Hibernate Student_Course_Score设计
示例：
设计代码，实现在数据库中建student表、course表、和score表，展现三者关系
student表：id、name
course表：id、name
score表：id、score、student_id、course_id
三张表的关联关系如下：
设计思路：
1.首先创建Student实体类和Course实体类
会自动创建中间表，通过@JoinTable注解，设置中间表名为“score”，属性名分别为“student_id”和“course_id”
@ManyToMany @JoinTable(name="score", joinColumns={@JoinColumn(name="student_id")}, inverseJoinColumns={@JoinColumn(name="course_id")})
2.创建实体类Score
private int id;
private int score;
private Student student;
private Course course;
根据步骤1中创建的中间表，通过@Table注解设置表名为“score”，
通过@ManyToOne注解设置属性名分别为“student_id”和“course_id”
3.Junit测试类
@Test public void test() { new SchemaExport(new Configuration().configure()).create(true, true); }
具体实现代码如下：
1.Student类
@Entity
public class Student {
private int id;
private String name;
private Set<Course> courses = new HashSet<Course>();
@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;
}
@ManyToMany
@JoinTable(name="score", //中间表名
joinColumns={@JoinColumn(name="student_id")}, //属性名
inverseJoinColumns={@JoinColumn(name="course_id")}) //属性名
public Set<Course> getCourses() {
return courses;
}
public void setCourses(Set<Course> courses) {
this.courses = courses;
}
}
2.Course类
@Entity
public class Course {
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;
}
}
3.Score类
@Entity
@Table(name="score") //对应中间表名
public class Score {
private int id;
private int score;
private Student student;
private Course course;
@Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public int getScore() {
return score;
}
public void setScore(int score) {
this.score = score;
}
@ManyToOne
@JoinColumn(name="student_id") //对应属性名
public Student getStudent() {
return student;
}
public void setStudent(Student student) {
this.student = student;
}
@ManyToOne()
@JoinColumn(name="course_id") //对应属性名
public Course getCourse() {
return course;
}
public void setCourse(Course course) {
this.course = course;
}
}
4.存储一条数据
@Test
public void testsave() {
Session session = sf.getCurrentSession();
session.beginTransaction();
Student s = new Student();
s.setName("lisi");
Course c = new Course();
c.setName("c++");
Score score = new Score();
score.setStudent(s);
score.setCourse(c);
// score.setScore(90); //若不设置，默认为0
session.save(s);
session.save(c);
session.save(score);
session.getTransaction().commit();
}
注意：
create table score (id integer not null, score integer not null, course_id integer, student_id integer not null auto_increment, primary key (student_id, course_id)) 运行程序，会发现通过程序自动建的score表是有问题的。 我们想要的是，id为主键，且自增 而结果是，student_id和course_id为联合主键，且student_id自增 这是hibernate自身的bug，所以应该手动去数据库中，修改表的结构