
 >>> p1 = Place(name='Master Shakes', address='666 W. Jersey')
@@ -43,7 +95,7 @@ not__test__ = {'API_TESTS':"""
 >>> p2 = Place(name='Ace Hardware', address='1013 N. Ashland')
 >>> p2.save()
 
-# Test constructor for Restaurant.
+Test constructor for Restaurant.
 >>> r = Restaurant(name='Demon Dogs', address='944 W. Fullerton', serves_hot_dogs=True, serves_pizza=False)
 >>> r.save()
 
@@ -51,5 +103,88 @@ not__test__ = {'API_TESTS':"""
 >>> ir = ItalianRestaurant(name='Ristorante Miron', address='1234 W. Elm', serves_hot_dogs=False, serves_pizza=False, serves_gnocchi=True)
 >>> ir.save()
 
+# Make sure Restaurant and ItalianRestaurant have the right fields in the right
+# order.
+>>> [f.name for f in Restaurant._meta.fields]
+['id', 'name', 'address', 'place_ptr', 'serves_hot_dogs', 'serves_pizza']
+>>> [f.name for f in ItalianRestaurant._meta.fields]
+['id', 'name', 'address', 'place_ptr', 'serves_hot_dogs', 'serves_pizza', 'restaurant_ptr', 'serves_gnocchi']
+
+# Even though p.supplier for a Place 'p' (a parent of a Supplier), a Restaurant
+# object cannot access that reverse relation, since it's not part of the
+# Place-Supplier Hierarchy.
+>>> Place.objects.filter(supplier__name='foo')
+[]
+>>> Restaurant.objects.filter(supplier__name='foo')
+Traceback (most recent call last):
+    ...
+TypeError: Cannot resolve keyword 'supplier' into field. Choices are: address, id, italianrestaurant, lot, name, place_ptr, provider, serves_hot_dogs, serves_pizza
+
+# Parent fields can be used directly in filters on the child model.
+>>> Restaurant.objects.filter(name='Demon Dogs')
+[<Restaurant: Demon Dogs the restaurant>]
+>>> ItalianRestaurant.objects.filter(address='1234 W. Elm')
+[<ItalianRestaurant: Ristorante Miron the italian restaurant>]
+
+# Filters against the parent model return objects of the parent's type.
+>>> Place.objects.filter(name='Demon Dogs')
+[<Place: Demon Dogs the place>]
+
+# Since the parent and child are linked by an automatically created
+# OneToOneField, you can get from the parent to the child by using the child's
+# name.
+>>> place = Place.objects.get(name='Demon Dogs')
+>>> place.restaurant
+<Restaurant: Demon Dogs the restaurant>
+
+>>> Place.objects.get(name='Ristorante Miron').restaurant.italianrestaurant
+<ItalianRestaurant: Ristorante Miron the italian restaurant>
+>>> Restaurant.objects.get(name='Ristorante Miron').italianrestaurant
+<ItalianRestaurant: Ristorante Miron the italian restaurant>
+
+# This won't work because the Demon Dogs restaurant is not an Italian
+# restaurant.
+>>> place.restaurant.italianrestaurant
+Traceback (most recent call last):
+    ...
+DoesNotExist: ItalianRestaurant matching query does not exist.
+
+# Related objects work just as they normally do.
+
+>>> s1 = Supplier(name="Joe's Chickens", address='123 Sesame St')
+>>> s1.save()
+>>> s1.customers = [r, ir]
+>>> s2 = Supplier(name="Luigi's Pasta", address='456 Sesame St')
+>>> s2.save()
+>>> s2.customers = [ir]
+
+# This won't work because the Place we select is not a Restaurant (it's a
+# Supplier).
+>>> p = Place.objects.get(name="Joe's Chickens")
+>>> p.restaurant
+Traceback (most recent call last):
+    ...
+DoesNotExist: Restaurant matching query does not exist.
+
+# But we can descend from p to the Supplier child, as expected.
+>>> p.supplier
+<Supplier: Joe's Chickens the supplier>
+
+>>> ir.provider.order_by('-name')
+[<Supplier: Luigi's Pasta the supplier>, <Supplier: Joe's Chickens the supplier>]
+
+>>> Restaurant.objects.filter(provider__name__contains="Chickens")
+[<Restaurant: Demon Dogs the restaurant>, <Restaurant: Ristorante Miron the restaurant>]
+>>> ItalianRestaurant.objects.filter(provider__name__contains="Chickens")
+[<ItalianRestaurant: Ristorante Miron the italian restaurant>]
+
+>>> park1 = ParkingLot(name='Main St', address='111 Main St', main_site=s1)
+>>> park1.save()
+>>> park2 = ParkingLot(name='Well Lit', address='124 Sesame St', main_site=ir)
+>>> park2.save()
+
+>>> Restaurant.objects.get(lot__name='Well Lit')
+<Restaurant: Ristorante Miron the restaurant>
+
 
 """}