Retrieving array of ids in Mongoid

Question

how do you retrieve an array of IDs in Mongoid?

arr=["id1","id2"] User.where(:id=>arr) 

You can do this easily if you are retrieving another attribute

User.where(:nickname.in=>["kk","ll"]) 

But I am wondering how to do this in mongoid -> this should be a very simple and common operation

Answer 1

Remember that the ID is stored as :_id and not :id . There is an id helper method, but when you do queries, you should use :_id:

User.where(:_id.in => arr) 

Often I find it useful to get a list of ids to do complex queries, so I do something like:

user_ids = User.only(:_id).where(:foo => :bar).distinct(:_id) Post.where(:user_id.in => user_ids) 

Answer 2

Or simply:

arr = ['id1', 'id2', 'id3'] User.find(arr)