Question

I am trying to use AppEngine-MapReduce. I understand how to perform an operation over all entities of some entity_kind, but what is the easiest way to only operate on entities over a data range when the entity has a date attribute? Is there a simple way to pass parameters to the mapper?

For example, what if I only wanted to delete entities where:

entity.created >= start and entity.created < stop

class Entity(db.Model):
  created = db.DateTimeProperty()

from mapreduce import operation as op
def process(entity):
  yield op.db.Delete(entity)

Answer 1

Currently there’s no way to iterate over a query in a mapreduce – you have to iterate over every entity of the given kind. Instead, you should apply the filter in the map function, and only delete entities that match.