forum/models/utils.py

   1 from django.db import models
   2 from django.core.cache import cache
   3 from django.conf import settings
   4 from django.utils.encoding import force_unicode
   5
   6 try:
   7     from cPickle import loads, dumps
   8 except ImportError:
   9     from pickle import loads, dumps
  10
  11 from copy import deepcopy
  12 from base64 import b64encode, b64decode
  13 from zlib import compress, decompress
  14
  15
  16 class PickledObject(str):
  17     pass
  18
  19 def dbsafe_encode(value, compress_object=True):
  20     if not compress_object:
  21         value = b64encode(dumps(deepcopy(value)))
  22     else:
  23         value = b64encode(compress(dumps(deepcopy(value))))
  24     return PickledObject(value)
  25
  26 def dbsafe_decode(value, compress_object=True):
  27     if not compress_object:
  28         value = loads(b64decode(value))
  29     else:
  30         value = loads(decompress(b64decode(value)))
  31     return value
  32
  33 class PickledObjectField(models.Field):
  34     __metaclass__ = models.SubfieldBase
  35
  36     def __init__(self, *args, **kwargs):
  37         self.compress = kwargs.pop('compress', True)
  38         self.protocol = kwargs.pop('protocol', 2)
  39         kwargs.setdefault('null', True)
  40         kwargs.setdefault('editable', False)
  41         super(PickledObjectField, self).__init__(*args, **kwargs)
  42
  43     def get_default(self):
  44         if self.has_default():
  45             if callable(self.default):
  46                 return self.default()
  47             return self.default
  48
  49         return super(PickledObjectField, self).get_default()
  50
  51     def to_python(self, value):
  52         if value is not None:
  53             try:
  54                 value = dbsafe_decode(value, self.compress)
  55             except:
  56                 if isinstance(value, PickledObject):
  57                     raise
  58         return value
  59
  60     def get_db_prep_value(self, value):
  61         if value is not None and not isinstance(value, PickledObject):
  62             value = force_unicode(dbsafe_encode(value, self.compress))
  63         return value
  64
  65     def value_to_string(self, obj):
  66         value = self._get_val_from_obj(obj)
  67         return self.get_db_prep_value(value)
  68
  69     def get_internal_type(self):
  70         return 'TextField'
  71
  72     def get_db_prep_lookup(self, lookup_type, value):
  73         if lookup_type not in ['exact', 'in', 'isnull']:
  74             raise TypeError('Lookup type %s is not supported.' % lookup_type)
  75         return super(PickledObjectField, self).get_db_prep_lookup(lookup_type, value)
  76
  77
  78 class KeyValueManager(models.Manager):
  79
  80     def create_cache_key(self, key):
  81         return "%s:keyvalue:%s" % (settings.APP_URL, key)
  82
  83     def save_to_cache(self, instance):
  84         cache.set(self.create_cache_key(instance.key), instance, 2592000)
  85
  86     def remove_from_cache(self, instance):
  87         cache.delete(self.create_cache_key(instance.key))
  88
  89     def get(self, **kwargs):
  90         if 'key' in kwargs:
  91             instance = cache.get(self.create_cache_key(kwargs['key']))
  92
  93             if instance is None:
  94                 instance = super(KeyValueManager, self).get(**kwargs)
  95                 self.save_to_cache(instance)
  96
  97             return instance
  98
  99         else:
 100             return super(KeyValueManager, self).get(**kwargs)
 101
 102 class KeyValue(models.Model):
 103     key = models.CharField(max_length=255, unique=True)
 104     value = PickledObjectField()
 105
 106     objects = KeyValueManager()
 107
 108     class Meta:
 109         app_label = 'forum'
 110
 111     def save(self, *args, **kwargs):
 112         super(KeyValue, self).save(*args, **kwargs)
 113         KeyValue.objects.save_to_cache(self)
 114
 115     def delete(self):
 116         KeyValue.objects.remove_from_cache(self)
 117         super(KeyValue, self).delete()