JPA实现“多对多”映射

迈不过友情╰ 2021-07-25 00:28 392阅读 0赞

**一 代码位置**

[https://gitee.com/cakin24/code/tree/master/08/JpaManyToManyDemo][https_gitee.com_cakin24_code_tree_master_08_JpaManyToManyDemo]

**二 关键代码**

1 Student

package com.example.demo.entity;
    
    import lombok.Data;
    import javax.persistence.*;
    import java.util.List;
    import java.util.Set;
    
    @Entity
    @Data
    public class Student {
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private long id;
        private String name;
        @Column(columnDefinition = "enum('male','female')")
        private String sex;
    
        @ManyToMany(fetch=FetchType.LAZY)
        @JoinTable(name="teacher_student",joinColumns={@JoinColumn(name="s_id")},inverseJoinColumns={@JoinColumn(name="t_id")})
        private Set<Teacher> teachers;
    }

2 Teacher

package com.example.demo.entity;
    
    import lombok.Data;
    import javax.persistence.*;
    import java.util.List;
    import java.util.Set;
    
    @Data
    @Entity
    public class Teacher {
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private long id;
        private String name;
        @ManyToMany(fetch=FetchType.LAZY)
        /**
         * Description:
         * 1、关系两边都作为主控；
         * 2、joinColumns中@JoinColumn(name="t_id") 其中t_id为JoinTable 中的外键，由于 Student 和Teacher 的主键都为id 这边就省略referencedColumnName="id"。
         */
         @JoinTable(name="teacher_student",joinColumns={@JoinColumn(name="t_id")},inverseJoinColumns={@JoinColumn(name="s_id")})
        private Set<Student> students;
    }

3 测试代码

package com.example.demo.entity;
    
    import com.example.demo.repository.StudentRepository;
    import com.example.demo.repository.TeacherRepository;
    import org.junit.Test;
    import org.junit.runner.RunWith;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.boot.test.context.SpringBootTest;
    import org.springframework.test.context.junit4.SpringRunner;
    import java.util.HashSet;
    import java.util.Set;
    
    @SpringBootTest
    @RunWith(SpringRunner.class)
    public class ManyToManyTest {
        @Autowired
        private StudentRepository studentRepository;
        @Autowired
        private TeacherRepository teacherRepository;
    
        @Test
        public void add() {
            Set<Teacher> teachers = new HashSet<>();
            Set<Student> students = new HashSet<>();
    
            Student student1 = new Student();
            student1.setName("zhonghua");
            students.add(student1);
            studentRepository.save(student1);
    
            Student student2 = new Student();
            student2.setName("zhiran");
            students.add(student2);
            studentRepository.save(student2);
    
            Teacher teacher1 =new Teacher();
            teacher1.setName("龙老师");
            teacher1.setStudents(students);
            teachers.add(teacher1);
            teacherRepository.save(teacher1);
        }
    }

**三 测试结果**

1 控制台输出

Hibernate: insert into student (name, sex) values (?, ?)
    Hibernate: insert into student (name, sex) values (?, ?)
    Hibernate: insert into teacher (name) values (?)
    Hibernate: insert into teacher_student (t_id, s_id) values (?, ?)
    Hibernate: insert into teacher_student (t_id, s_id) values (?, ?)

2 数据库输出

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70][]

[https_gitee.com_cakin24_code_tree_master_08_JpaManyToManyDemo]: https://gitee.com/cakin24/code/tree/master/08/JpaManyToManyDemo
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70]: /images/20210724/84cdd340e3aa427fb3fbaecdcd53c823.png