hibernate 注解入门实例

班级（一）--->学生（多）

package com.xh.hibernate.beans;import javax.persistence.*;/** * Created by root on 17-5-12. */@Entity@Tablepublic class Student {    @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    @Column(name="id",nullable = false,unique = true)    private Long id;    private String name;    @ManyToOne    @JoinColumn(name = "cid")    private Classes classes;    public Long getId() {        return id;    }    public void setId(Long id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public Classes getClasses() {        return classes;    }    public void setClasses(Classes classes) {        this.classes = classes;    }}

package com.xh.hibernate.beans;import javax.persistence.*;import java.util.Set;/** * Created by root on 17-5-12. */@Entity@Tablepublic class Classes {    @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    @Column(name="id",nullable = false,unique = true)    private Long id;    private String name;    @OneToMany(mappedBy = "classes",cascade = {CascadeType.ALL} )    private Set<Student> students;    public Long getId() {        return id;    }    public void setId(Long id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public Set<Student> getStudents() {        return students;    }    public void setStudents(Set<Student> students) {        this.students = students;    }}

hibernate.cfg.xml

<!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="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>        <!--hibernate_first要操作的数据库-->        <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/test</property>        <property name="hibernate.connection.username">root</property>        <property name="hibernate.connection.password"></property>        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>        <property name="hbm2ddl.auto">update</property>        <!--是否在控制台输出操作的sql语句-->        <property name="hibernate.show_sql">true</property>        <mapping class="com.xh.hibernate.beans.Student" ></mapping>        <mapping class="com.xh.hibernate.beans.Classes" ></mapping>    </session-factory></hibernate-configuration>

测试类;

package com.xh.hibernate;import com.xh.hibernate.beans.Classes;import com.xh.hibernate.beans.Student;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.Transaction;import org.hibernate.cfg.Configuration;import org.junit.Test;import java.util.HashSet;import java.util.Set;/** * Unit test for simple App. */public class AppTest {    Configuration configuration = new Configuration().configure("hibernate.cfg.xml");    SessionFactory sessionFactory = configuration.buildSessionFactory();    @Test    public void saveStu() {        Session session = sessionFactory.openSession();        Transaction transation = session.getTransaction();//获得事务        transation.begin();//开启事务        Student student = new Student();        student.setName("s1");        session.save(student);        transation.commit();//提交事务    }    /**     * saveStu():     * MariaDB [test]> select * from Student;     * +----+------+------+     * | id | name | cid  |     * +----+------+------+     * |  1 | s1   | NULL |     * +----+------+------+     */    @Test    public void saveClas() {        Session session = sessionFactory.openSession();        Transaction transation = session.getTransaction();//获得事务        transation.begin();//开启事务        Classes classes = new Classes();        Set c1 = new HashSet();        classes.setName("1b");        Student student1 = new Student();        student1.setName("1b-s1");        Student student2 = new Student();        student2.setName("1b-s2");        c1.add(student1);        c1.add(student2);        //保存Classes之前先要让Student拥有Classes        student1.setClasses(classes);        student2.setClasses(classes);        classes.setStudents(c1);        //session.save(classes);        session.persist(classes);        transation.commit();//提交事务    }    /**    @Test    public void saveClas() {    Session session = sessionFactory.openSession();    Transaction transation = session.getTransaction();//获得事务    transation.begin();//开启事务    Classes classes = new Classes();    Set c1 = new HashSet();    classes.setName("1b");    Student student1 = new Student();    student1.setName("1b-s1");    Student student2 = new Student();    student2.setName("1b-s2");    c1.add(student1);    c1.add(student2);    classes.setStudents(c1);    session.save(classes);    transation.commit();//提交事务    }     *saveClas():     *MariaDB [test]> select * from Student;     +----+-------+------+     | id | name  | cid  |     +----+-------+------+     |  1 | s1    | NULL |     |  2 | 1b-s1 | NULL |     |  3 | 1b-s2 | NULL |     +----+-------+------+     MariaDB [test]> select * from Classes;     +----+------+     | id | name |     +----+------+     |  1 | 1b   |     +----+------+     Student的外键为空，是因为Classes不负责维护关系，好像mappedBy 就意味inverse=true     hibernate默认只能是多的一方维护关系。     所以在保存Classes之前先要让Student拥有Classes。     于是添加：     @Test     public void saveClas() {     Session session = sessionFactory.openSession();     Transaction transation = session.getTransaction();//获得事务     transation.begin();//开启事务     Classes classes = new Classes();     Set c1 = new HashSet();     classes.setName("1b");     Student student1 = new Student();     student1.setName("1b-s1");     Student student2 = new Student();     student2.setName("1b-s2");     c1.add(student1);     c1.add(student2);     //保存Classes之前先要让Student拥有Classes     student1.setClasses(classes);     student2.setClasses(classes);     classes.setStudents(c1);     session.save(classes);     transation.commit();//提交事务     }     MariaDB [test]> select * from Student;     +----+-------+------+     | id | name  | cid  |     +----+-------+------+     |  1 | s1    | NULL |     |  2 | 1b-s1 | NULL |     |  3 | 1b-s2 | NULL |     |  4 | 1b-s1 |    2 |     |  5 | 1b-s2 |    2 |     +----+-------+------+     MariaDB [test]> select * from Classes;     +----+------+     | id | name |     +----+------+     |  1 | 1b   |     |  2 | 1b   |     +----+------+     */    @Test    public void delClasses(){        Session session = sessionFactory.openSession();        Transaction transation = session.getTransaction();//获得事务        transation.begin();//开启事务        //System.out.println(session.get(Classes.class,5L).toString());        Classes classes=(Classes)session.get(Classes.class,7L);        for (Student s:classes.getStudents()){            s.setClasses(null);        }        session.delete(classes);        transation.commit();//提交事务    }    /**     *首先看看数据库     * MariaDB [test]> select * from Classes;     +----+------+     | id | name |     +----+------+     |  5 | 1b   |     +----+------+     1 row in set (0.00 sec)     MariaDB [test]> select * from Student;     +----+-------+------+     | id | name  | cid  |     +----+-------+------+     | 12 | s1    | NULL |     | 13 | 1b-s1 |    5 |     | 14 | 1b-s2 |    5 |     +----+-------+------+    执行后：     MariaDB [test]> select * from Student;     +----+------+------+     | id | name | cid  |     +----+------+------+     | 12 | s1   | NULL |     +----+------+------+     1 row in set (0.00 sec)    说明级联删除了     如果我不想级联删除，希望只删除Classes，Student的cid置空     1、先修改Classes的cascade = {CascadeType.ALL}改为：     cascade = {CascadeType.PERSIST,CascadeType.MERGE,CascadeType.REFRESH}    2、session.save(classes);改为       session.persist(classes);     否则不会级联保存学生     现在的数据库：     MariaDB [test]> select * from Student;     +----+-------+------+     | id | name  | cid  |     +----+-------+------+     | 12 | s1    | NULL |     | 15 | 1b-s1 |    7 |     | 16 | 1b-s2 |    7 |     +----+-------+------+     3 rows in set (0.00 sec)     MariaDB [test]> select * from Classes;     +----+------+     | id | name |     +----+------+     |  6 | 1b   |     |  7 | 1b   |     +----+------+     2 rows in set (0.00 sec)     @Test     public void delClasses(){     Session session = sessionFactory.openSession();     Transaction transation = session.getTransaction();//获得事务     transation.begin();//开启事务     //System.out.println(session.get(Classes.class,5L).toString());     Classes classes=(Classes)session.get(Classes.class,7L);     session.delete(classes);     transation.commit();//提交事务     }     Cannot delete or update a parent row: a foreign key constraint fails (`test`.`Student`, CONSTRAINT `FK_ot8tyy5l6tvxn3xxphmx1efl6` FOREIGN KEY (`cid`) REFERENCES `Classes` (`id`))     at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)     at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)     at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)     at java.lang.reflect.Constructor.newInstance(Constructor.java:423)     at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)     看来不用CascadeType.REMOVE 并非智能的不删除关联对象     好像Hibernate不会自动置空（也许有，但我目前还没有发现），所以要手动：     @Test     public void delClasses(){     Session session = sessionFactory.openSession();     Transaction transation = session.getTransaction();//获得事务     transation.begin();//开启事务     //System.out.println(session.get(Classes.class,5L).toString());     Classes classes=(Classes)session.get(Classes.class,7L);     for (Student s:classes.getStudents()){     s.setClasses(null);     }     session.delete(classes);     transation.commit();//提交事务     }     MariaDB [test]> select * from Student;     +----+-------+------+     | id | name  | cid  |     +----+-------+------+     | 12 | s1    | NULL |     | 15 | 1b-s1 | NULL |     | 16 | 1b-s2 | NULL |     +----+-------+------+     3 rows in set (0.00 sec)     MariaDB [test]> select * from Classes;     +----+------+     | id | name |     +----+------+     |  6 | 1b   |     +----+------+     1 row in set (0.00 sec)     */}