code: def all(constraints = {})
        q = query( {limit: :max}.merge(constraints) )
        if block_given?
          # if we have a query, then use the Proc with it (more efficient)
          return q.present? ? q.results(&Proc.new) : collection.each(&Proc.new)
        end
        # if no block given, get all the results
        q.present? ? q.results : collection
      end
docs: You can get items within the collection relation filtered by a specific set
   of query constraints.