/
sourcegroups.py
179 lines (140 loc) · 6.17 KB
/
sourcegroups.py
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"""
Source groups are the means by which image spec sources are identified. They
have two responsibilities:
1. To dispatch ``source_saved`` signals. (These will be relayed to the
corresponding specs' cache file strategies.)
2. To provide the source files that they represent, via a generator method named
``files()``. (This is used by the generateimages management command for
"pre-caching" image files.)
"""
import inspect
from django.db.models.signals import post_init, post_save
from django.utils.functional import wraps
from ..cachefiles import LazyImageCacheFile
from ..signals import source_saved
from ..utils import get_nonabstract_descendants
def ik_model_receiver(fn):
"""
A method decorator that filters out signals coming from models that don't
have fields that function as ImageFieldSourceGroup sources.
"""
@wraps(fn)
def receiver(self, sender, **kwargs):
if not inspect.isclass(sender):
return
for src in self._source_groups:
if issubclass(sender, src.model_class):
fn(self, sender=sender, **kwargs)
# If we find a match, return. We don't want to handle the signal
# more than once.
return
return receiver
class ModelSignalRouter:
"""
Normally, ``ImageFieldSourceGroup`` would be directly responsible for
watching for changes on the model field it represents. However, Django does
not dispatch events for abstract base classes. Therefore, we must listen for
the signals on all models and filter out those that aren't represented by
``ImageFieldSourceGroup``s. This class encapsulates that functionality.
Related:
https://github.com/matthewwithanm/django-imagekit/issues/126
https://code.djangoproject.com/ticket/9318
"""
def __init__(self):
self._source_groups = []
uid = 'ik_spec_field_receivers'
post_init.connect(self.post_init_receiver, dispatch_uid=uid)
post_save.connect(self.post_save_receiver, dispatch_uid=uid)
def add(self, source_group):
self._source_groups.append(source_group)
def init_instance(self, instance):
instance._ik = getattr(instance, '_ik', {})
def update_source_hashes(self, instance):
"""
Stores hashes of the source image files so that they can be compared
later to see whether the source image has changed (and therefore whether
the spec file needs to be regenerated).
"""
self.init_instance(instance)
instance._ik['source_hashes'] = {
attname: hash(getattr(instance, attname))
for attname in self.get_source_fields(instance)}
return instance._ik['source_hashes']
def get_source_fields(self, instance):
"""
Returns a list of the source fields for the given instance.
"""
return {
src.image_field
for src in self._source_groups
if isinstance(instance, src.model_class)}
@ik_model_receiver
def post_save_receiver(self, sender, instance=None, created=False, update_fields=None, raw=False, **kwargs):
if not raw:
self.init_instance(instance)
old_hashes = instance._ik.get('source_hashes', {}).copy()
new_hashes = self.update_source_hashes(instance)
for attname in self.get_source_fields(instance):
if update_fields and attname not in update_fields:
continue
file = getattr(instance, attname)
if file and old_hashes.get(attname) != new_hashes[attname]:
self.dispatch_signal(source_saved, file, sender, instance,
attname)
@ik_model_receiver
def post_init_receiver(self, sender, instance=None, **kwargs):
self.init_instance(instance)
source_fields = self.get_source_fields(instance)
local_fields = {
field.name: field
for field in instance._meta.local_fields
if field.name in source_fields}
instance._ik['source_hashes'] = {
attname: hash(file_field)
for attname, file_field in local_fields.items()}
def dispatch_signal(self, signal, file, model_class, instance, attname):
"""
Dispatch the signal for each of the matching source groups. Note that
more than one source can have the same model and image_field; it's
important that we dispatch the signal for each.
"""
for source_group in self._source_groups:
if issubclass(model_class, source_group.model_class) and source_group.image_field == attname:
signal.send(sender=source_group, source=file)
class ImageFieldSourceGroup:
"""
A source group that repesents a particular field across all instances of a
model and its subclasses.
"""
def __init__(self, model_class, image_field):
self.model_class = model_class
self.image_field = image_field
signal_router.add(self)
def files(self):
"""
A generator that returns the source files that this source group
represents; in this case, a particular field of every instance of a
particular model and its subclasses.
"""
for model in get_nonabstract_descendants(self.model_class):
for instance in model.objects.all().iterator():
yield getattr(instance, self.image_field)
class SourceGroupFilesGenerator:
"""
A Python generator that yields cache file objects for source groups.
"""
def __init__(self, source_group, generator_id):
self.source_group = source_group
self.generator_id = generator_id
def __eq__(self, other):
return (isinstance(other, self.__class__)
and self.__dict__ == other.__dict__)
def __ne__(self, other):
return not self.__eq__(other)
def __hash__(self):
return hash((self.source_group, self.generator_id))
def __call__(self):
for source_file in self.source_group.files():
yield LazyImageCacheFile(self.generator_id,
source=source_file)
signal_router = ModelSignalRouter()