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Hibernate学习4—关联关系一对多映射

作者:dayu

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package com.cy.model;

public class Class {
    private long id;
    private String name;
    
    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;
    }
    
    
}

View Code

com.cy.model.Student:

package com.cy.model;

public class Student {
    private long id;
    private String name;
    private Class c;
    
    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 Class getC() {
        return c;
    }
    public void setC(Class c) {
        this.c = c;
    }
    
    @Override
    public String toString() {
        return "Student [+ name + "]";
    }
    
    
}

Class.hbm.xml:

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<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.cy.model">
    <class name="Class" table="t_class">
        <id name="id" column="classId">
            <generator class="identity"></generator>
        </id>
        <property name="name" column="className"></property>
    </class>
</hibernate-mapping>

View Code

Student.hbm.xml:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.cy.model">
    <class name="Student" table="t_student">
        <id name="id" column="stuId">
            <generator class="identity"></generator>
        </id>
        <property name="name" column="stuName"></property>
        <!-- 
            属性名是c;
            表的外键的列名是classId,关联类com.cy.model.Class
         -->
        <many-to-one name="c" column="classId" class="com.cy.model.Class"></many-to-one>
    </class>
</hibernate-mapping>

hibernate.cfg.xml:

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<?xml version=‘1.0‘ encoding=‘utf-8‘?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

    <session-factory>

        <!--数据库连接设置 -->
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/hibernate</property>
        <property name="connection.username">root</property>
        <property name="connection.password">root</property>
       
        <!-- 方言 -->
        <property name="dialect">org.hibernate.dialect.MySQL5Dialect</property>
    
        <!-- 控制台显示SQL -->
        <property name="show_sql">true</property>

        <!-- 自动更新表结构 -->
        <property name="hbm2ddl.auto">update</property>
        
        <mapping resource="com/cy/model/Student.hbm.xml"/>
        <mapping resource="com/cy/model/Class.hbm.xml"/>
    </session-factory>

</hibernate-configuration>

View Code

测试程序:

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public class StudentTest {
    public static void main(String[] args) {
        SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
        Session session = sessionFactory.openSession();    
        session.beginTransaction();    
        
        Class c = new Class();
        c.setName("08计本");
        session.save(c);
        
        Student s1 = new Student();
        s1.setName("张三");
        s1.setC(c);
        Student s2 = new Student();
        s2.setName("李四");
        s2.setC(c);
        
        session.save(s1);
        session.save(s2);
        
        session.getTransaction().commit();    
        session.close();    
    }
}

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运行之后可以看到建表情况和数据插入情况:

Class表:

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Student表:

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外键关系:

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数据插入成功;

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二、Junit4 方法详解                                        

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下面是测试代码,验证这一过程:

package com.cy.service;

import org.junit.After;
import org.junit.AfterClass;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;

public class StudentTest2 {

    @BeforeClass
    public static void setUpBeforeClass() throws Exception {
        System.out.println("类初始化前调用...");
    }

    @AfterClass
    public static void tearDownAfterClass() throws Exception {
        System.out.println("类初始化后调用...");
    }

    @Before
    public void setUp() throws Exception {
        System.out.println("测试方法前调用...");
    }

    @After
    public void tearDown() throws Exception {
        System.out.println("测试方法后调用...");
    }

    @Test
    public void test() {
        System.out.println("测试方法...");
    }
    
    
    /*
     *  打印如下:
           类初始化前调用...
        测试方法前调用...
        测试方法...
        测试方法后调用...
        类初始化后调用...
     */
}

三、级联保存更新                                              

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比如新建了Class班级,但是没有保存它,但是新建两个Student,引用这个Class,保存这两个Student,观察:

StudentTest3.java:

package com.cy.service;


import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import com.cy.model.Class;
import com.cy.model.Student;
import com.cy.util.HibernateUtil;

public class StudentTest3 {
    private SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
    private Session session;
    
    @Before
    public void setUp() throws Exception {
        session = sessionFactory.openSession();    
        session.beginTransaction();    
    }

    @After
    public void tearDown() throws Exception {
        session.getTransaction().commit();    
        session.close();    
    }

    @Test
    public void testSaveClassAndStudentWithCascade() {
        Class c = new Class();    //临时对象,还没有被持久化
        c.setName("08计本");
        
        Student s1 = new Student();
        s1.setName("张三");
        s1.setC(c);
        Student s2 = new Student();
        s2.setName("李四");
        s2.setC(c);
        
        session.save(s1);    //(cascade为none) student持久化对象引用了一个临时对象,保存抛出异常,保存失败。
        session.save(s2);
    }

}

运行testSaveClassAndStudentWithCascade,发现保存失败:

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于是我们修改Student.hbm.xml中的配置

<hibernate-mapping package="com.cy.model">
    <class name="Student" table="t_student">
        <id name="id" column="stuId">
            <generator class="identity"></generator>
        </id>
        <property name="name" column="stuName"></property>
        <!-- 
            属性名是c;
            表的外键的列名是classId,关联类com.cy.model.Class
         -->
        <many-to-one name="c" column="classId" class="com.cy.model.Class" cascade="save-update"></many-to-one>
    </class>
</hibernate-mapping>

再次运行testSaveClassAndStudentWithCascade,级联保存成功!!



Hibernate学习4—关联关系一对多映射

原文地址:http://www.cnblogs.com/tenWood/p/7242516.html



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