Searching and displaying data based on user queries is a pervasive feature of most software applications such as information systems, web portals, and web APIs. The large volume of data managed by these types of systems, henceforth called query-based systems (QBSs), makes them extremely hard to test due to the difficulty to assess whether the output of a query is correct, the so-called test oracle problem. Metamorphic testing has proved to be a very effective approach to alleviate the oracle problem in QBSs, by exploiting the relations among multiple executions of the QBS under test, so-called metamorphic relations (MRs). However, the identification of MRs mostly remains a manual and creative task, limiting the applicability of the approach. In this paper, we propose a method for the automated generation of MRs in QBSs starting from a lightweight specification of the query parameters of the system. Evaluation results show that hundreds of MRs can be automatically identified in real-world systems like IMDb, SkyScanner, or YouTube in just a few seconds.