Implementing a GET service to retrieve all Posts of a User

To implement a GET service that retrieves all posts of a user in a Spring Boot application, you can follow these steps:

1. Create a Post Repository:
   If you haven’t already, create a repository for the Post entity by extending JpaRepository<Post, Long>.
2. Create a Service:
   Create a service class that will handle retrieving posts for a user. Inject the PostRepository and UserRepository as needed.

@Service
public class PostService {

    @Autowired
    private PostRepository postRepository;

    @Autowired
    private UserRepository userRepository;

    public List<Post> getAllPostsByUserId(Long userId) {
        Optional<User> user = userRepository.findById(userId);
        if (user.isPresent()) {
            return postRepository.findByUser(user.get());
        } else {
            throw new UserNotFoundException("User not found with ID: " + userId);
        }
    }
}

3. Create a Controller:
   Create a controller class to handle the REST endpoint for getting all posts of a user. Inject the PostService.

@RestController
@RequestMapping("/users/{userId}/posts")
public class PostController {

    @Autowired
    private PostService postService;

    @GetMapping
    public List<Post> getAllPostsByUserId(@PathVariable Long userId) {
        return postService.getAllPostsByUserId(userId);
    }
}

4. Use the Endpoint:
   You can now access the endpoint using a URL like /users/{userId}/posts to retrieve all posts of a specific user.

In this setup, the getAllPostsByUserId method in the PostService queries the database to find the user by their ID. If the user exists, it then retrieves all posts associated with that user using the findByUser method provided by Spring Data JPA’s query derivation mechanism. If the user is not found, it throws a UserNotFoundException.

The PostController uses the PostService to fetch posts for the requested user and returns them as a list in the response.

Remember to handle imports and error handling properly, and make sure that your database tables are properly set up with the relationships defined in the User and Post entities.