from collections import defaultdict
from django.apps import apps
from django.db import models
from django.utils.translation import gettext_lazy as _
class ContentTypeManager(models.Manager):
use_in_migrations = True
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
# Cache shared by all the get_for_* methods to speed up
# ContentType retrieval.
self._cache = {}
def get_by_natural_key(self, app_label, model):
try:
ct = self._cache[self.db][(app_label, model)]
except KeyError:
ct = self.get(app_label=app_label, model=model)
self._add_to_cache(self.db, ct)
return ct
def _get_opts(self, model, for_concrete_model):
if for_concrete_model:
model = model._meta.concrete_model
return model._meta
def _get_from_cache(self, opts):
key = (opts.app_label, opts.model_name)
return self._cache[self.db][key]
def get_for_model(self, model, for_concrete_model=True):
"""
Return the ContentType object for a given model, creating the
ContentType if necessary. Lookups are cached so that subsequent lookups
for the same model don't hit the database.
"""
opts = self._get_opts(model, for_concrete_model)
try:
return self._get_from_cache(opts)
except KeyError:
pass
# The ContentType entry was not found in the cache, therefore we
# proceed to load or create it.
try:
# Start with get() and not get_or_create() in order to use
# the db_for_read (see #20401).
ct = self.get(app_label=opts.app_label, model=opts.model_name)
except self.model.DoesNotExist:
# Not found in the database; we proceed to create it. This time
# use get_or_create to take care of any race conditions.
ct, created = self.get_or_create(
app_label=opts.app_label,
model=opts.model_name,
)
self._add_to_cache(self.db, ct)
return ct
def get_for_models(self, *models, for_concrete_models=True):
"""
Given *models, return a dictionary mapping {model: content_type}.
"""
results = {}
# Models that aren't already in the cache.
needed_app_labels = set()
needed_models = set()
# Mapping of opts to the list of models requiring it.
needed_opts = defaultdict(list)
for model in models:
opts = self._get_opts(model, for_concrete_models)
try:
ct = self._get_from_cache(opts)
except KeyError:
needed_app_labels.add(opts.app_label)
needed_models.add(opts.model_name)
needed_opts[opts].append(model)
else:
results[model] = ct
if needed_opts:
# Lookup required content types from the DB.
cts = self.filter(
app_label__in=needed_app_labels,
model__in=needed_models
)
for ct in cts:
model = ct.model_class()
opts_models = needed_opts.pop(ct.model_class()._meta, [])
for model in opts_models:
results[model] = ct
self._add_to_cache(self.db, ct)
# Create content types that weren't in the cache or DB.
for opts, opts_models in needed_opts.items():
ct = self.create(
app_label=opts.app_label,
model=opts.model_name,
)
self._add_to_cache(self.db, ct)
for model in opts_models:
results[model] = ct
return results
def get_for_id(self, id):
"""
Lookup a ContentType by ID. Use the same shared cache as get_for_model
(though ContentTypes are obviously not created on-the-fly by get_by_id).
"""
try:
ct = self._cache[self.db][id]
except KeyError:
# This could raise a DoesNotExist; that's correct behavior and will
# make sure that only correct ctypes get stored in the cache dict.
ct = self.get(pk=id)
self._add_to_cache(self.db, ct)
return ct
def clear_cache(self):
"""
Clear out the content-type cache.
"""
self._cache.clear()
def _add_to_cache(self, using, ct):
"""Insert a ContentType into the cache."""
# Note it's possible for ContentType objects to be stale; model_class() will return None.
# Hence, there is no reliance on model._meta.app_label here, just using the model fields instead.
key = (ct.app_label, ct.model)
self._cache.setdefault(using, {})[key] = ct
self._cache.setdefault(using, {})[ct.id] = ct
class ContentType(models.Model):
app_label = models.CharField(max_length=100)
model = models.CharField(_('python model class name'), max_length=100)
objects = ContentTypeManager()
class Meta:
verbose_name = _('content type')
verbose_name_plural = _('content types')
db_table = 'django_content_type'
unique_together = (('app_label', 'model'),)
def __str__(self):
return self.name
@property
def name(self):
model = self.model_class()
if not model:
return self.model
return str(model._meta.verbose_name)
def model_class(self):
"""Return the model class for this type of content."""
try:
return apps.get_model(self.app_label, self.model)
except LookupError:
return None
def get_object_for_this_type(self, **kwargs):
"""
Return an object of this type for the keyword arguments given.
Basically, this is a proxy around this object_type's get_object() model
method. The ObjectNotExist exception, if thrown, will not be caught,
so code that calls this method should catch it.
"""
return self.model_class()._base_manager.using(self._state.db).get(**kwargs)
def get_all_objects_for_this_type(self, **kwargs):
"""
Return all objects of this type for the keyword arguments given.
"""
return self.model_class()._base_manager.using(self._state.db).filter(**kwargs)
def natural_key(self):
return (self.app_label, self.model)