[FIXED] Getting an error with mapping when using MongoRepository findById

Issue

When I try to use the findById method from MongoRepository with a string passed in, I get an error with the mapper which leads to no results being returned, even though such exists.

Here is my project's structure and files:

Entity Post.java

@Document("posts")
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Post {
    @Id
    private String Id;
    private Integer userId;
    private String content;
    private Integer likes;
    private Integer dislikes;
}

Repository PostRepository.java

public interface PostRepository extends MongoRepository<Post, String> {

}

Service PostService.java

@Service
public class PostService {

    @Autowired
    private PostRepository repository;

    public List<Post> getPosts() {
        return repository.findAll();
    }

    public Post getPostById(String id) {
        return repository.findById(id).orElse(null);
    }

    public Post savePost(Post post) {
        return repository.save(post);
    }

    public void deletePostById(String id) {
        repository.deleteById(id);
    }

}

Controller PostController.java

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

    @Autowired
    private PostService service;

    @Autowired
    private StreamBridge streamBridge;

    @GetMapping("")
    public List<Post> getPosts() {
        return service.getPosts();
    }

    @GetMapping("/{postId}")
    public Post getPostById(@PathVariable String postId) {
        return service.getPostById(postId);
    }

    @PostMapping("/createPost")
    public Post createPost(@RequestBody Post post) {
        streamBridge.send("postCreated-out-0", post.getUserId());
        return service.savePost(post);
    }

    @DeleteMapping("/{postId}")
    public void deletePostById(@PathVariable String postId) {
        service.deletePostById(postId);
    }
}

When I try running either a GET such as localhost:9192/posts/62a76719145e644e5b640327 or a DELETE localhost:9192/posts/62a76719145e644e5b640327, where 62a76719145e644e5b640327 is a correct id associated with a entry in the document in MongoDB I get this error in the console:

[nio-9192-exec-2] o.s.d.mongodb.core.convert.QueryMapper   : Could not map 'Post.id'. Maybe a fragment in 'String' is considered a simple type. Mapper continues with id.

I also tried writing a custom query using the @Query annotation that overwrites the default findById as such:

@Override
@Query("{ 'id' :  ?0}")
Optional<Post> findById(String s);

And I still get the same error. I am using spring-boot-starter-data-mongodb version 2.7.0 and I am running MongoDB locally.

EDIT: Forgot to mention that the same thing happens when using the deleteById method

Solution

i think the problem is in the identifier u named it with capital I replace Id in posts document with id ? give it a try... it will work

Answered By - Ahmed Abd Elnasser
Answer Checked By - David Goodson (JavaFixing Volunteer)