[FIXED] Mapstruct one to many ,fill DTO row by row

Issue

There is the Customer entity which has a one to many relationship to entity Address,so there is a List<Address> addresses=new ArrayList<> in Customer.Entity Address has an Email field.

For instance,Customer holds an Address ArrayList with two elements.To get an email from the first customer you do customer.getAddresses.get(0).getEmail

So for Customer ID =6 there can be 2 Addresses with one email per Address. When building the DTO I just need the Customer Id and the Email.

So in that case I would like two rows in the DTO 6 [email protected] 6 [email protected]

Like doing an SQL query and getting two rows back for the same id.

Is there a way to do that with Mapstruct without doing any sql? Like iterating over a collection?

Solution

I am not sure that i understand what you want. Mapstruct is used for mapping and not applying logic. The case that you describe is something that i would solve eiter with SQL or with onboard java utilities.

My approach looks like this

package mapping;

import lombok.Builder;
import lombok.Data;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class MappingMain {
    public static void main(String[] args) {
        Customer customer = Customer.
                builder()
                .id(1)
                .name("John")
                .adresses(Arrays.asList(                                          
Address.builder().email("[email protected]").street("exampleStreet1").build(),                        
Address.builder().email("[email protected]").street("exampleStreet2").build()))
                .build();

    //single customer
    List<ResultingDTO> resultingDTOS =
            customer.getAdresses()
                    .stream()
                    .map(Address::getEmail)
                    .map(email ->
                            ResultingDTO.builder().email(email).id(customer.getId()).build()
                        )
                    .collect(Collectors.toList());
    System.out.println(resultingDTOS);


    //multiple customer "select" by id
    List<Customer> listOfCustomers = Arrays.asList(customer, Customer.builder().id(33).build());

    List<ResultingDTO> resultList = new ArrayList<>();
    listOfCustomers
            .stream()
            .filter(singleCustomer -> singleCustomer.getId() == 1)
            .forEach(customerWithId_1 -> {
                resultList.addAll(customerWithId_1.getAdresses()
                        .stream()
                        .map(Address::getEmail)
                        .map(email ->
                                ResultingDTO.builder().email(email).id(customer.getId()).build()
                        )
                        .collect(Collectors.toList()));
            });
    System.out.println(resultList);

    }

    @Data
    @Builder
    public static class Customer {
        private int id;
        private String name;
        private List<Address> adresses;
    }

    @Data
    @Builder
    public static class Address {
        private String street;
        private String email;
    }

    @Data
    @Builder
    public static class ResultingDTO {
        private int id;
        private String email;
    }


}

Answered By - GJohannes
Answer Checked By - Mary Flores (JavaFixing Volunteer)