Java JPA-具有自定义左连接的规范

我有4个实体：

Parent、Alpha、Omega、Beta

@Audited @Entity @Table(name = "parent")
public class Parent extends AuditEntity  {

    @Id @Column(nullable = false)
    @GeneratedValue ....
    private Long id;

    @OneToMany(mappedBy = "parent", fetch = FetchType.LAZY, cascade = CascadeType.ALL,
            orphanRemoval = true)
    @JsonIgnore
    private Set<Alpha> alphas;
}

/**
*   Alpha connects Parent & Omega by containing their Ids mapping. It uses ParentAlphaId.java as ID class.
*/
@Audited @Entity @Table (name = "alpha")
@IdClass(ParentAlphaId.class)
public class Alpha extends AuditEntity {

    @Id
    @Column(name = "parent_id", nullable = false)
    private Long parentId;

    @Id
    @Column(name = "omega_id", nullable = false)
    private Long omegaId;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "parent_id", referencedColumnName = "id", nullable = false, insertable = false, updatable = false)
    private Parent parent;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "omega_id", referencedColumnName = "id", nullable = false, insertable = false, updatable = false)
    private Omega omega;

}

@Entity @Audited @Table(name = "omega"
public class Omega extends AuditEntity {

    @Id
    @GeneratedValue ....
    private long id;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "beta", nullable = false)
    private Beta beta;

}

@Entity @Audited @Table(name = "beta")
public class Beta extends AuditEntity {

    @Id @Column
    private long id;

    @Column(nullable = false)
    private Integer archived;   // archived can be 0 or 1.
}

其目的是从父级、alpha和omega获取ID，在beta中存档的ID为0

对于beta为1的其他记录，它将报告为null

为此，我在父级存储库中编写了以下规范，即

root

位于

Parent

：

public static Specification<Parent> getParentWithActiveBeta() {
    return (root, query, cb) -> {
        Fetch<Object, Object> alpha = root.fetch("alpha", JoinType.LEFT);
        Fetch<Object, Object> omega = alpha.fetch("omega", JoinType.LEFT);
        Fetch<Object, Object> beta = omega.fetch("beta", JoinType.LEFT);
        beta.on(cb.equal(beta.get("archived"), 0));
        return null;
    };
}

公共静态规范getParentWithActiveBeta（）{
返回（根、查询、cb）->{
Fetch alpha=root.Fetch（“alpha”，JoinType.LEFT）；
Fetch omega=alpha.Fetch（“omega”，JoinType.LEFT）；
Fetch beta=omega.Fetch（“beta”，JoinType.LEFT）；
beta.on（cb.equal（beta.get（“存档”），0））；
返回null；
};
}

SQL查询似乎工作得很好，但当我运行规范时，我会得到归档为1的记录的测试版ID

我原以为它们会变成空的

---

我缺少什么？

您不应该使用

fetch

而是

join

，因为

fetch

会导致JPQL/HQL

join fetch

不支持

谓词上的
。您可以使用如下所示的存储库方法：

@Query("SELECT p.id, a.id, o.id, b.id, b.archived FROM Parent p JOIN p.alphas a JOIN a.omega o JOIN o.beta b ON b.archived = false")
public List<Tuple> findWhatever();

@Query（“选择p.id、a.id、o.id、b.id、b.archived FROM Parent p JOIN p.alphas a JOIN a.omega o JOIN o.beta b ON b.archived=false”）
公共列表findWhatever（）；
您不应该使用
fetch
而是
join
，因为
fetch
会导致JPQL/HQL
join fetch
不支持
上的
谓词。您可以使用如下所示的存储库方法：

@Query("SELECT p.id, a.id, o.id, b.id, b.archived FROM Parent p JOIN p.alphas a JOIN a.omega o JOIN o.beta b ON b.archived = false")
public List<Tuple> findWhatever();

@Query（“选择p.id、a.id、o.id、b.id、b.archived FROM Parent p JOIN p.alphas a JOIN a.omega o JOIN o.beta b ON b.archived=false”）
公共列表findWhatever（）；