code: def where(constraints = nil)
        return query.compile_where unless constraints.is_a?(Hash)
        query.where constraints
        query
      end
docs: Apply a set of constraints.
   @param constraints [Hash] the set of {Parse::Query} cosntraints
   @return [Hash] if no constraints were passed, returns a compiled query.
   @return [Parse::Query] if constraints were passed, returns the chainable query.