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'''
Created on Apr 10, 2012
@author: leifj
'''
from django.db import models
from django.db.models.fields import DateTimeField
from django.contrib.contenttypes.models import ContentType
from django.contrib.contenttypes import generic
from django_extensions.db.fields import UUIDField
from django.dispatch.dispatcher import receiver
from django.db.models.signals import post_save, pre_delete
from django.core.exceptions import ObjectDoesNotExist
from django.db.models.base import ModelBase
class NotAModel(Exception):
pass
class RecursiveRegistration(Exception):
pass
class UninitializedObject(Exception):
pass
class Resource(models.Model):
uuid = UUIDField(unique=True)
content_type = models.ForeignKey(ContentType)
object_id = models.PositiveIntegerField()
content_object = generic.GenericForeignKey('content_type', 'object_id')
lastupdated = DateTimeField(auto_now=True)
timecreated = DateTimeField(auto_now_add=True)
def __unicode__(self):
return self.uuid
def object_for_uuid(uuid):
try:
r = Resource.objects.get(uuid=uuid)
return r.content_object
except ObjectDoesNotExist:
return None
def uuid_for_object(o):
if not o.id:
raise UninitializedObject("Can't obtain uuid for non-persisted objects")
typ = ContentType.objects.get_for_model(o)
r,cr = Resource.objects.get_or_create(object_id=o.id,content_type=typ)
return r.uuid
def add_resource(o):
typ = ContentType.objects.get_for_model(o)
r,cr = Resource.objects.get_or_create(object_id=o.id,content_type=typ)
return r.uuid
def delete_resource(o):
typ = ContentType.objects.get_for_model(o)
try:
r = Resource.objects.get(object_id=o.id,content_type=typ)
r.delete()
except ObjectDoesNotExist:
pass
class ResourceClassRegistry():
def __init__(self):
self._registry = []
def register(self,model,addField=True):
if not isinstance(model,ModelBase):
raise NotAModel('%s does not appear to be a model!' % model)
if not model in self._registry:
if addField:
setattr(model,'uuid',property(lambda x: uuid_for_object(x)))
self._registry.append(model)
resources = ResourceClassRegistry()
def register(model):
resources.register(model)
@receiver(post_save)
def auto_create_resource(sender,**kwargs):
if sender in resources._registry and kwargs['created']:
add_resource(kwargs['instance'])
@receiver(pre_delete)
def auto_delete_resource(sender,**kwargs):
if sender in resources._registry:
delete_resource(kwargs['instance'])
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