Abstract Random AppEngine ndb.Model. Extend this class and use .random method to get random entities/records.

randommodel.py

import random
from google.appengine.ext import ndb


class RandomIndexedModel(ndb.Model):
  """Abstracts how we do randomness in the other models."""
  random_index = ndb.FloatProperty('ri')

  @classmethod
  def random(cls, count=1, exclude=None, ancestor=None, filters=None):
    exclude = exclude or []
    filters = filters or []
    # Get the count requested plus the excluded size and programatically
    # remove the exclude list and return exactly the count requested.
    extra_count = count+len(exclude)
    query = cls.query(ancestor=ancestor) if ancestor else cls.query()
    
    # If any filters is passed add it to the query.
    for query_filter in filters:
      query = query.filter(query_filter)

    entities = query.filter(
        cls.random_index >= random.random()).fetch(extra_count)

    # If that fetch got less than count, get entities from the top of the list.
    if not entities or len(entities) < extra_count:
      entities = query.order(cls.random_index).fetch(extra_count)

    # Remove exclude and return exact count.
    entities = list(entity for entity in entities if not entity.key in exclude)
    return entities[:count]

  def _pre_put_hook(self):
    self.random_index = random.random()