CODEWITHSUNDEEP
ruby-on-railsrubymongodbmongoid
Robin Rosicky
Robin Rosicky

Reputation: 325

Ruby map/collect is slow on a large Mongoid collection

I have a Mongoid collection on which I run a where query.

Now, I would like to build an array containing a values of a specific field from all the documents in the collection.

e.g. if my Monogid model is 

class Foo
    field :color, type: String
end

I'd like to do something like this -

red_ducks = Foo.where(color: 'red')
red_duck_ids = red_ducks.map(&:_id)

Unfortunately, when the result of the query is large it takes a long time. It takes 6 seconds for 10,000 documents in my case, for example.

Is there any way to speed this up?

Upvotes: 1

Views: 705

Answers (2)

Kostas Rousis
Kostas Rousis

Reputation: 6068

Can't you just call distinct on your scope with _id as an attribute?

red_duck_ids = Foo.where(color: 'red').distinct(:_id)

Which will return you a list of all _ids that meet your conditions. You can find more information on Mongo's distinct documentation.

You can also have a look at only and if you are using version 3.1 or newer you can also use Criteria#pluck.

Upvotes: 2

a14m
a14m

Reputation: 8055

have you tried

Foo.where(color: 'red').pluck(:id)

might be faster (not sure)

Upvotes: 1

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