QuerysetCache

InstanceCache is useful for caching single instance of a model. If you want to cache some queryset’s result of model or some descendent query of that model’s queryset. E.g. existance check or count query. You should use QuerysetCache.

from flash import QuerysetCache

class ParticipationListCacheOnUser(QuerysetCache):
    model = Participation
    key_fields = ('user',)

# Using cache class
participation_list = ParticipationListCacheOnUser(user=user).resolve()

The above class will cache list of all participants for a single user. You may cache some descendent query result too. E.g. If you want to cache the list of event ids a user have participated in then you can define it by overriding default get_result method.

class ParticipatedEventIdListCacheOnUser(QuerysetCache):
    model = Participation
    key_fields = ('user',)

    def get_result(self, user):
        event_ids = self.get_queryset().filter(user=user).values_list(
                        'event', flat=True)
        return event_ids

event_ids = ParticipatedEventIdListCacheOnUser(user).resolve()

Or if you want to cache the count of the participation of single user

class ParticipationCountCacheOnUser(QuerysetCache):
    model = Participation
    key_fields = ('user',)

    def get_result(self, user):
        return self.get_queryset().filter(user=user).count()

participation_count = ParticipationCountCacheOnUser(user).resolve()

You can also use ModelCacheManger to define default QuerysetCache. E.g. ParticipationListCacheOnUser’s behaviour can be achieved by

class ParticipationCacheManager(ModelCacheManger):
    model = Participation
    get_key_fields_list = [
        ('user', 'event')
    ]
    filter_key_fields_list = [
        ('user',),
    ]

participation_list = Participation.cache.filter(user=user)

You can also define some supporting methods on ParticipationCacheManager class for other cache classes defined above

class ParticipationCacheManager(ModelCacheManger):
    model = Participation
    get_key_fields_list = [
        ('user', 'event')
    ]
    filter_key_fields_list = [
        ('user',),
    ]

    def get_count_for_user(self, user):
        return ParticipationCountCacheOnUser(user).resolve()

    def get_event_id_list_for_user(self, user):
        return ParticipatedEventIdListCacheOnUser(user).resolve()

# Use the methods
participation_count = Participation.cache.get_count_for_user(user)
event_ids = Participation.cache.get_event_id_list_for_user(user)

Some notes:

• When overriding get_result method, remember that return value should not be some lazy queryset object. Use list() builitn function to retrieve the list first before returning the queryset result in that case.