Spring boot) Spring Data JPA로 CRUD 구현, 게시판 M:N 구현

@RestController
@RequestMapping("/jpa")
public class UserJpaController {
    @Autowired
    private UserRepository userRepository;

}

@Data
@NoArgsConstructor
@Table(name = "User_list")
@Entity
public class User {

    @Id
    private Integer id;
    private String name;
    private Date joinDate;
    private String password;
    private String ssn;
}

@Repository
public interface UserRepository extends JpaRepository<User, Integer> {

}

public class UserJpaController {
	...
    @GetMapping("/users")
    public List<User> retrieveAllUsers(){
        return userRepository.findAll();
    }
}

@RestController
@RequestMapping("/jpa")
public class UserJpaController {
    ...
    @GetMapping("/users/{id}")
    public User retrieveUser(@PathVariable int id){
        Optional<User> user = userRepository.findById(id);

        return user.get();
    }
}

@RestController
@RequestMapping("/jpa")
public class UserJpaController {
    ...
    @GetMapping("/users/{id}")
    public EntityModel<User> retrieveUser(@PathVariable int id){
        Optional<User> user = userRepository.findById(id);

        if(!user.isPresent()){
            throw new UserNotFoundException(String.format("User ID [%s} not found", id));
        }

        EntityModel<User> model = new EntityModel<>(user.get());
        WebMvcLinkBuilder linkTo = linkTo(methodOn(this.getClass()).retrieveAllUsers());
        model.add(linkTo.withRel("all-user"));

        return model;
    }
}

@RestController
@RequestMapping("/jpa")
public class UserJpaController {
    ...
    @DeleteMapping("/users/{id}")
    public void deleteUser(@PathVariable int id){
        userRepository.deleteById(id);
    }
}

@RestController
@RequestMapping("/jpa")
public class UserJpaController {
    ...
    @PostMapping("/users")
    public ResponseEntity<User> createUser(@Valid @RequestBody User user){
        User savedUser = userRepository.save(user);

        URI location = ServletUriComponentsBuilder.fromCurrentRequest()
                .path("/{id}")
                .buildAndExpand(savedUser.getId())
                .toUri();

        return ResponseEntity.created(location).build();
    }
}

@Entity
@Data
@AllArgsConstructor
@NoArgsConstructor
public class UserPost {
    @Id
    @GeneratedValue
    private Integer id;

    private String description;

    @ManyToOne(fetch = FetchType.LAZY)
    @JsonIgnore
    private User user;

}

public class User {
    ...
    @OneToMany(mappedBy = "user")
    private List<UserPost> posts;
}

@RestController
@RequestMapping("/jpa")
public class UserJpaController {
    ...
    @GetMapping("/users/{id}/posts")
    public List<UserPost> retrieveAllPostsByUser(@PathVariable int id){
        Optional<User> user = userRepository.findById(id);

        if(!user.isPresent()){
            throw new UserNotFoundException(String.format("User ID [%s} not found", id));
        }

        return user.get().getPosts();
    }
}

insert into user_post values(1001, 'jeonghoon first post', 1);
insert into user_post values(1002, 'jeonghoon second post', 1);

@Repository
public interface UserPostRepository extends JpaRepository<UserPost, Integer> {
}

@RestController
@RequestMapping("/jpa")
public class UserJpaController {
	...
    @Autowired
    private UserPostRepository userPostRepository;
	...
    @PostMapping("/users/{id}/posts")
    public ResponseEntity<UserPost> createUserPost(@PathVariable int id, @RequestBody UserPost userPost){
        //사용자를 먼저 검색함. Get 메서드에서 긁어왔다.
        Optional<User> user = userRepository.findById(id);
        if(!user.isPresent()){
            throw new UserNotFoundException(String.format("User ID [%s} not found", id));
        }
        userPost.setUser(user.get());

        //검색으로 사용자를 찾으면 savedUserPost에 넘겨준다. Post메서드에서 긁어왔다.
        UserPost savedUserPost = userPostRepository.save(userPost);

        URI location = ServletUriComponentsBuilder.fromCurrentRequest()
                .path("/{id}")
                .buildAndExpand(savedUserPost.getId())
                .toUri();

        return ResponseEntity.created(location).build();
    }
}