Split out a BaseAppCache, make AppCache borg again, add _meta.app_cache

Author: andrewgodwin

django/db/backends/sqlite3/schema.py

@@ -1,6 +1,6 @@
 from django.db.backends.schema import BaseDatabaseSchemaEditor
-from django.db.models.loading import cache, default_cache, AppCache
 from django.db.models.fields.related import ManyToManyField
+from django.db.models.loading import BaseAppCache
 
 
 class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
@@ -38,20 +38,19 @@ def _remake_table(self, model, create_fields=[], delete_fields=[], alter_fields=
         for field in delete_fields:
             del body[field.name]
             del mapping[field.column]
+        # Work inside a new AppCache
+        app_cache = BaseAppCache()
         # Construct a new model for the new state
         meta_contents = {
             'app_label': model._meta.app_label,
             'db_table': model._meta.db_table + "__new",
             'unique_together': model._meta.unique_together if override_uniques is None else override_uniques,
+            'app_cache': app_cache,
         }
         meta = type("Meta", tuple(), meta_contents)
         body['Meta'] = meta
         body['__module__'] = model.__module__
-        self.app_cache = AppCache()
-        cache.set_cache(self.app_cache)
-        cache.copy_from(default_cache)
         temp_model = type(model._meta.object_name, model.__bases__, body)
-        cache.set_cache(default_cache)
         # Create a new table with that format
         self.create_model(temp_model)
         # Copy data from the old table
@@ -117,9 +116,9 @@ def alter_field(self, model, old_field, new_field, strict=False):
             return self._alter_many_to_many(model, old_field, new_field, strict)
         elif old_type is None or new_type is None:
             raise ValueError("Cannot alter field %s into %s - they are not compatible types (probably means only one is an M2M with implicit through model)" % (
-                    old_field,
-                    new_field,
-                ))
+                old_field,
+                new_field,
+            ))
         # Alter by remaking table
         self._remake_table(model, alter_fields=[(old_field, new_field)])
 

django/db/models/base.py

@@ -19,7 +19,6 @@
 from django.db.models.deletion import Collector
 from django.db.models.options import Options
 from django.db.models import signals
-from django.db.models.loading import register_models, get_model
 from django.utils.translation import ugettext_lazy as _
 from django.utils.functional import curry
 from django.utils.encoding import force_str, force_text
@@ -134,7 +133,7 @@ def __new__(cls, name, bases, attrs):
                 new_class._base_manager = new_class._base_manager._copy_to_model(new_class)
 
         # Bail out early if we have already created this class.
-        m = get_model(new_class._meta.app_label, name,
+        m = new_class._meta.app_cache.get_model(new_class._meta.app_label, name,
                       seed_cache=False, only_installed=False)
         if m is not None:
             return m
@@ -242,16 +241,13 @@ def __new__(cls, name, bases, attrs):
 
         new_class._prepare()
 
-        if new_class._meta.auto_register:
-            register_models(new_class._meta.app_label, new_class)
-            # Because of the way imports happen (recursively), we may or may not be
-            # 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,
-                             seed_cache=False, only_installed=False)
-        else:
-            return new_class
+        new_class._meta.app_cache.register_models(new_class._meta.app_label, new_class)
+        # Because of the way imports happen (recursively), we may or may not be
+        # 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 new_class._meta.app_cache.get_model(new_class._meta.app_label, name,
+                         seed_cache=False, only_installed=False)
 
     def copy_managers(cls, base_managers):
         # This is in-place sorting of an Options attribute, but that's fine.

django/db/models/loading.py

@@ -16,57 +16,52 @@
         'load_app', 'app_cache_ready')
 
 
-class AppCache(object):
+def _initialize():
     """
-    A cache that stores installed applications and their models. Used to
-    provide reverse-relations and for app introspection (e.g. admin).
+    Returns a dictionary to be used as the initial value of the
+    [shared] state of the app cache.
     """
-
-    def __init__(self):
+    return dict(
         # Keys of app_store are the model modules for each application.
-        self.app_store = SortedDict()
+        app_store = SortedDict(),
+
         # Mapping of installed app_labels to model modules for that app.
-        self.app_labels = {}
+        app_labels = {},
+
         # Mapping of app_labels to a dictionary of model names to model code.
         # May contain apps that are not installed.
-        self.app_models = SortedDict()
+        app_models = SortedDict(),
+
         # Mapping of app_labels to errors raised when trying to import the app.
-        self.app_errors = {}
+        app_errors = {},
+
         # -- Everything below here is only used when populating the cache --
-        self.loaded = False
-        self.handled = {}
-        self.postponed = []
-        self.nesting_level = 0
-        self._get_models_cache = {}
+        loaded = False,
+        handled = {},
+        postponed = [],
+        nesting_level = 0,
+        _get_models_cache = {},
+    )
+
+
+class BaseAppCache(object):
+    """
+    A cache that stores installed applications and their models. Used to
+    provide reverse-relations and for app introspection (e.g. admin).
+
+    This provides the base (non-Borg) AppCache class - the AppCache
+    subclass adds borg-like behaviour for the few cases where it's needed,
+    and adds the code that auto-loads from INSTALLED_APPS.
+    """
+
+    def __init__(self):
+        self.__dict__ = _initialize()
 
     def _populate(self):
         """
-        Fill in all the cache information. This method is threadsafe, in the
-        sense that every caller will see the same state upon return, and if the
-        cache is already initialised, it does no work.
+        Stub method - this base class does no auto-loading.
         """
-        if self.loaded:
-            return
-        # Note that we want to use the import lock here - the app loading is
-        # in many cases initiated implicitly by importing, and thus it is
-        # possible to end up in deadlock when one thread initiates loading
-        # without holding the importer lock and another thread then tries to
-        # import something which also launches the app loading. For details of
-        # this situation see #18251.
-        imp.acquire_lock()
-        try:
-            if self.loaded:
-                return
-            for app_name in settings.INSTALLED_APPS:
-                if app_name in self.handled:
-                    continue
-                self.load_app(app_name, True)
-            if not self.nesting_level:
-                for app_name in self.postponed:
-                    self.load_app(app_name)
-                self.loaded = True
-        finally:
-            imp.release_lock()
+        self.loaded = True
 
     def _label_for(self, app_mod):
         """
@@ -253,42 +248,58 @@ def copy_from(self, other):
             self.register_models(app_label, *models.values())
 
 
-class AppCacheWrapper(object):
-    """
-    As AppCache can be changed at runtime, this class wraps it so any
-    imported references to 'cache' are changed along with it.
+class AppCache(BaseAppCache):
     """
+    A cache that stores installed applications and their models. Used to
+    provide reverse-relations and for app introspection (e.g. admin).
 
-    def __init__(self, cache):
-        self._cache = cache
+    Borg version of the BaseAppCache class.
+    """
 
-    def set_cache(self, cache):
-        self._cache = cache
+    __shared_state = _initialize()
 
-    def __getattr__(self, attr):
-        if attr in ("_cache", "set_cache"):
-            return self.__dict__[attr]
-        return getattr(self._cache, attr)
+    def __init__(self):
+        self.__dict__ = self.__shared_state
 
-    def __setattr__(self, attr, value):
-        if attr in ("_cache", "set_cache"):
-            self.__dict__[attr] = value
+    def _populate(self):
+        """
+        Fill in all the cache information. This method is threadsafe, in the
+        sense that every caller will see the same state upon return, and if the
+        cache is already initialised, it does no work.
+        """
+        if self.loaded:
             return
-        return setattr(self._cache, attr, value)
-
+        # Note that we want to use the import lock here - the app loading is
+        # in many cases initiated implicitly by importing, and thus it is
+        # possible to end up in deadlock when one thread initiates loading
+        # without holding the importer lock and another thread then tries to
+        # import something which also launches the app loading. For details of
+        # this situation see #18251.
+        imp.acquire_lock()
+        try:
+            if self.loaded:
+                return
+            for app_name in settings.INSTALLED_APPS:
+                if app_name in self.handled:
+                    continue
+                self.load_app(app_name, True)
+            if not self.nesting_level:
+                for app_name in self.postponed:
+                    self.load_app(app_name)
+                self.loaded = True
+        finally:
+            imp.release_lock()
 
-default_cache = AppCache()
-cache = AppCacheWrapper(default_cache)
+cache = AppCache()
 
 
 # These methods were always module level, so are kept that way for backwards
-# compatibility. These are wrapped with lambdas to stop the attribute
-# access resolving directly to a method on a single cache instance.
-get_apps = lambda *x, **y: cache.get_apps(*x, **y)
-get_app = lambda *x, **y: cache.get_app(*x, **y)
-get_app_errors = lambda *x, **y: cache.get_app_errors(*x, **y)
-get_models = lambda *x, **y: cache.get_models(*x, **y)
-get_model = lambda *x, **y: cache.get_model(*x, **y)
-register_models = lambda *x, **y: cache.register_models(*x, **y)
-load_app = lambda *x, **y: cache.load_app(*x, **y)
-app_cache_ready = lambda *x, **y: cache.app_cache_ready(*x, **y)
+# compatibility.
+get_apps = cache.get_apps
+get_app = cache.get_app
+get_app_errors = cache.get_app_errors
+get_models = cache.get_models
+get_model = cache.get_model
+register_models = cache.register_models
+load_app = cache.load_app
+app_cache_ready = cache.app_cache_ready

django/db/models/options.py

@@ -8,7 +8,7 @@
 from django.db.models.fields.related import ManyToManyRel
 from django.db.models.fields import AutoField, FieldDoesNotExist
 from django.db.models.fields.proxy import OrderWrt
-from django.db.models.loading import get_models, app_cache_ready
+from django.db.models.loading import get_models, app_cache_ready, cache
 from django.utils import six
 from django.utils.functional import cached_property
 from django.utils.datastructures import SortedDict
@@ -21,7 +21,7 @@
 DEFAULT_NAMES = ('verbose_name', 'verbose_name_plural', 'db_table', 'ordering',
                  'unique_together', 'permissions', 'get_latest_by',
                  'order_with_respect_to', 'app_label', 'db_tablespace',
-                 'abstract', 'managed', 'proxy', 'swappable', 'auto_created', 'index_together', 'auto_register')
+                 'abstract', 'managed', 'proxy', 'swappable', 'auto_created', 'index_together', 'app_cache')
 
 
 @python_2_unicode_compatible
@@ -70,8 +70,8 @@ def __init__(self, meta, app_label=None):
         # from *other* models. Needed for some admin checks. Internal use only.
         self.related_fkey_lookups = []
 
-        # If we should auto-register with the AppCache
-        self.auto_register = True
+        # A custom AppCache to use, if you're making a separate model set.
+        self.app_cache = cache
 
     def contribute_to_class(self, cls, name):
         from django.db import connection

tests/schema/models.py

@@ -1,33 +1,36 @@
 from django.db import models
+from django.db.models.loading import BaseAppCache
 
 # Because we want to test creation and deletion of these as separate things,
-# these models are all marked as unmanaged and only marked as managed while
-# a schema test is running.
+# these models are all inserted into a separate AppCache so the main test
+# runner doesn't syncdb them.
+
+new_app_cache = BaseAppCache()
 
 
 class Author(models.Model):
     name = models.CharField(max_length=255)
     height = models.PositiveIntegerField(null=True, blank=True)
 
     class Meta:
-        auto_register = False
+        app_cache = new_app_cache
 
 
 class AuthorWithM2M(models.Model):
     name = models.CharField(max_length=255)
 
     class Meta:
-        auto_register = False
+        app_cache = new_app_cache
 
 
 class Book(models.Model):
     author = models.ForeignKey(Author)
     title = models.CharField(max_length=100, db_index=True)
     pub_date = models.DateTimeField()
-    #tags = models.ManyToManyField("Tag", related_name="books")
+    # tags = models.ManyToManyField("Tag", related_name="books")
 
     class Meta:
-        auto_register = False
+        app_cache = new_app_cache
 
 
 class BookWithM2M(models.Model):
@@ -37,7 +40,7 @@ class BookWithM2M(models.Model):
     tags = models.ManyToManyField("Tag", related_name="books")
 
     class Meta:
-        auto_register = False
+        app_cache = new_app_cache
 
 
 class BookWithSlug(models.Model):
@@ -47,7 +50,7 @@ class BookWithSlug(models.Model):
     slug = models.CharField(max_length=20, unique=True)
 
     class Meta:
-        auto_register = False
+        app_cache = new_app_cache
         db_table = "schema_book"
 
 
@@ -56,15 +59,15 @@ class Tag(models.Model):
     slug = models.SlugField(unique=True)
 
     class Meta:
-        auto_register = False
+        app_cache = new_app_cache
 
 
 class TagUniqueRename(models.Model):
     title = models.CharField(max_length=255)
     slug2 = models.SlugField(unique=True)
 
     class Meta:
-        auto_register = False
+        app_cache = new_app_cache
         db_table = "schema_tag"
 
 
@@ -73,5 +76,5 @@ class UniqueTest(models.Model):
     slug = models.SlugField(unique=False)
 
     class Meta:
-        auto_register = False
+        app_cache = new_app_cache
         unique_together = ["year", "slug"]