[英]JPA OneToOne bidirectional .
I have two entity classes that are in @OneToOne relation.我有两个实体类在 @OneToOne 关系中。 The example code are as follow:
示例代码如下:
public class A {
@Id
private int id;
private String name;
@JoinColumn(name = "B_ID", referencedColumnName = "id")
@OneToOne(cascade=CascadeType.ALL)
private B b;
//setters and getters
}
public class B {
@Id
private int id;
private String name;
@OneToOne(mappedBy="b")
private A a;
//setter and getters
}
my question here is "Can I use setA(A a) method in class B. I mean like this. .我的问题是“我可以在 class B 中使用 setA(A a) 方法吗?我的意思是这样......
em.getTransaction().begin();
A aa = new A();
aa.setId(1);
aa.setName("JJ");
em.persist(aa);
B bb = new B();
bb.setId(1);
bb.setName("CC");
bb.setA(aa);
em.persist(bb);
em.getTransaction().commit();
When I tried like this, the foreign_key field in table A (B_ID) was saved as null.当我这样尝试时,表A(B_ID)中的foreign_key字段被保存为null。
Please help me.请帮我。
Here , you have specified mappedBy
in class B above private A a;
在这里,你已经在
private A a;
上面的B类中指定了mappedBy
private A a;
. 。 In a bidirectional relationship ,
mappedBy
means that I am not the owner. 在双向关系中,
mappedBy
意味着我不是所有者。 So It means that A is the owner of the relationship. 所以这意味着A是这段关系的所有者。
In table of A , you will have a foreignkey for table of B. As A is the owner, A is suppose to cascade operations to B. Ideally you should try a.setB()
and then persist a. 在A表中,你将有一个B表的外键。由于A是所有者,A假设将操作级联到B.理想情况下你应该尝试
a.setB()
然后持久化a。
Try below: 试试以下:
em.getTransaction().begin();
//first create B.
B bb = new B();
bb.setId(1);
bb.setName("CC");
em.persist(bb);
//create A with B set in it.
A aa = new A();
aa.setId(1);
aa.setName("JJ");
aa.setB(bb);
em.persist(aa);
em.getTransaction().commit();
Or 要么
em.getTransaction().begin();
//first create B.
B bb = new B();
bb.setId(1);
bb.setName("CC");
// no need to persist bb.
//create A with B set in it.
A aa = new A();
aa.setId(1);
aa.setName("JJ");
aa.setB(bb);
em.persist(aa); // because of cascade all , when you persist A ,
// B will also be persisted.
em.getTransaction().commit();
Use @Cascade({CascadeType.SAVE_UPDATE}) to cascade changes 使用@Cascade({CascadeType.SAVE_UPDATE})级联更改
public class B {
@Id
private int id;
private String name;
@OneToOne(mappedBy="b")
@Cascade({CascadeType.SAVE_UPDATE})
private A a;
//setter and getters
}
you need to add aa.setB(bb) before em.persist(bb) 你需要在em.persist(bb)之前添加aa.setB(bb)
em.getTransaction().begin();
A aa = new A();
aa.setId(1);
aa.setName("JJ");
em.persist(aa);
B bb = new B();
bb.setId(1);
bb.setName("CC");
aa.setB(bb);//this line should be added
bb.setA(aa);
em.persist(bb);
em.getTransaction().commit();
I had also the same problem.我也有同样的问题。 A class had already Setter Method for class B. My Problem was solved with setter in class B. In Class B i put method setter like this.
A class 已经有 class B 的 Setter Method
public void setA(A a){
this.a=a;
a.setB(this);
}
. .
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