django-rest-framework mixin that caches serialization output with cache key based on DateTimeField(auto_now=True)

mixins.py

# License: MIT
# django-rest-framework mixin

class CachedReprMixin(serializers.ModelSerializer):
    '''
    mixin for ModelSerializer subclass whose model has a 'modified' field.
    assuming the model has a 'modified' field:

        modified = models.DateTimeField(auto_now=True)

    the core assumption is that if there is a change to the object, the value
    of 'modified' will be different. which makes it very interesting for
    creating a cache key.
    '''
    def to_representation(self, obj):
        '''
        custom function to deal with obj representation.
        we are trying to cut down number of queries, so use cache
        where possible.
        '''
        # only handle single objects
        if not isinstance(obj, list):
            # we want to distinguish based on:
            # 1. serializer (different serializer = different fields)
            # 2. model and pk (different object = different key)
            # 3. modified field (different dates = different fields)
            key = '{0.__class__.__name__}:{1.__class__.__name__}:{1.pk}:{2}'
            try:
                obj_key = key.format(self, obj, obj.modified.strftime('%s'))
                data = CACHE.get(obj_key, None)
                if data is None:
                    LOG.info('cache miss: %s', obj_key)
                    data = super(CachedReprMixin, self).to_representation(obj)
                    CACHE.set(obj_key, json.dumps(data), timeout=None)
                else:
                    LOG.info('cache hit: %s', obj_key)
                    data = json.loads(data)
                return data
            except AttributeError:
                # don't have a modified field.
                pass
        # default serialization if cannot use the cache.
        return super(CachedReprMixin, self).to_representation(obj)