"Utilities for loading models and the modules that contain them."
from django.conf import settings
from django.core.exceptions import ImproperlyConfigured
from django.utils.datastructures import SortedDict
from django.utils.importlib import import_module
from django.utils.module_loading import module_has_submodule
import imp
import sys
import os
import threading
__all__ = ('get_apps', 'get_app', 'get_models', 'get_model', 'register_models',
'load_app', 'app_cache_ready')
class AppCache(object):
"""
A cache that stores installed applications and their models. Used to
provide reverse-relations and for app introspection (e.g. admin).
"""
# Use the Borg pattern to share state between all instances. Details at
# http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/66531.
__shared_state = dict(
# Keys of app_store are the model modules for each application.
app_store = SortedDict(),
# Mapping of app_labels to a dictionary of model names to model code.
app_models = SortedDict(),
# Mapping of app_labels to errors raised when trying to import the app.
app_errors = {},
# -- Everything below here is only used when populating the cache --
loaded = False,
handled = {},
postponed = [],
nesting_level = 0,
write_lock = threading.RLock(),
_get_models_cache = {},
)
def __init__(self):
self.__dict__ = self.__shared_state
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
self.write_lock.acquire()
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:
self.write_lock.release()
def load_app(self, app_name, can_postpone=False):
"""
Loads the app with the provided fully qualified name, and returns the
model module.
"""
self.handled[app_name] = None
self.nesting_level += 1
app_module = import_module(app_name)
try:
models = import_module('.models', app_name)
except ImportError:
self.nesting_level -= 1
# If the app doesn't have a models module, we can just ignore the
# ImportError and return no models for it.
if not module_has_submodule(app_module, 'models'):
return None
# But if the app does have a models module, we need to figure out
# whether to suppress or propagate the error. If can_postpone is
# True then it may be that the package is still being imported by
# Python and the models module isn't available yet. So we add the
# app to the postponed list and we'll try it again after all the
# recursion has finished (in populate). If can_postpone is False
# then it's time to raise the ImportError.
else:
if can_postpone:
self.postponed.append(app_name)
return None
else:
raise
self.nesting_level -= 1
if models not in self.app_store:
self.app_store[models] = len(self.app_store)
return models
def app_cache_ready(self):
"""
Returns true if the model cache is fully populated.
Useful for code that wants to cache the results of get_models() for
themselves once it is safe to do so.
"""
return self.loaded
def get_apps(self):
"Returns a list of all installed modules that contain models."
self._populate()
# Ensure the returned list is always in the same order (with new apps
# added at the end). This avoids unstable ordering on the admin app
# list page, for example.
apps = [(v, k) for k, v in self.app_store.items()]
apps.sort()
return [elt[1] for elt in apps]
def get_app(self, app_label, emptyOK=False):
"""
Returns the module containing the models for the given app_label. If
the app has no models in it and 'emptyOK' is True, returns None.
"""
self._populate()
self.write_lock.acquire()
try:
for app_name in settings.INSTALLED_APPS:
if app_label == app_name.split('.')[-1]:
mod = self.load_app(app_name, False)
if mod is None:
if emptyOK:
return None
else:
return mod
raise ImproperlyConfigured("App with label %s could not be found" % app_label)
finally:
self.write_lock.release()
def get_app_errors(self):
"Returns the map of known problems with the INSTALLED_APPS."
self._populate()
return self.app_errors
def get_models(self, app_mod=None, include_auto_created=False, include_deferred=False):
"""
Given a module containing models, returns a list of the models.
Otherwise returns a list of all installed models.
By default, auto-created models (i.e., m2m models without an
explicit intermediate table) are not included. However, if you
specify include_auto_created=True, they will be.
By default, models created to satisfy deferred attribute
queries are *not* included in the list of models. However, if
you specify include_deferred, they will be.
"""
cache_key = (app_mod, include_auto_created, include_deferred)
try:
return self._get_models_cache[cache_key]
except KeyError:
pass
self._populate()
if app_mod:
app_list = [self.app_models.get(app_mod.__name__.split('.')[-2], SortedDict())]
else:
app_list = self.app_models.itervalues()
model_list = []
for app in app_list:
model_list.extend(
model for model in app.values()
if ((not model._deferred or include_deferred)
and (not model._meta.auto_created or include_auto_created))
)
self._get_models_cache[cache_key] = model_list
return model_list
def get_model(self, app_label, model_name, seed_cache=True):
"""
Returns the model matching the given app_label and case-insensitive
model_name.
Returns None if no model is found.
"""
if seed_cache:
self._populate()
return self.app_models.get(app_label, SortedDict()).get(model_name.lower())
def register_models(self, app_label, *models):
"""
Register a set of models as belonging to an app.
"""
for model in models:
# Store as 'name: model' pair in a dictionary
# in the app_models dictionary
model_name = model._meta.object_name.lower()
model_dict = self.app_models.setdefault(app_label, SortedDict())
if model_name in model_dict:
# The same model may be imported via different paths (e.g.
# appname.models and project.appname.models). We use the source
# filename as a means to detect identity.
fname1 = os.path.abspath(sys.modules[model.__module__].__file__)
fname2 = os.path.abspath(sys.modules[model_dict[model_name].__module__].__file__)
# Since the filename extension could be .py the first time and
# .pyc or .pyo the second time, ignore the extension when
# comparing.
if os.path.splitext(fname1)[0] == os.path.splitext(fname2)[0]:
continue
model_dict[model_name] = model
self._get_models_cache.clear()
cache = AppCache()
# These methods were always module level, so are kept that way for backwards
# 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
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