Question

I am trying to use map_reduce on a collection, via the ruby console , but I am getting “NoMethodError: undefined method `map_reduce’ for #

results = Thing.collection.map_reduce(map, reduce, out: "vr")

Answer 1

Map Reduce in Mongoid 3 works slightly differently. The syntax you have would work for the mongo ruby driver. In Mongoid 3, you call this off the class or criteria, like the following:

From a criteria:

Model.where(field: value).map_reduce(map, reduce).out(inline: true)

From a class:

SomeClass.map_reduce(map, reduce).out(replace: "mr-results").each do |document|
  #do something
end

You can find more information on this in the Mongoid docs