学生, 课程,分数的设计.
a)使用联合主键@EmbeddedId
使用Serializable接口
b)不适用联合主键
联合主键:
3张表,
student: id, name
course: id , name
score:studentid, courseid, score. (两个id就是联合ID)
不使用联合主键的话:
student:id, name
course: id, name
score: id,name, student, course
score--> student: many to one
course-->student: many to one
student->course: many to many
设计:
1. 实体类(表)
2. 导航 (为了编程方便)
3. 确定编程方式
Student.java:
package com.bjsxt.hibernate;
import java.util.HashSet;
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;
@Entity
public class Student {
private int id;
private String name;
private Set<Course> courses = new HashSet<Course>();
@ManyToMany
@JoinTable(name="score",
joinColumns=@JoinColumn(name="student_id", referencedColumnName="id"),
inverseJoinColumns=@JoinColumn(name="course_id", referencedColumnName="id")
)
public Set<Course> getCourses() {
return courses;
}
public void setCourses(Set<Course> courses) {
this.courses = courses;
}
@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;
}
}
Course.java:
package com.bjsxt.hibernate;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
@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;
}
}
Score.java:
package com.bjsxt.hibernate;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
@Entity
@Table(name="score")
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")
public Student getStudent() {
return student;
}
public void setStudent(Student student) {
this.student = student;
}
@ManyToOne
@JoinColumn(name="course_id")
public Course getCourse() {
return course;
}
public void setCourse(Course course) {
this.course = course;
}
}
hibernate.cfg.xml:
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost/hibernate</property>
<property name="connection.username">root</property>
<property name="connection.password">linda0213</property>
<property name="dialect">org.hibernate.dialect.MySQLDialect</property>
<!--
<property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
<property name="connection.url">jdbc:oracle:thin:@localhost:1521:SXT</property>
<property name="connection.username">scott</property>
<property name="connection.password">tiger</property>
<property name="dialect">org.hibernate.dialect.OracleDialect</property>
-->
<!-- JDBC connection pool (use the built-in) -->
<property name="connection.pool_size">1</property>
<!-- Enable Hibernate's automatic session context management -->
<property name="current_session_context_class">thread</property>
<!-- Disable the second-level cache -->
<property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>
<!-- Echo all executed SQL to stdout -->
<property name="show_sql">true</property>
<property name="format_sql">true</property>
<!-- Drop and re-create the database schema on startup
<property name="hbm2ddl.auto">update</property>
-->
<!--
<mapping resource="com/bjsxt/hibernate/Group.hbm.xml"/>
<mapping resource="com/bjsxt/hibernate/User.hbm.xml"/>
-->
<mapping class="com.bjsxt.hibernate.Student"/>
<mapping class="com.bjsxt.hibernate.Course"/>
<mapping class="com.bjsxt.hibernate.Score"/>
</session-factory>
</hibernate-configuration>
test文件:
package com.bjsxt.hibernate;
import java.util.Map;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;
public class HibernateTreeTest {
private static SessionFactory sessionFactory;
@BeforeClass
public static void beforeClass() {
//new SchemaExport(new AnnotationConfiguration().configure()).create(false, true);
sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
}
@AfterClass
public static void afterClass() {
sessionFactory.close();
}
@Test
public void testSave() {
Student s = new Student();
s.setName("zhangsan");
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();
}
@Test
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();
}
@Test
public void testSchemaExport() {
new SchemaExport(new AnnotationConfiguration().configure()).create(false, true);
}
public static void main(String[] args) {
beforeClass();
}
}
最后生成的score有问题, 变成了联合主键, 所以删除掉score表, 自己建一个:
use hibernate; create table score(id int primary key auto_increment,student_id int references student(id),course_id int references course(id), score int)
然后注释掉beforeclass里的创建表语句再次执行就没问题了.