使用注解用Hibernate自动创建多对多数据表
之前我们用hibernate连接已经创建的数据表，并避免了直接写SQL语言。
同样，对于多对多的关系映射，我们可以直接在程序中定义这种对象的关系，然后JPA会自动帮助我们创建表和相关关系。
创建项目
- 与之前一样，创建Hibernate项目。
- 需要额外注意，JDK9以上需要添加JPA额外的包才不会报错，具体请参考这里。
- 同时，将Postgres的JAR包加入lib。
设置xml
设置
hibernate.cfg.xml，注意，由于我们对象对应的表在该数据库中不存在，因此要添加自动创建表的设置<?xml version='1.0' encoding='utf-8'?> <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD//EN" "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"> <hibernate-configuration> <session-factory> <property name="connection.driver_class">org.postgresql.Driver</property> <!-- hibernate.connection.url : 连接数据库的地址,路径 --> <property name="hibernate.connection.url">jdbc:postgresql://localhost:5432/stu</property> <property name="hibernate.connection.username">postgres</property> <property name="hibernate.connection.password">xxx</property> <!-- show_sql: 操作数据库时,会 向控制台打印sql语句 --> <property name="show_sql">true</property> <!-- format_sql: 打印sql语句前,会将sql语句先格式化 --> <!--自动创建表--> <property name="hibernate.hbm2ddl.auto">update</property> <!-- Set "true" to show SQL statements --> <property name="hibernate.show_sql">true</property> <!-- mapping class using annotation --> <mapping class="Entity.Student"></mapping> <mapping class="Entity.Teacher"></mapping> <!-- DB schema will be updated if needed --> <!-- <property name="hbm2ddl.auto">update</property> --> </session-factory> </hibernate-configuration>
项目结构
我们以老师和学生多对多的关系举例
学生
package Entity;
import javax.persistence.*;
import java.io.Serializable;
import java.util.Date;
import java.util.Set;
@Entity
//@Table(name = "t_student")
//@SequenceGenerator(name = "SEQ_STUDENT", sequenceName = "SEQ_STUDENT")
public class Student implements Serializable {
private static final long serialVersionUID = 2524659555729848644L;
private Long id;
private String name;
private Date birthday;
private int sex;
private String address;
private Set<Teacher> teacherList;
private Integer a;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id", nullable = false, precision = 22, scale = 0)
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
@Column(name = "name")
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Temporal(TemporalType.DATE)
@Column(name = "birthday")
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
@Column(name = "sex")
public int getSex() {
return sex;
}
public void setSex(int sex) {
this.sex = sex;
}
@Column(name = "address")
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
@ManyToMany(cascade = CascadeType.ALL)
@JoinTable(name = "t_teacher_student",
joinColumns = @JoinColumn(name = "stu_id",referencedColumnName="id"),
inverseJoinColumns = @JoinColumn(name = "teacher_id",referencedColumnName ="id"))
public Set<Teacher> getTeacherList() {
return teacherList;
}
public void setTeacherList(Set<Teacher> teacherList) {
this.teacherList = teacherList;
}
}
老师
package Entity;
import Entity.Student;
import javax.persistence.*;
import java.io.Serializable;
import java.util.Set;
@Entity
//@Table(name = "t_teacher")
//@SequenceGenerator(name = "SEQ_TEACHER", sequenceName = "SEQ_TEACHER")
public class Teacher implements Serializable {
private static final long serialVersionUID = 2297316923535111793L;
private Long id;
private String name;
private int sex;
private Set<Student> studentList;
@Id
// @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQ_TEACHER")
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id", nullable = false, precision = 22, scale = 0)
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
@Column(name = "name")
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Column(name = "sex")
public int getSex() {
return sex;
}
public void setSex(int sex) {
this.sex = sex;
}
@ManyToMany(mappedBy = "teacherList", cascade = CascadeType.ALL)
public Set<Student> getStudentList() {
return studentList;
}
public void setStudentList(Set<Student> studentList) {
this.studentList = studentList;
}
}
Main
import Entity.Student;
import Entity.Teacher;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import java.util.HashSet;
import java.util.Set;
public class Main {
public static void main(final String[] args) throws Exception {
//创建配置对象(读取配置文档)
Configuration config = new Configuration().configure();
//创建会话工厂对象
SessionFactory sessionFactory = config.buildSessionFactory();
//会话对象
Session session = sessionFactory.openSession();
//这是开启Session的操作
session.beginTransaction();
Student s = new Student();
s.setName("小猪");
Teacher t = new Teacher();
t.setName("小李");
Set<Teacher> t_set = new HashSet<Teacher>();
t_set.add(t);
s.setTeacherList(t_set);
session.save(s);
//此处才是真正与数据库交互的语句
session.getTransaction().commit();
session.close();
}
}
运行
运行后，打印SQL语句，发现hibernate帮我们创建了表，并添加了数据
在shell中查看数据：
