GAE datastore query with filter and sort using objectify

Question

I am trying to query the datastore for the top 100 users in terms of points scored, who have logged on in the past week (the date field).

List use         


        

Answer 1

You may want to consider an alternate approach. This is a lot of index overhead which will cause your costs to be higher, the response time for the handler executing this function to operate an order of magnitude slower, and you will have moments where the eventual consistency of index updates will affect maintenance of this data. If you have a busy site, you will surely not be happy with the latency and costs associated with this approach.

There are a number of alternate approaches. Your expected site transactions per second would affect which you choose. Here is a very simple alternative. Create an ndb entity with a TextProperty. Serialize the top scores entries using a string such as score_userid. Store them in the text field by joining them with a unique character. When a new score comes in, use get_by_id to retrieve this record (ndb automatically handles memcaching for you). Split it into an array. Split the last element of the array, and check against the new score. If it is less than the score, drop it, and append the new score_userid string to the array. Sort the array, join it, and put() the new TextProperty. If you want you could set up an end of the day cron to scan your scores for the day to check to see if your process was affected by the very small chance that two scores arrived at nearly the same time causing one to overwrite the other. HTH. -stevep