title: unable to pass values from multiple parent object for mapping through mapstruct
body: <p>I am mapping a scenario where one object of a parent class need to mapped at child level.Now I am unable to pass that object parameter through mapping method.</p>
  
  <pre><code>Mapper class:
  
  @Mapping(target = "segment", source = "flightSegment")
  @Mapping(target = "PTC", source = "passengerFlight")
  Itinerary mapProductAirToItinerary(ProductAir productAir);
  
  List&lt;PTC&gt; mapPassengerFlightToPTC(List&lt;PassengerFlight&gt; passengerFlight);
  
  @Mapping( target = "code", source = "passengerTypeCode")
  @Mapping( target = "numberOfPassengers", source = "passengerQuantity")
  @Mapping( target = "id", source = ***unknown***)
  PTC createSOAPTCfromODflightProduct(PassengerFlight passengerFlight);
  </code></pre>
  
  <p>In this above mapping ProductAir has a string object called ID which is required to be mapped in the method createSOAPTCfromODflightProduct with the target id. Here I have kept is as unknown as I am unable to pass the value of productAir.id to it through mapPassengerFlightToPTC and createSOAPTCfromODflightProduct mapping method. Is there anyway I can pass the value from parent level to child mapping level?
  The structure of product air is given below, SO I want to map the id ->p0 with the id of PTC object</p>
  
  <pre><code>"@type": "ProductAir",
        "totalDuration": "PT3H54M",
        "id": "p0",
        "FlightSegment": [
          {
            "id": "s1",
            "sequence": 1,
            "Flight": {
              "@type": "Flight",
              "duration": "PT3H54M",
              "carrier": "AA",
              "number": "2793",
              "operatingCarrier": "AA",
              "operatingCarrierName": "American Airlines",
              "equipment": "738",
              "id": "f1",
              "Departure": {
                "@type": "Departure",
                "location": "DEN",
                "date": "2020-07-09",
                "time": "23:40:00"
              },
              "Arrival": {
                "@type": "Arrival",
                "location": "MIA",
                "date": "2020-07-10",
                "time": "05:34:00"
              }
            }
  </code></pre>