Hibernate

Question

我有一个 ManyToMany table，我想进行这样的查询：

"select e.manytomany.fieldName from Entity e"

我不能 select ManyToMany table 的字段，唯一的可能性是 select table（如 "select e.manytomany from Entity e"）给我一个 Set<>.

有什么方法可以让我进行这样的查询吗？

Answer 1

据我所知，您想完成一个连接条件。

类甲乙：

public class A {

    @Id
    private String id;

    @ManyToMany
    @JoinTable(name="a_b", joinColumns={@JoinColumn(name="a_id")}, inverseJoinColumns={@JoinColumn(name="b_id")})
    private Set<B> b;

    private String field;
}

public class B {

    @Id
    private String id;

    @ManyToMany(mappedBy = "b")
    private Set<A> a;
}

查询：

TypedQuery<String> query = em.createQuery("SELECT a.field FROM A a JOIN B b ON a MEMBER OF b.a AND b = :b", String.class);
query.setParameter("b", someBInstance);

这导致 List<String> 的 "someBInstance.a.field"

Hibernate - 从 ManyToMany 关系访问字段

Hibernate - Accessing fields from a ManyToMany relation

orm

many-to-many

jpql