Find documents including element in Array field with mongomapper?

Question

I am new to mongodb/mongomapper and can't find an answer to this.

I have a mongomapper class with the following fields

key :author_id, Integer
key :partecipant_ids, Array

Let's say I have a "record" with the following attributes:

{ :author_id => 10, :partecipant_ids => [10,15,201] }

I want to retrieve all the objects where the partecipant with id 15 is involved. I did not find any mention in the documentation.

The strange thing is that previously I was doing this query

MessageThread.where :partecipant_ids => [15]

which worked, but after (maybe) some change in the gem/mongodb version it stopped working. Unfortunately I don't know which version of mongodb and mongomapper I was using before.

What version of rails/mongomapper/mongodb etc are you using now? — Tyler Brock
– Tyler Brock, Commented Nov 28, 2011 at 15:14

Brian Hempel · Accepted Answer · 2011-11-28 15:32:51Z

8

In the current versions of MongoMapper, this will work:

MessageThread.where(:partecipant_ids => 15)

And this should work as well...

MessageThread.where(:partecipant_ids => [15])

...because plucky autoexpands that to:

MessageThread.where(:partecipant_ids => { :$in => [15] })

(see https://github.com/jnunemaker/plucky/blob/master/lib/plucky/criteria_hash.rb#L121)

I'd say take a look at your data and try out queries in the Mongo console to make sure you have a working query. MongoDB queries translate directly to MM queries except for the above (and a few other minor) caveats. See http://www.mongodb.org/display/DOCS/Querying

answered Nov 28, 2011 at 15:32

Brian Hempel

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3 Comments

Brian Hempel Over a year ago

Also see the plucky tests, they are probably clearer to read than the source: github.com/jnunemaker/plucky/blob/master/test/plucky/…

Stefano Lampis Over a year ago

strange fact. With MessageThread.where(:partecipant_ids => ['15']) it works. For some reason it's treated like an array of strings now? I am 100% sure that before the upgrade it was working with integers.

Brian Hempel Over a year ago

You can try adding :typecast => 'Integer' to your :partecipant_ids key. I'm not sure if that will break the many :in association.

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