Spring Data JPA: How to fetch all entities of a specific type along with each entity's associated entities? - spring

Question

I have a Post entity
#Entity
public class Post {
#Id
private UUID id;
#NotNull
private String title;
#NotNull
private String content;
#NotNull
private String identifier;
#NotNull
private String category;
#NotNull
#Column(name = "created_at")
private Date createdAt;
#NotNull
#Column(name = "updated_at")
private Date updatedAt;
public Post (){
}
public Post (String title, String content, String category){
this.title = title;
this.content = content;
this.category = category;
}
// rest of the getters and setters
}
And this is my Comment entity:
#Entity
public class Comment {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private UUID id;
#NotNull
private String name;
#NotNull
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer identifier;
#NotNull
private String email;
#NotNull
private String content;
#NotNull
#ManyToOne
#JoinColumn(name = "post_id")
private Post postId;
#NotNull
#Column(name = "created_at")
private Date createdAt;
public Comment() {
}
public Comment(String name, String email, String content){
this.name = name;
this.email = email;
this.content = content;
}
}
And this is my post controller:
#RestController
#RequestMapping("/posts")
public class PostController {
private String getIdentifier(String str){
return String.join("-", str.split(" "));
}
#Autowired
private PostService postService;
#RequestMapping(value = "", method = {GET, HEAD})
public List<Post> getAllPosts(){
return postService.getAllPosts();
}
#RequestMapping(value = "", method = {POST, OPTIONS})
public Post addNewPost(#RequestBody Post post){
post.setId(UUID.randomUUID());
post.setIdentifier(this.getIdentifier(post.getTitle()));
post.setCreatedAt(new Date());
post.setUpdatedAt(new Date());
return postService.savePost(post);
}
#RequestMapping(value = "/{id}", method = {GET, HEAD})
public Post getOnePost(#PathVariable UUID id){
return postService.getOne(id);
}
#RequestMapping(value = "/{id}", method = DELETE)
public void deleteOnePost(#PathVariable UUID id){
postService.deleteOnePost(id);
}
}
My question is how do I fetch all the comments for each individual post, whenever I fetch all the posts?
Sorry, I come from a NoSQL background, so this is a bit daunting at first.

Answer 1

What you need to do is to create a bidirectional #OneToMany association from the Post to Comments:
add a field in Post class
#OneToMany(
mappedBy = "postId",
cascade = CascadeType.ALL
)
private List<Comments> comments = new ArrayList<>();
From now on, when you get Post from the database, Comments will be fetched at the same time.