MapStruct - Map list of objects in single object

Loren 0
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I am getting a list of objects from 3rd party but it will always contain one object only. So at my end in target I have created it as an object rather than list. That object contains multiple lists inside it just like source object.

This is how I am trying to map a list to an object. ChargeTransaction contain orderInvoice as an object and not a list. For list which are inside ChargeTransaction I have created separate mappers. I dont want to write java code in @afterMapping because then how nested lists will be mapped. The nested lists are of type in both the objects.

@Mapping(target = "orderInvoice", source = "basePaymentRequest.invoice.eventPayload.orderInvoices")
ChargeTransaction createInvoiceCTMapper(PaymentTriggerBaseModel basePaymentRequest, ChargeType chargeType);

Error

java: Can't map property "List<OrderInvoice> basePaymentRequest.invoice.eventPayload.orderInvoices" to "OrderInvoice orderInvoice". Consider to declare/implement a mapping method: "OrderInvoice map(List<OrderInvoice> value)".

I tried

@Mapping(target = "orderInvoice", expression= "java(basePaymentRequest.invoice.eventPayload.orderInvoices.get(0))")

But it gives error in Impl class

 chargeTransaction.setOrderInvoice( basePaymentRequest.invoice.eventPayload.orderInvoices.get(0) );

 java: incompatible types: com.sams.oms.ng.common.models.payment.request.OrderInvoice cannot be converted to com.sams.oms.ng.common.models.payment.cosmos.OrderInvoice
java-11 mapstruct java list
1 Answers

IMHO the best way to solve this problem is to use a @Named paired with @Mapping#qualifiedByName

@Mapper
class Mapper {

  @Mapping(target = "orderInvoice", source ="basePaymentRequest.invoice.eventPayload.orderInvoices", qualifiedByName="firstElement")
  ChargeTransaction createInvoiceCTMapper(PaymentTriggerBaseModel basePaymentRequest, ChargeType chargeType);

  @Named("firstElement")
  OrderInvoice map(List<OrderInvoice> value) {
    if(value == null) return null;
    if(value.isEmpty()) return null;
    return map(value.get(0));
  }

  abstract com.sams.oms.ng.common.models.payment.request.OrderInvoice map(com.sams.oms.ng.common.models.payment.cosmos.OrderInvoice invoice);
}

In this way you are instructed MapStruct to use map(List<>) to convert invoices to a single OrderInvoice and abstract map(OrderInvoice) to let MapStruct autogenerate mapping code.

Code in untested because I haven't limited spare time today,but I hope my example may be useful;if anything is wrong feel free to comment and I will correct code asap.

Luca Basso Ricci0
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