How to get something random in datastore (AppEngine)?

Question

Currently i\'m using something like this:

    images = Image.all()
    count = images.count()
    random_numb = random.randrange(1, count)
    image = Image.         


        

Answer 1

Another solution (if you don't want to add an additional property). Keep a set of keys in memory.

import random

# Get all the keys, not the Entities
q = ItemUser.all(keys_only=True).filter('is_active =', True)
item_keys = q.fetch(2000) 

# Get a random set of those keys, in this case 20 
random_keys = random.sample(item_keys, 20)

# Get those 20 Entities
items = db.get(random_keys)

The above code illustrates the basic method for getting only keys and then creating a random set with which to do a batch get. You could keep that set of keys in memory, add to it as you create new ItemUser Entities, and then have a method that returns a n random Entities. You'll have to implement some overhead to manage the memcached keys. I like this solution better if you're performing the query for random elements often (I assume using a batch get for n Entities is more efficient than a query for n Entities).