jpa entitymanager - map query result into nested dto classes-CodePudding

I'm using jpa EntityManager with hibernate in my java spring application. Suppose I have a user entity like below:

public class User {
    private Long id;
    ...
    
    @ManyToOne
    private Address address
}

And I have Custom user dto object for passing into client:

public class UserDTO {
    private Long id;
    private AddressDTO address;
    ...
}

And I have a UserRepository that exceute normal jpql query with EntityManager and Query.

Note, I need to have custom dto, because my dto has some fields that does not exist in entity and must be calculated in query. Now my question: is there any way with EntityManager that map flat query result into my nested UserDTO? In fact, I need to map result of address in AdressDTO inside UserDto and so on.

Note: I want to use jpql not native sql query.

CodePudding user response：

You can construct DTO right in JPQL. Here is an example.

select new your.package.UserDTO(u.id, a.country, a.city, a.street)
from User u join u.address a
where ...

Such query returns List<UserDTO>.

Of course UserDTO has to have appropriate constructor:

public UserDTO(Long id, String country, String city, String street){
   this.id = id;
   this.address = new AddressDTO(country, city, street);
}

CodePudding user response：

You're on the right way.

You really need to fetch User and then convert it to UserDTO. Don't build DTO within your queries.

For that conversion you need Java Mapper. I prefer MapStruct but there is a plenty of such tools (ModelMapper, Dozer etc).

MapStruct is smart enough to manage nested objects as well.