Question

I am using Ruby code to calculate sum from the array returned by Mongoid.

But maybe using Map/Reduce can be faster, except I don’t see any docs for Map Reduce on mongoid.org and Google for

map reduce site:mongoid.org

doesn’t give any result either. (or using MapReduce or Map/Reduce)

There are docs on MongoDB’s site

map reduce site:mongodb.org

but need to use Map Reduce with Mongoid as well.

Answer 1

You can use map reduce with Mongoid just as you could through the Ruby driver directly:

# Post is a Mongoid model...
Post.collection.map_reduce(map_function, reduce_function, options)

For some examples of doing map reduce in the Ruby driver, see this blog post by Kyle Banker (maintainer of the Ruby MongoDB driver).