如何解决 hibernate n+1 问题 OneToMany 和 ManyToOne

Question

我对 N+1 Hibernate 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<>();

public class CouponType {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;


    @ManyToOne
    private Match match;

    @ManyToOne
    private Coupon coupon;

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<>();

我想避免 hibernate 中的 N+1 问题。 如何在 JPQL 中正确查询？

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)

Answer 1

尝试使用以下查询：

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