JPA 使用@OneToMany

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