java - 关系表插入

Question

我有两个实体的多对一关系

@Entity(name = "foo")
public class Foo {

    @Id
    @Column(name = "fooId")
    private Long id;

    @ManyToOne(fetch = FetchType.EAGER,
            targetEntity = Bar.class,
            cascade = { CascadeType.PERSIST, CascadeType.MERGE })
    @JoinColumn(name = "foo")
    private Set<Bar> bars;

    public Foo() {
        bars = new HashSet<>();
    }

    public Set<Bar> getBars() {
        return bars;
    }

    public void setBars(Set<Bar> bars) {
        this.bars = bars;
    }

}

@Entity(name = "bar")
public class Bar {

    @Column(name = "fooId")
    private Foo foo;

    public Bar() {}

}

public class Persist {

    @PersistenceContext(unitName = "myPersistUnit")
    private EntityManager manager;

    public static void main(String[] args) {
        Foo f = new Foo();
        f.getBars().add(new Bar());

        manager.persist(f);
    }
}

但是当我调用 Hibernate persist 方法时，Foo 实体已成功保存，但对于 Bar 实体，我在字段 foo 中遇到了非空违规；

有人可以告诉我我错过了什么吗？

Answer 1

您应该在 Bar Entity 中设置 Foo 实体引用。它会解决你的问题

    Foo f = new Foo();
    Bar bar=new Bar();
    bar.setFoo(f);
    f.getBars().add(bar);
    manager.persist(f);