Hibernate注释到瞬态集合字段

Question

I would like a collection field to use a query, but I cannot find a way to do it. There is a @Formula annotation, but that doesn't work with collections. You might ask why I just don't use @ManyToMany or similar annotation. The thing is, I have a table (say, called Relationships) with columns similar to this:

ID | ChildType | ChildID | ParentType | ParentID |

Now, the ChildType and ParentType can be one of many classes in my application, therefore I cannot (I don't want to) use @ManyToMany mapping, since it will create another table for each class. What I would like is, to have a collection field called relationships in, say, class A, that would select all rows (relationships) from Relationship table, where ChildID = A.id and ChildType = 'A' . Is that possible?

Update: Looks like I haven't made myself clear enough. Ok, say, I have a class Relationship where ParentType and ChildType are just class names of parent and child as a String:

@Entity
public class Relationship {
    @Id
    @GeneratedValue
    private Long id;
    @Enumerated(EnumType.STRING)
    private ParentType parentType;
    private Long parentId;
    @Enumerated(EnumType.STRING)
    private ParentType childType;
    private Long childId;
}

Then I have all kinds of classes that have a field relationships , say:

@Entity
public class A {
    @Id
    @GeneratedValue
    private Long id;
    private Set<Relationship> relationships = new HashSet<Relationship>();
}

@Entity
public class B {
    @Id
    @GeneratedValue
    private Long id;
    private Set<Relationship> relationships = new HashSet<Relationship>();
}

@Entity
public class C {
    @Id
    @GeneratedValue
    private Long id;
    private Set<Relationship> relationships = new HashSet<Relationship>();
}

Now I want Hibernate to query the Relationships table to find the relationships for each class, A , B , and C whenever I get an instance bean of corresponding class. Something like this:

@Query("(select relationship from Relationship relationship where relationship.childId = id and relationship.childType = 'A')")
private Set<Relationship> relationships = new ArrayList<Relationship>();

Answer 1

Considering relation_ship is your Relationship table and above described table is parent_child

       SQLQuery query = session.createSQLQuery(
                  "SELECT r
                   FROM relation_ship r
                          INNER JOIN 
                             parent_child  p
                              ON r.id = p.ChildID  and 
                                 p.ChildType := ChildType").setParameter("ChildType","A");

     List<Relationship> = query.list();

Answer 2

I did a workaround for now, but I would still like to know if there is a way to add an annotation in my Entity class instead.

Workaround is as follows: Add a method in the Relationship's repository interface, that extends JpaRepository .

public List<Relationship> findByChildIdAndChildType(Long childId, 
    String childType);

Then, in every service class for A, B, C entities, add relationship resource, and edit find and findAll or whatever methods by adding code that sets the relationships field.

@Service
@Transactional
public class AService implements IAService {
    @Resource
    private IARepository aRepository;
    @Resource
    IRelationshipRepository relationshipRepository;

    @Override
    public A findOne(Long id) {
    A a = aRepository.findOne(id);
    List<Relationship> relationships = new ArrayList<Relationship>();
    relationships = 
                relationshipRepository.findByChildIdAndChildType(id, 'A');
    a.setRelationships(relationships);
    return a;
    }
    // other fields and methods omitted..
}