jpa多对多映射案例.docVIP

jpa多对多映射案例 学生和老师就是多对多的关系。一个学生有多个老师，一个老师教多个学生。多对多映射采取中间表连接的映射策略，建立的中间表将分别引入两边的主键作为外键。jpa 对于中间表的元数据提供了可配置的方式，用户可以自定义中间表的表名，列名。 下面就以学生和老师为例介绍多对多映射关系的实例开发 Student实体类 复制代码 package com.ljq.entity; import java.util.HashSet; import java.util.Set; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.ManyToMany; @SuppressWarnings(serial) @Entity public class Student implements java.io.Serializable { /** 学生ID **/ private Integer studentid; /** 学生姓名 **/ private String name; private SetTeacher teachers=new HashSetTeacher(); public Student() { super(); } public Student(String name) { super(); = name; } @Id @GeneratedValue public Integer getStudentid() { return studentid; } public void setStudentid(Integer studentid) { this.studentid = studentid; } @Column(nullable=false,length=32) public String getName() { return name; } public void setName(String name) { = name; } //@ManyToMany注释表示Student是多对多关系的一边，mappedBy属性定义了Student为双向关系的维护端 //Teacher表是关系的维护者，owner side，有主导权，它有个外键指向Student表。 @ManyToMany(mappedBy = students) public SetTeacher getTeachers() { return teachers; } public void setTeachers(SetTeacher teachers) { this.teachers = teachers; } } 复制代码 Teacher实体类 复制代码 package com.ljq.entity; import java.util.HashSet; import java.util.Set; import javax.persistence.CascadeType; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.FetchType; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.JoinColumn; import javax.persistence.JoinTable; import javax.persistence.ManyToMany; @SuppressWarnings(serial) @Entity public class Teacher implements java.io.Serializable { /** 教师ID **/ private Intege