How to map a List of object present in main object to another object list in mapstruct

Need help with mapstruct mapping new it

How can I map a List of object present in object to another object list.

I have an object

public class ObjectA{

    @Id
    private Long id;

    @OneToMany(mappedBy = "pool", fetch = FetchType.EAGER)
    private List<Pool> pool;
}


public class Pool{

  @Id
  private Long id;

  @OneToOne
  @JoinColumn(name="student")
  private Student student;
}


public class Student {
    @Id
    private Long id;

    @Column(name="number")
    private String number;
}

Now I want to map the the ObjectA to Simple ObjectB

public class ObjectB{

  private Long id;

  private List<String > number;
}

I have tried this

@Mapping(target = "number", source = "pool")
ObjectB map(ObjectA objectA);

Can someone please help and explain how can we do it

Solution

could you please look into this code. I changed the mapper class and added a method for mapping of number of student and number of ObjectB:

@Mapper
public interface ObjectMapper {
    @Mapping(source = "id", target = "id")
    @Mapping(target = "number", expression = "java(mapPoolToStringList(objectA.getPool()))")
    ObjectB mapObjectAtoObjectB(ObjectA objectA);

    default List<String> mapPoolToStringList(List<Pool> poolList) {
        List<String> numberList = new ArrayList<>();
        for (Pool pool : poolList) {
            numberList.add(pool.getStudent().getNumber());
        }
        return numberList;
    }
}

and the main class :

ObjectMapper mapper = Mappers.getMapper(ObjectMapper.class);
    
Student student1 = new Student(1L, "100");
Student student2 = new Student(2L, "200");
Student student3 = new Student(3L, "300");
Student student4 = new Student(4L, "400");

Pool pool1 = new Pool(1L, student1);
Pool pool2 = new Pool(2L, student2);
Pool pool3 = new Pool(3L, student3);
Pool pool4 = new Pool(4L, student4);

List<Pool> poolList = new ArrayList<>();
poolList.add(pool1);
poolList.add(pool2);
poolList.add(pool3);
poolList.add(pool4);

ObjectA objectA = new ObjectA();
objectA.setId(1L);
objectA.setPool(poolList);

ObjectB objectB = mapper.mapObjectAtoObjectB(objectA);

you can see that number of student object is in the objectB.