GAE Query counter (+1000)

How to implement this query counter into existing class? The main purpose is i have datastore model of members with more than 3000 records. I just want to count its total record, and found t开发者_如何学运维his on app engine cookbook:

def query_counter (q, cursor=None, limit=500):
    if cursor:
        q.with_cursor (cursor)
    count = q.count (limit=limit)
    if count == limit:
        return count + query_counter (q, q.cursor (), limit=limit)
    return count

My existing model is:

class Members(search.SearchableModel):
    group = db.ListProperty(db.Key,default=[])
    email = db.EmailProperty()
    name = db.TextProperty()
    gender = db.StringProperty()

Further i want to count members that join certain group with list reference. It might content more than 1000 records also.

Anyone have experience with query.cursor for this purpose?

To find all members you would use it like this:

num_members = query_counter(Members.all())

However, you may find that this runs slowly, because it's making a lot of datastore calls.

A faster way would be to have a separate model class (eg MembersCount), and maintain the count in there (ie add 1 when you create a member, subtract 1 when you delete a member).

If you are creating and deleting members frequently you may need to create a sharded counter in order to get good performance - see here for details:

http://code.google.com/appengine/articles/sharding_counters.html

To count members in a certain group, you could do something like this:

group = ...
num_members = query_counter(Members.all().filter('group =', group.key()))

If you expect to have large numbers of members in a group, you could also do that more efficiently by using a counter model which is sharded by the group.