休眠ManyToOne与OneToOne

问题描述

 我无法看到多对一关系模式与OneToOne关系模式的区别。 @Entity 
 public class Order {
 
 @ManyToOne 
 @JoinColumn（nullable = false）
私有地址; 
  

vs

  @Entity 
 public class Order {
 
 @OneToOne 
 @JoinColumn（nullable = false）
私有地址; 
  

是否有区别？

解决方案

它们在模式上看起来完全一样，但是在Hibernate Layer上有所不同。

如果您尝试类似这样的操作：

 地址address = new Address（）; 
 Order order1 = new Order（）; 
 order1.setAddress（address）; 
 Order order2 = new Order（）; 
 order2.setAddress（address）; 
 save（）; 
  

一切都会好的。但是，保存后如果您尝试获取订单：

  @OneToOne案例：
 org.hibernate.HibernateException：超过发现有一行有给定的标识符：1 
 
 @ManyToOne案例：
 SUCCESS 
  

当然，在这两种情况下，您的Address类应该看起来不同。

I can't see any difference in the schema of a Many-To-One relationship vs a OneToOne relationship:

@Entity
public class Order {

    @ManyToOne
    @JoinColumn(nullable = false)
    private Address address;

vs

@Entity
public class Order {

    @OneToOne
    @JoinColumn(nullable = false)
    private Address address;

Is there any difference?

解决方案

They look exactly the same on schema but there is difference on Hibernate Layer.

If you try something like that:

Address address = new Address();
Order order1 = new Order();
order1.setAddress(address);
Order order2 = new Order();
order2.setAddress(address);
save();

Everything will be OK. But, after save if you try get Order:

@OneToOne case:
org.hibernate.HibernateException: More than one row with the given identifier was found: 1

@ManyToOne case:
SUCCESS

Of course, your Address class should looks different in both cases.

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