Hibernate使用@ManyToMany双向关系导致无限循环

Question

I have two entities in my project with have a many-to-many relation between them. The relation is represented using a helper mapping table in postgres which contains the relevant ID for each entity, pretty standard.

Let's call the table bucket_object_mapping and it has two columns: bucket_id , object_id .

The bucket class:

@Entity
@Table(name = "bucket")
public class Bucket {
   // Some fields omitted here

   @ManyToMany(cascade = {}, fetch = FetchType.LAZY)
   @JoinTable(
      name = "bucket_object_mapping",
      joinColumns = @JoinColumn(name = "bucket_id"),
      inverseJoinColumns = @JoinColumn(name = "object_id")
   )
   private List<Model> models;
}

In the Model class I have no mapping to the Bucket class (no need for that)

When I run this simple query:

SELECT bucket FROM Bucket bucket WHERE bucket.customerId=:customerId

The data is returned fine at first, but then an infinite loop of queries to the Model table starts to run and I'm not sure why. Looks like it's happening when I return the result list through a SpringMVC controller. I do convert the Bucket to a DTO but not the Model (It's just that the Model entity does not have any reference to the Bucket so there's not supposed to be a circular reference problem).

Controller code:

@RequestMapping(value = "", method = RequestMethod.GET)
@ResponseBody
public List<BucketDTO> getAllByCustomer(@RequestParam(value = "customerid") final Long customerId) {
  return bucketService.getAllBucketsForCustomer(customerId);
}

The code in the service:

@Transactional
public List<BucketDTO> getAllBucketsForCustomer(final Long customerId) {
  List<Bucket> buckets = bucketDao.getBucketsForCustomer(customerId);
  List<BucketDTO> result = bucketDtoConverter.toDtoList(buckets);
  return result
}

Answer 1

Turns out the problem was originated in the Model . While Model does not have any reference to Bucket it does have a reference to another object with a @OneToMany annotation (and the referenced object references Model with @ManyToOne ).

I converted everything (Bucket, Model and the 3rd object) to DTOs and now it works. The reason for it to work is because the infinite loop was caused when the jackson lib tried to serialize the result . Because there was a bidirectional reference from the Model object to another object it got stuck in an infinite loop trying to serialize those. By converting to DTO I made sure that only Model holds a reference to the other object so it solves the issue.

You can follow the chat that led to the answer here

Answer 2

I thnik you should delete relation from Model (if you have) or add MappedBy. When you have relation on Model.class and no @MappedBy so you create first record on table bucket_object_mapping for Bucket and second record for Model