hibernate annotation多对多中间表添加其他字段的第三种方法

本示例主要以学生（T_Student）和课程（T_Course）之间的多对多关系，中间表Score（分数），学生表和课程表是多对多关系，另外为他们的关系添加额外的字段---分数：

T_Student类如下：

package server.com.upc.test;

import java.util.HashMap;

import java.util.HashSet;

import java.util.Map;

import java.util.Set;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.JoinTable;

import javax.persistence.ManyToMany;

import javax.persistence.MapKey;

@Entity

public class T_Student {

private int id;

private String name;

private Map<String,T_Crouse> course=new HashMap<String,T_Crouse>();

/*

* 或者

* private Set<T_Crouse> course=new HashSet<T_Crouse>();

*

* */

@Id

@GeneratedValue

public int getId() {

return id;

}

public void setId(int id) {

this.id = id;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

/*

* 或者

* @ManyToMany

@JoinTable(

name="score",

joinColumns=@JoinColumn(name="student_id"),

inverseJoinColumns=@JoinColumn(name="course_id")

)

*

*/

@ManyToMany

@MapKey(name="id")

@JoinTable(

name="score",

joinColumns=@JoinColumn(name="student_id"),

inverseJoinColumns=@JoinColumn(name="course_id")

)

public Map<String, T_Crouse> getCourse() {

return course;

}

public void setCourse(Map<String, T_Crouse> course) {

this.course = course;

}

}

T_course类：

package server.com.upc.test;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

@Entity

public class T_Crouse {

private int id;

private String name;

@Id

@GeneratedValue

public int getId() {

return id;

}

public void setId(int id) {

this.id = id;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

}

中间表Score也写成实体类：

package server.com.upc.test;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.ManyToOne;

@Entity

@Table(name="score")

public class T_Score {

private int id;

private int scrores;

private T_Student student;

private T_Crouse course;

@Id

@GeneratedValue

public int getId() {

return id;

}

public int getScrores() {

return scrores;

}

public void setScrores(int scrores) {

this.scrores = scrores;

}

public void setId(int id) {

this.id = id;

}

@ManyToOne

@JoinColumn(name="student_id")

public T_Student getStudent() {

return student;

}

public void setStudent(T_Student student) {

this.student = student;

}

@ManyToOne

@JoinColumn(name="course_id")

public T_Crouse getCourse() {

return course;

}

public void setCourse(T_Crouse course) {

this.course = course;

}

}

注意的是中间表中的导航关系manytomany @JoinColumn(name="course_id")；@JoinColumn(name="course_id")中声明的course_id，student_id和T_student表中声明的要一致,不然会产生其他的字段--再就是中间表的@Table(name="score")score名字和T_Student中的 @JoinTable(

name="score",要一样！！！

建立好之后就会生成中间表含有字段id，student_id,course_id，和score四个字段（然后hibernate生成的主键是（student_id,coure_id））虽然你在T_Score表中声明了自己的id。。。。这是值得注意的地方！