hibernate多对一单向关联

时间：2021-09-30 16:21:37

关联是类（类的实例）之间的关系，表示有意义和值得关注的连接。

本系列将介绍Hibernate中主要的几种关联映射

Hibernate一对一主键单向关联
Hibernate一对一主键双向关联
Hibernate一对一外键单向关联
Hibernate一对一外键双向关联
Hibernate多对一单向关联
Hibernate多对一双向关联

Hibernate多对多关联

代码都写有注释，主要包括（核心配置文件，实体映射文件，实体类，测试类，数据库）主要操作有增删改查。

本篇主要介绍Hibernate多对一单向关联：

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>
      <!-- 配置数据库连接驱动类 -->
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <!-- 配置数据库连接字符串 -->
        <property name="connection.url"><![CDATA[jdbc:mysql://localhost:3306/test1?useUnicode=true&characterEncoding=utf8]]></property>
        <!-- 配置数据库连接用户名 -->
        <property name="connection.username">root</property>
        <!-- 配置数据库连接密码 -->
        <property name="connection.password">123456</property>
        <!-- 配置数据库方言 -->
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
        <!-- 配置数据库表生成策略 -->
        <!--<property name="hibernate.hbm2ddl.auto">update</property> -->
        <!-- 配置是否打印显示SQL语句 -->
        <property name="show_sql">true</property>
        <!-- 配置是否格式化显示SQL语句 -->
        <property name="format_sql">true</property>
        <!-- 配置hibernate是否自动提交事务 -->
        <!--<property name="hibernate.connection.autocommit">true</property> -->
        <!-- 配置实体类对应的映射文件 -->

        <!-- 多对一单向关联配置 -->
        <mapping resource="com/great/entity1/Product.hbm.xml"></mapping>
        <mapping resource="com/great/entity1/Factory.hbm.xml"></mapping>
    </session-factory>
</hibernate-configuration>

Product.hbm.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>
      <!-- 配置数据库连接驱动类 -->
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <!-- 配置数据库连接字符串 -->
        <property name="connection.url"><![CDATA[jdbc:mysql://localhost:3306/test111?useUnicode=true&characterEncoding=utf8]]></property>
        <!-- 配置数据库连接用户名 -->
        <property name="connection.username">root</property>
        <!-- 配置数据库连接密码 -->
        <property name="connection.password">123456</property>
        <!-- 配置数据库方言 -->
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
        <!-- 配置数据库表生成策略 -->
        <!--<property name="hibernate.hbm2ddl.auto">update</property> -->
        <!-- 配置是否打印显示SQL语句 -->
        <property name="show_sql">true</property>
        <!-- 配置是否格式化显示SQL语句 -->
        <property name="format_sql">true</property>
        <!-- 配置hibernate是否自动提交事务 -->
        <!--<property name="hibernate.connection.autocommit">true</property> -->
        <!-- 配置实体类对应的映射文件 -->

        <!-- 多对一单向关联配置 -->
        <mapping resource="com/great/entity1/Product.hbm.xml"></mapping>
        <mapping resource="com/great/entity1/Factory.hbm.xml"></mapping>

    </session-factory>
</hibernate-configuration>

Factory.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.great.entity1">
    <class name="Factory" table="factory">
        <!-- 配置主键映射关系 -->
        <id name="fId" column="fId" type="int">
            <!-- 配置主键生成策略 -->
            <generator class="identity">
            </generator>
        </id>
        <!-- 配置属性和表字段映射关系 -->
        <property name="fName" column="fName" type="string"></property>
    </class>
</hibernate-mapping>

Product.java

package com.great.entity1;

public class Product {
    // 产品类
    // 产品id
    private int pId;
    // 产品名字
    private String pName;
    // 厂商
    private Factory factory;

    public int getpId() {
        return pId;
    }

    public void setpId(int pId) {
        this.pId = pId;
    }

    public String getpName() {
        return pName;
    }

    public void setpName(String pName) {
        this.pName = pName;
    }

    public Factory getFactory() {
        return factory;
    }

    public void setFactory(Factory factory) {
        this.factory = factory;
    }

}

Factory.java

package com.great.entity1;

public class Factory {
    // 厂商类
    // 厂商id
    private int fId;
    // 厂商名字
    private String fName;

    public int getfId() {
        return fId;
    }

    public void setfId(int fId) {
        this.fId = fId;
    }

    public String getfName() {
        return fName;
    }

    public void setfName(String fName) {
        this.fName = fName;
    }

}

TestManyToOneUnidirectional.java(测试类)

package com.great.test;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;

import com.great.entity1.Factory;
import com.great.entity1.Product;

public class TestManyToOneUnidirectional {
    static Session session;

    // 多对一单向关联
    @BeforeClass
    public static void setUpBeforeClass() throws Exception {
        // 加载hibernate主配置文件
        Configuration cfg = new Configuration().configure();
        // 构建session工厂
        SessionFactory sf = cfg.buildSessionFactory();
        // 打开session
        session = sf.openSession();
    }

    @AfterClass
    public static void tearDownAfterClass() throws Exception {
        // 关闭session，释放资源
        session.close();
    }

    // select1,通过product查询数据
    @Test
    public void testManyToOneSelect1() {
        Product p = (Product) session.get(Product.class, 1);
        System.out.println("产品名字为：" + p.getpName());
        System.out.println("产品厂家为：" + p.getFactory().getfName());
    }

    // insert1数据,只能通过保存product来插入数据
    @Test
    public void testManyToOneSave1() {
        Transaction ts = session.beginTransaction();
        Product p1 = new Product();
        Product p2 = new Product();
        Factory f1 = new Factory();
        f1.setfName("健力宝集团");
        p1.setpName("健力宝");
        p2.setpName("神水");
        p1.setFactory(f1);
        p2.setFactory(f1);
        session.save(p1);
        session.save(p2);
        ts.commit();
    }

    // delete1数据，通过product删除了product.
    @Test
    public void testManyToOneDelete1() {
        Transaction ts = session.beginTransaction();
        Product product = (Product) session.get(Product.class, 8);
        session.delete(product);
        ts.commit();
    }

    // update1,通过product更新数据
    @Test
    public void testManyToOneUpdate1() {
        Transaction ts = session.beginTransaction();
        Product product = (Product) session.get(Product.class, 7);
        product.setpName("神水");
        product.getFactory().setfName("健力宝集团2");
        session.save(product);
        ts.commit();
    }
}

数据库：

product表

三个字段 pId pName fId(外键)

factory表

两个字段  fId fName

注意：在product表的fId上建立外键关系。

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