@OneToMany 一对多 通过表之间的链接

https://blog.csdn.net/qq_38157516/article/details/80146547

一对多

一个人对多张卡，但是一张卡只能对应一个人，典型的一对多关系，下面就用OneToMany来自动生成sql语句

首先建表s_person和s_card表

s_card表

然后在创建一张表关联两张表的关系s_person_card,P_ID为s_person的id,C_ID为s_card的id

建Person.java实体类

@Entity
@Table(name="s_person")
public class Person {

@GeneratedValue(generator = "uuid2")
@GenericGenerator(name = "uuid2", strategy = "uuid2")
@Id
private String id;
private String username;
private String age;

//JoinTable的name是中间表的名字
@OneToMany(fetch=FetchType.EAGER)
@JoinTable(name="s_person_card",joinColumns={@JoinColumn(name="p_id")}
,inverseJoinColumns={@JoinColumn(name="c_id")})
private List<Cards> cards;

public List<Cards> getCards() {
return cards;
}
public void setCards(List<Cards> cards) {
this.cards = cards;
}

public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getAge() {
return age;
}
public void setAge(String age) {
this.age = age;
}

然后是cards表

@Entity
@Table(name="s_card")
public class Cards {
private String id;
private String num;

@GeneratedValue(generator = "uuid2")
@GenericGenerator(name = "uuid2", strategy = "uuid2")
@Id
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getNum() {
return num;
}
public void setNum(String num) {
this.num = num;
}

}
新建接口

public interface PersonRepository extends JpaRepository<Person, String>{

Person findById(String id);

}
测试

@RequestMapping("/person")
@ResponseBody
public Person person(){
Person person=personRepository.findById("12323423");
List<Cards> cards = person.getCards();
for (Cards card : cards) {
System.out.println(card.getId());
System.out.println(card.getNum());
}
return person;
}

结果正常打印，发了两条sql语句，没有手动写sql

只是测试的onetomany，有点复杂，如果在cards类中添加用manytoone就不用创建中间表
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原文链接：https://blog.csdn.net/qq_38157516/article/details/80146547