我正在尝试查询具有映射到几个简单子实体的实体列表（ MyOrder s）：每个 MyOrder 恰好与一个 Store ，零个或多个 Transaction 以及最多一个 Tender 相关联 . 生成的SELECT显示正确 - 它从所有四个连接表中检索所有列 - 但之后，为每个 MyOrder 执行另外两个SELECT，一个用于 Transaction ，一个用于 Tender .

我正在使用QueryDSL 4.1.3，Spring Data 1.12，JPA 2.1和Hibernate 5.2 .

在QueryDSL中，我的查询是：

... = new JPAQuery<MyOrder>(entityManager)
    .from(qMyOrder)
    .where(predicates)
    .join(qMyOrder.store).fetchJoin()
    .leftJoin(qMyOrder.transactions).fetchJoin()
    .leftJoin(qMyOrder.tender).fetchJoin()
    .orderBy(qMyOrder.orderId.asc())
    .transform(GroupBy
        .groupBy(qMyOrder.orderId)
        .list(qMyOrder));

执行方式如下：

SELECT myorder0_.ord_id AS col_0_0_,
    myorder0_.ord_id AS col_1_0_,
    store1_.sto_id AS sto_id1_56_1_, -- store's PK
    transactions3_.trn_no AS trn_no1_61_2_, -- transaction's PK
    tender4_.tender_id AS pos_trn_1_48_3_, -- tender's PK
    myorder0_.ord_id AS ord_id1_39_0_,
    myorder0_.app_name AS app_name3_39_0_, -- {app_name, ord_num} is unique
    myorder0_.ord_num AS ord_num8_39_0_,
    myorder0_.sto_id AS sto_id17_39_0_,
    store1_.division_num AS div_nu2_56_1_,
    store1_.store_num AS store_nu29_56_1_,
    transactions3_.trn_cd AS trn_cd18_61_2_,
    tx2myOrder2_.app_name AS app_name3_7_0__, -- join table
    tx2myOrder2_.ord_no AS ord_no6_7_0__,
    tx2myOrder2_.trn_no AS trn_no1_7_0__,
    tender4_.app_name AS app_name2_48_3_,
    tender4_.ord_num AS ord_num5_48_3_,
    tender4_.tender_cd AS tender_cd_7_48_3_,
FROM data.MY_ORDER myorder0_
INNER JOIN data.STORE store1_ ON myorder0_.sto_id=store1_.sto_id
LEFT OUTER JOIN data.TX_to_MY_ORDER tx2myOrder2_
    ON myorder0_.app_name=tx2myOrder2_.app_name
    AND myorder0_.ord_num=tx2myOrder2_.ord_no
LEFT OUTER JOIN data.TRANSACTION transactions3_ ON tx2myOrder2_.trn_no=transactions3_.trn_no
LEFT OUTER JOIN data.TENDER tender4_
    ON myorder0_.app_name=tender4_.app_name
    AND myorder0_.ord_num=tender4_.ord_num
ORDER BY myorder0_.ord_id ASC

这几乎是我所期待的 . （为简洁起见，我删除了大部分数据列，但我需要的是SELECTed . ）

在查询内存中的H2数据库（使用Spring的 @DataJpaTest 注释进行设置）时，执行此查询后，将对 Tender 表进行第二次查询，但不会对 Transaction 进行查询 . 查询MS SQL数据库时，初始查询是相同的，但对 Tender 和 Transaction 都会发生其他查询 . 没有进行额外的调用来加载 Store .

我发现的所有来源都表明 .fetchJoin() 应该足够了（例如Opinionated JPA with Query DSL;从锚点向上滚动几行），如果我删除它们，初始查询只会从MY_ORDER中选择列 . 所以看起来 .fetchJoin() 确实强制生成一次查取所有边表的查询，但由于某种原因额外的信息不是真的很奇怪，我确实看到 Transaction 数据附加在我的H2准单元测试中没有第二个查询（当且仅当我使用.fetchJoin（））但不使用MS SQL时 .

我尝试使用 @Fetch(FetchMode.JOIN) 注释实体映射，但是辅助查询仍然会触发 . 我怀疑可能有一个涉及扩展 CrudRepository<> 的解决方案，但我没有成功，甚至初始查询在那里正确 .

我的主要实体映射，使用Lombok的 @Data 注释，其他字段为了简洁而修剪 . （ Store ， Transaction 和 Tender 都有 @Id 一些简单的数字和字符串字段列映射，没有 @Formula 或 @OneToOne 或其他任何内容 . ）

@Data
@NoArgsConstructor
@Entity
@Immutable
@Table(name = "MY_ORDER", schema = "Data")
public class MyOrder implements Serializable {

@Id
@Column(name = "ORD_ID")
private Integer orderId;

@NonNull
@Column(name = "APP_NAME")
private String appName;
@NonNull
@Column(name = "ORD_NUM")
private String orderNumber;

@ManyToOne
@JoinColumn(name = "STO_ID")
private Store store;

@OneToOne
@JoinColumns({
        @JoinColumn(name = "APP_NAME", referencedColumnName = "APP_NAME", insertable = false, updatable = false),
        @JoinColumn(name = "ORD_NUM", referencedColumnName = "ORD_NUM", insertable = false, updatable = false)})
@org.hibernate.annotations.ForeignKey(name = "none")
private Tender tender;

@OneToMany
@JoinTable(
        name = "TX_to_MY_ORDER", schema = "Data",
        joinColumns = { // note X_to_MY_ORDER.ORD_NO vs. ORD_NUM
                @JoinColumn(name = "APP_NAM", referencedColumnName = "APP_NAM", insertable = false, updatable = false),
                @JoinColumn(name = "ORD_NO", referencedColumnName = "ORD_NUM", insertable = false, updatable = false)},
        inverseJoinColumns = {@JoinColumn(name = "TRN_NO", insertable = false, updatable = false)})
@org.hibernate.annotations.ForeignKey(name = "none")
private Set<Transaction> transactions;

/**
 * Because APP_NAM and ORD_NUM are not foreign keys to TX_TO_MY_ORDER (and they shouldn't be),
 * Hibernate 5.x saves this toString() as the 'owner' key of the transactions collection such that
 * it then appears in the transactions collection's own .toString(). Lombok's default generated
 * toString() includes this.getTransactions().toString(), which causes an infinite recursive loop.
 * @return a string that is unique per order
 */
@Override
public String toString() {
    // use appName + orderNumber since, as they are the columns used in the join, they must (?) have
    // already been set when attaching the transactions - primary key sometimes isn't set yet.
    return this.appName + "\00" + this.orderNumber;
}
}

我的问题是：为什么我得到多余的SELECT，我怎么能不这样做？

java hibernate jpa spring-data querydsl