def where(constraints = nil)
      return query.compile_where unless constraints.is_a?(Hash)
      query.where constraints
      query
    end
def where(constraints = nil)
      return query.compile_where unless constraints.is_a?(Hash)
      query.where constraints
      query
    end
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.