16hibernate hibernate学生、课程、分数设计案例

最新推荐文章于 2018-02-28 09:58:00 发布

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本文介绍了如何利用联合主键和嵌入式对象实现复杂的数据表映射，通过示例展示了如何在Java中使用Hibernate进行数据库操作，包括对象的保存、加载和关联操作。

1.使用联合主键@Embedded
	a.实现Serializable接口

student:
id
name

course://student和course是ManyToMany
id
name

score:(同时是student和course连接表)
//studentid和courseid不能使用自动生成
studentid//先存student，然后把id拿出来放到score表里
courseid//先存course，然后把id拿出来放到score表里
score


2.不使用联合主键(较方便)
student://和score是OneToMany
id
name

course://和score是OneToMany
id
name

score:
id
studentid
courseid
score

@Entity
public class Student
{
	private int id;
	private String name;
	@ManyToMany
	@JoinTable(name="score",
		joinColumns=@JoinColumn(name="student_id"),
		inverseJoinColumns=@JoinColumn(name="course_id")
		)
	private Set<Course> courses = new HashSet<Course>();
	//hibernate会以此为根据建表
	//会将student_id和course_id设置为联合主键
	//此案例中score表手动创建
}

@Entity
public class Course
{
	private int id;
	private String name;
}

@Entity
@Table(name="score")
public class Score
{
	@Id
	@GeneratedValue
	private int id;
	private int score;
	@ManyToOne
	@JoinColumn(name="student_id")
	private Student student;
	@ManyToOne
	@JoinColumn(name="course_id")
	private Course course;
}

public void testSave(){
	Student s = new Student();
	s.setName("zs");
	Course c = new Course();
	c.setName("java");
	Score score = new Score();
	score.setCourse(c);
	score.setStudent(s);

	Session session = sessionFactory.openSession();
	session.beginTransaction();
	session.save(s);
	session.save(c);
	session.save(score);

	session.getTransaction().commit();
	session.close();
}

public void testLoad(){
	testSave();
	Session session = sessionFactory.openSession();
	session.beginTransaction();

	Student s = (Student)session.load(Student.class,1);
	for(Course c:s.getCourses()){
		System.out.println(c.getName());
	}

	session.getTransaction().commit();
	session.close();
}