HiberNate学习-四 映射关系-多对多

HiberNate学习-4 映射关系-多对多
<key column="userid"/>
<many-to-many column="roleid"/>
</set>
table属性值必须和单向关联中的table属性值一致
<key>中column属性值要与单向关联中的<many-to-many>标签中的column属性值一致
在<many-to-many>中的column属性值要与单向关联中<key>标签的column属性值一致

?

一：实体类：

三：测试类：

package com.entity; import java.io.Serializable; 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.JoinTable; import javax.persistence.ManyToMany; import javax.persistence.Table; import javax.persistence.JoinColumn; @Entity@Tablepublicclass Teacher implements Serializable { private Integer teacherid;// 教师ID private String teacherName;// 教师姓名 private Set<Student> students = new HashSet<Student>();// 对应的学生集合 public Teacher() { } public Teacher(String teacherName) { this.teacherName = teacherName; } @Id @GeneratedValue public Integer getTeacherid() { return teacherid; } publicvoid setTeacherid(Integer teacherid) { this.teacherid = teacherid; } @Column(nullable = false, length = 32) public String getTeacherName() { return teacherName; } publicvoid setTeacherName(String teacherName) { this.teacherName = teacherName; } /* * @ManyToMany 注释表示Teacher 是多对多关系的一端。 * @JoinTable 描述了多对多关系的数据表关系，name属性指定中间表名称。 * joinColumns 定义中间表与Teacher 表的外键关系，中间表Teacher_Student的Teacher_ID 列是Teacher 表的主键列对应的外键列。 * inverseJoinColumns 属性定义了中间表与另外一端(Student)的外键关系。 */ @ManyToMany(cascade = CascadeType.PERSIST, fetch = FetchType.LAZY) @JoinTable(name = "Teacher_Student", joinColumns ={@JoinColumn(name = "teacher_ID", referencedColumnName = "teacherid") }, inverseJoinColumns = { @JoinColumn(name = "student_ID", referencedColumnName = "studentid") }) public Set<Student> getStudents() { return students; } publicvoid setStudents(Set<Student> students) { this.students = students; } publicvoid addStudent(Student student) { if (!this.students.contains(student)) {//检测在该散列表中某些键是否映射到指定值,value 查找的值。如果某些键映射到该散列表中的值为true，否则false this.students.add(student); } } publicvoid removeStudent(Student student) { this.students.remove(student); } }