JPA选择关联并使用NamedEntityGraph

Question

select user.groups
from User user
where user.id = ?1

@Entity
@NamedEntityGraph(name = User.ENTITY_GRAPH,
    attributeNodes = {
        @NamedAttributeNode(User.Fields.permissions),
        @NamedAttributeNode(value = User.Fields.groups, subgraph = "user-groups-subgraph")
    },
    subgraphs = @NamedSubgraph(
        name = "user-groups-subgraph",
        attributeNodes = {
            @NamedAttributeNode(Group.Fields.permissions)
      }
    ))
public class User {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;
  
  @Enumerated(EnumType.STRING)
  @ElementCollection(targetClass = Permission.class)
  @CollectionTable(name = "USERS_PERMISSIONS", joinColumns = @JoinColumn(name = "uid"))
  private Set<Permission> permissions = EnumSet.of(Permission.ROLE_USER);
  
  @ManyToMany(fetch = LAZY)
  private Set<Group> groups = new HashSet<>();
}


@Entity
@NamedEntityGraph(name = Group.ENTITY_GRAPH,
    attributeNodes = {
        @NamedAttributeNode(value = Group.Fields.permissions)
    })
public class Group {

  @Id
  @GeneratedValue(strategy = GenerationType.SEQUENCE)
  private Long id;
  
  @Enumerated(EnumType.STRING)
  @ElementCollection(targetClass = Permission.class)
  @CollectionTable(
      name = "GROUPS_PERMISSIONS",
      joinColumns = @JoinColumn(name = "gid")
  )
  @NonNull
  private Set<Permission> permissions = EnumSet.noneOf(Permission.class);
}

org.hibernate.QueryException:
  query specified join fetching, but the owner of the fetched association was not present in the select list
  [FromElement{explicit,collection join,fetch join,fetch non-lazy properties,classAlias=user,role=foo.bar.User.permissions,tableName={none},tableAlias=permission3_,origin=null,columns={,className=null}}]

我首先尝试了用户图，但是由于我们要获取组，所以我尝试了组图。同样的例外。

问题是，没有简单的方法向生成的查询添加fetch join，因为我不知道应该加入关联的哪些属性。我必须加载Entitygraph，遍历它和任何子图，并生成正确的join子句。

关于查询生成的更多细节：

// QueryDsl 4.3.x Expressions, where propType=Group.class, entityPath=User, assocProperty=groups
final Path<?> expression = Expressions.path(propType, entityPath, assocProperty);

// user.id = ?1
final BooleanExpression predicate = Expressions.predicate(Ops.EQ, idPath, Expressions.constant(rootId));

// QuerydslJpaPredicateExecutor#createQuery from Spring Data JPA
final JPQLQuery<P> query = createQuery(predicate).select(expression).from(path);

// Add Fetch Graph
((AbstractJPAQuery<?, ?>) query).setHint(GraphSemantic.FETCH.getJpaHintName(), entityManager.getEntityGraph(fetchGraph));

// em is EntityManager
List gs = em
                .createQuery("SELECT u.groups FROM User u WHERE u.id = ?1")
                .setParameter(1, user.getId())
                .setHint(GraphSemantic.FETCH.getJpaHintName(), em.getEntityGraph(Group.ENTITY_GRAPH))
                .getResultList();

queryException：查询指定了连接提取，但是提取的关联的所有者不在选择列表中

Answer 1

因此，这个问题可以归结为一个整体图属性的解析问题：

select user.groups
from User user
where user.id = ?1

用实体图

EntityGraph<Group> eg = em.createEntityGraph(Group.class);
eg.addAttributeNodes(Group.Fields.permissions);

提供一个异常，该异常显示Hibernate试图获取user.permissions而不是group.permissions。这是错误报告。