Retrieve list of mongo documents by ids preserving order

Which is the best way to retrieve a list of mongodb documents using mongoid in the order specified in the list.

My current solution is:

docs = Doc.where(:_id.in => ids).sort { |x, y| ids.index(x.id) <=> ids.index(y.id) }

It seems there should be a better solution for this using mongoid que开发者_开发技巧ry interface. Any ideas?

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If the number of ids is small you might get away with this (no need to sort it though):

docs = ids.map { |id| Doc.find(id) }

The drawback is of course that it will still go to the database for every document.

The closest method I could find is Doc.criteria.for_ids(ids) but it will not honor the order of the ids and fetch every document only once. See this question.