Java 如何解决hibernate n+1问题

我对N+1休眠有问题。 我有以下实体：

public class Coupon {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "ID")
    private Long id;

    @Builder.Default
    @OneToMany(fetch = FetchType.LAZY,
            targetEntity = CouponType.class,
            cascade = CascadeType.ALL,
            mappedBy = "coupon")
    private List<CouponType> couponTypeList = new ArrayList<>();

我想避免hibernate中的N+1问题。如何在JPQL中正确地编写查询

解决方案：

@Query("select c from Coupon c join fetch c.couponTypeList t join fetch t.match where c.id = ?1") 
Optional<Coupon> getCoupon(Long couponId)

---

尝试使用以下查询：

---

@Queryselect c from优惠券c join fetch c.couponTypeList其中c.id=？1 可选getCouponLong couponId；

---

@查询从优惠券c中选择c join fetch c.couponTypeList t join fetch t.match，其中c.id=？1可选getCouponLong couponId；请注意，在尝试使用“join fetch”进行多个集合获取时，您可能会遇到MultipleBagFetchException。看这个。

public class Match {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "ID")
    private Long id;

    @Builder.Default
    @OneToMany(fetch = FetchType.LAZY,
            targetEntity = CouponType.class,
            mappedBy = "match")
    private List<CouponType> couponTypeList = new ArrayList<>();

@Query("select c from Coupon c join fetch c.couponTypeList t join fetch t.match where c.id = ?1") 
Optional<Coupon> getCoupon(Long couponId)