Hibernate Fetch不再是Join的子类型

Question

I'm using Hibernate 5.2.10 with dynamic criteria and find out that Fetch is not longer assignable to Join.

In the next example, I need to fetch group data in the same query, but I also need to use the group's field for sorting or restriction.

CriteriaBuilder cb = session.getCriteriaBuilder();
CriteriaQuery<GroupAssignment> query = cb.createQuery(GroupAssignment.class);

Root<GroupAssignment> root = query.from(GroupAssignment.class);
SingularAttributeJoin<GroupAssignment, Group> groupFetch = (SingularAttributeJoin<GroupAssignment, Group>) root.fetch(GroupAssignment_.group, JoinType.LEFT);
query.orderBy(cb.asc(groupFetch.get(Group_.title)));

I have manually cast Fetch to the SingularAttributeJoin and after that, I can use get method for the ordering purpose, but I'm looking for the right way how I can do that without casting manually .

GroupAssignment class:

@Entity()
@Table(name = "group_assignment")
public class GroupAssignment {
  @Id
  @Column(name = "group_assignment_id")
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Integer id;

  @ManyToOne
  @JoinColumn(name = "group_id", nullable = false)
  private Group group;

  //other fields, getters and setters
}

GroupAssignment_ class:

@Generated(value = "org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor")
@StaticMetamodel(GroupAssignment.class)
public abstract class GroupAssignment_ {
  public static volatile SingularAttribute<GroupAssignment, Integer> id;
  public static volatile SingularAttribute<GroupAssignment, Group> group;
}

Group class:

@Entity()
@Table(name = "navigation_group")
public class Group {
  @Id
  @Column(name = "group_id")
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Integer id;

  @Column(name = "title")
  private String title;

  //other fields, getters and setters
}

Group_ class:

@Generated(value = "org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor")
@StaticMetamodel(Group.class)
public abstract class Group_ {
  public static volatile SingularAttribute<Group, Integer> id;
  public static volatile SingularAttribute<Group, String> title;
}

Answer 1

我认为javax.persistence.criteria.FetchParent可以解决您的问题：

FetchParent<GroupAssignment, Group> groupFetch = root.fetch(GroupAssignment_.group, JoinType.LEFT);

Answer 2

It appears that correct way would be next:

query.orderBy(cb.asc(root.get(GroupAssignment_.group).get(Group_.title)));

So using multiple call to .get method you can go as deep as needed.