How to add elements in a many-to-many relationship via Spring's @RepositoryRestResource REST API?

Question

I'm having trouble figuring out exactly how to use the @RepositoryRestResource interface to create many-to-many relationships between two fairly simple entities.

For example, I have a simple parent-child entity relationship like this:

@Entity
public class ParentEntity {
    @Id
    @GeneratedValue
    private Long id;

   @ManyToMany
   private List<ChildEntity> children;
}

@Entity
public class ChildEntity {
    @Id
    @GeneratedValue
    private Long id;

    @ManyToMany(mappedBy="children")
    private List<ParentEntity> parents;
}

My repositories are using the vanilla Spring @RepositoryRestResource HATEOS API:

@RepositoryRestResource(collectionResourceRel = "parents", path = "parents")
public interface ParentRepository extends PagingAndSortingRepository<ParentEntity, Long> {
}

@RepositoryRestResource(collectionResourceRel = "children", path = "children")
public interface ChildRepository extends PagingAndSortingRepository<ChildEntity, Long> {
}

I’ve been successful in using POST to create the individual ParentEntity and ChildEntity but I can’t seem to figure out how to PUT/PATCH the relationships between the two using the built-in interface.

It seems like I should be able to use a PUT to send JSON to something like http://localhost:8080/api/parents/1/children, but so far I'm not finding a structure that works.

Answer 1

I found an answer here: How to update reference object in Spring-data rest?

By using "Content-Type: text/uri-list" instead of JSON, it is possible to "add" a resource to the collection with a PUT and pass in the URI. You can remove the resource with a DELETE.

After some digging, I discovered that the Spring documentation does describe this: http://docs.spring.io/spring-data/rest/docs/2.2.0.RELEASE/reference/html/#repository-resources.association-resource.