Rails Mongoid `pluck` equivalent?

Question

In my Rails app I am using MongoID with a Elasticsearch river for text search.

For @devices_with_config = ConfigTextSearch.search params[:device_id] I want to extract just the device_id fields for the matching records in the query. In mongoID 3.1.0 I could just use Band.all.pluck(:name). But unfortunately, I am stuck with 3.0.23.

I see there is a similar moped expression collections[:bands].find.select(name: 1)...but I am new to rails and can't figure out how I would use a moped expression in a controller or model.

Any Ideas on how I can just extract the 'device_id' field in matches with MongoId?

Mike S · Answer 1 · 2015-03-05T21:59:12.940

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Mongoid has a pluck function now.

mongoid#pluck

edited Mar 05 '15 at 21:59

answered Mar 05 '15 at 16:40

Mike S

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score 1 · Answer 2 · answered Jan 14 '15 at 19:39

1

You can get a hold of a Moped collection like this

 Band.collection.find.select(name: 1)

answered Jan 14 '15 at 19:39

Sergio Tulentsev

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Thanks. With `ConfigTextSearch.search("foo").find.select(device_id: 1)` I get `ArgumentError: wrong number of arguments (1 for 0) from (pry):46:in `select'` – dman Jan 14 '15 at 19:44
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`ConfigTextSearch.search("foo")` does not look like a moped collection to me. – Sergio Tulentsev Jan 14 '15 at 19:46
It is using `elasticsearch-rails`, which inherits the methods from MongoId. – dman Jan 14 '15 at 19:49
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Didn't work with elasticsearch, so you're on your own here, sorry :) – Sergio Tulentsev Jan 14 '15 at 19:50

score 1 · Answer 3 · answered Jul 27 '15 at 06:21

It seems like you're not actually building a Mongoid criteria with that call, but I haven't looked into elasticsearch-rails so I can't be 100% sure.

If you're completely unable to update to 3.1.0 you should be able to just monkey patch this functionality in.

module Mongoid
  class Criteria
    # select specific fields from collection based on current scope, returned as a hash
    def pluck(*fields)
      raise ArgumentError, 'Call this with at least one field' if fields.empty?

      collection.find(self.selector).select(Hash[fields.map { |field| [field, 1] }]).to_a
    end
  end
end

After adding the above code you should be able to do the following:

Band.where(name: 'awesome').pluck(:id, :device_id)

score 1 · Answer 4 · answered Jul 28 '15 at 09:59

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An equivalent to the pluck method defined in mongoid is:

plucked_array = User.where(:name => 'xyz').map(&: field_to_be_plucked)

Where field_to_be_plucked is the name of the field whose values need to be plucked out in Array.

answered Jul 28 '15 at 09:59

Pushp Raj Saurabh

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This is loading the whole document (and embedded documents) from mongodb which is pretty inefficient, a better implementation if you're forced to use `map` would be: `User.where(name: 'xyz').only(:email).map(&:email)` which will only load the one field you're looking at :) – Jay Aug 10 '15 at 01:38

score 0 · Answer 5 · answered Jan 15 '15 at 13:50

0

Found it....from what I can tell this isn't on the MongoId docs.....

sue = bob.results.map { |r| r._source.device_id }

answered Jan 15 '15 at 13:50

dman

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score 0 · Answer 6 · answered Sep 14 '16 at 14:55

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What I used for the same purpose, with Mongoid 3.0 :

Band.all.distinct(:name)

Warning: relevant only if all the names are different (of if you want to remove duplicates).

answered Sep 14 '16 at 14:55

Brilnius

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This really does not answer the question. – Daniel Wisehart Sep 14 '16 at 15:15
I disagree. This solution works (with the limitation I gave as a warning).In my opinion, it seems preferable compared to solution where the rows are iterated in memory (e.g. using map()). – Brilnius Dec 02 '16 at 12:59

Rails Mongoid `pluck` equivalent?

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