osqa/forum/models/utils.py

   1 from django.db import models
   2 from django.core.cache import cache
   3 from django.conf import settings
   4 #try:
   5 #       import cPickle as pickle
   6 #except ImportError:
   7 import pickle
   8 import django.dispatch
   9
  10 class PickledObject(str):
  11         pass
  12
  13 class PickledObjectField(models.Field):
  14     __metaclass__ = models.SubfieldBase
  15
  16     def to_python(self, value):
  17         if isinstance (value, PickledObject):
  18             return value
  19
  20         try:
  21             return pickle.loads(value.encode('utf-8'))
  22         except:
  23             return value
  24
  25     def get_db_prep_save(self, value):
  26         if value is not None:
  27             if isinstance(value, PickledObject):
  28                 return str(value)
  29             else:
  30                             value = pickle.dumps(value)
  31
  32         return value
  33
  34     def get_internal_type(self):
  35         return 'TextField'
  36
  37
  38 class KeyValueManager(models.Manager):
  39
  40     def create_cache_key(self, key):
  41         return "%s:key_value:%s" % (settings.APP_URL, key)
  42
  43     def save_to_cache(self, instance):
  44         cache.set(self.create_cache_key(instance.key), instance, 2592000)
  45
  46     def remove_from_cache(self, instance):
  47         cache.delete(self.create_cache_key(instance.key))
  48
  49     def get(self, **kwargs):
  50         if 'key' in kwargs:
  51             instance = cache.get(self.create_cache_key(kwargs['key']))
  52
  53             if instance is None:
  54                 instance = super(KeyValueManager, self).get(**kwargs)
  55                 self.save_to_cache(instance)
  56
  57             return instance
  58
  59         else:
  60             return super(KeyValueManager, self).get(**kwargs)
  61
  62 class KeyValue(models.Model):
  63     key = models.CharField(max_length=255, unique=True)
  64     value = PickledObjectField()
  65
  66     objects = KeyValueManager()
  67
  68     class Meta:
  69         app_label = 'forum'
  70
  71     def save(self, *args, **kwargs):
  72         super(KeyValue, self).save(*args, **kwargs)
  73         KeyValue.objects.save_to_cache(self)
  74
  75     def delete(self):
  76         KeyValue.objects.remove_from_cache(self)
  77         super(KeyValue, self).delete()