Handling Nested DTO Mappings with Spring Boot and JPA in Microservices
I've been struggling with this for a few days now and could really use some help. While refactoring a microservice that interacts with a complex domain model, I’ve come across challenges with mapping nested DTOs effectively using Spring Boot and JPA. Here’s the situation: We have a `User` entity that contains a list of `Address` entities, and I need to convert this structure into a DTO for API responses. The DTO for the user looks like this: ```java public class UserDTO { private Long id; private String name; private List<AddressDTO> addresses; // Getters and Setters } ``` With the AddressDTO structured similarly: ```java public class AddressDTO { private String street; private String city; // Getters and Setters } ``` My initial approach involved using `ModelMapper`, but I’ve run into issues with nested mappings not being handled correctly. The mapping configuration I set up looked like this: ```java ModelMapper modelMapper = new ModelMapper(); modelMapper.typeMap(User.class, UserDTO.class).addMappings(mapper -> { mapper.map(User::getAddresses, UserDTO::setAddresses); }); ``` Unfortunately, this results in `null` for the addresses in the UserDTO. I’ve tried utilizing a custom converter as well, but even that didn’t propagate the data as expected. Furthermore, configuring the `EntityGraph` in JPA for eager fetching leads to performance hits when loading users with numerous addresses. The current implementation also raises concerns about N+1 query problems. To address this, I attempted to use a `JOIN FETCH` in my repository method: ```java @Query("SELECT u FROM User u JOIN FETCH u.addresses WHERE u.id = :id") User findUserWithAddresses(@Param("id") Long id); ``` However, I’m unsure of the best practices regarding DTO projections versus entities and the implications on performance. Any guidance on configuring nested mappings correctly or optimizing performance while still getting the desired DTO structure would be invaluable. Have any of you wrestled with similar challenges? What strategies did you find effective? I'm working on a CLI tool that needs to handle this. Any ideas what could be causing this?