是否可以在 SpringDataJpa @QueryHint 注释中指定 fetchgraph/loadgraph

Question

是否可以在 Spring 数据 Jpa 中使用 @QueryHint 以某种方式指定javax.persistence.fetchgraph或javax.persistence.loadgraph ？

我有一个实体图

@Entity
@NamedEntityGraph(
        name = "shop_with_all_associations",
        includeAllAttributes = true
)
public class Shop {    
    @JoinColumn(name = "shop_id")
    @OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    private List<Member> members = new ArrayList<>();
}

以及repository中对应的方法

@Repository
public interface ShopRepository extends JpaRepository<Shop, Integer> {
    @QueryHints({@QueryHint(name = "javax.persistence.fetchgraph", value = "shop_with_all_associations")})
    List<Shop> getAllWithQueryHintBy();
}

Answer 1

不，这是不可能的。 您可以在调用该方法时检查您的日志并查看下一个警告

o.h.q.internal.AbstractProducedQuery     : The javax.persistence.fetchgraph hint was set, but the value was not an EntityGraph!

在 AbstractProducedQuery class 中，下一个代码部分显示，只有RootGraph的实例可以被视为 EntityGraph。 但是我们的@QueryHint只允许将字符串作为值传递。

else if ( HINT_FETCHGRAPH.equals( hintName ) || HINT_LOADGRAPH.equals( hintName ) ) {
                if ( value instanceof RootGraph ) {
                    applyGraph( (RootGraph) value, GraphSemantic.fromJpaHintName( hintName ) );
                    applyEntityGraphQueryHint( new EntityGraphQueryHint( hintName, (RootGraphImpl) value ) );
                }
                else {
                    MSG_LOGGER.warnf( "The %s hint was set, but the value was not an EntityGraph!", hintName );
                }
                applied = true;
            }