hibernate中的一对多双向关联

hibernate中的一对多双向关联
上一篇文章​​hibernate中的一对多单向关联介绍了单向关联的实现
上篇博文已经说明了双向关联是彼此把对方设为关联属性，彼此都可以加载和访问对方

一方实体（Country.java）

package com.hibernate.beans;

import java.util.HashSet;
import java.util.Set;

public class Country {
    //域属性
    private Integer countryId;
    private String countryName;
    //关联属性
    private Set<City> citys;
    public Country() {
        citys = new HashSet<City>();
    }
    public Country(String countryName) {
        this();
        this.countryName = countryName;
    }

    public Integer getCountryId() {
        return countryId;
    }
    public void setCountryId(Integer countryId) {
        this.countryId = countryId;
    }
    public String getCountryName() {
        return countryName;
    }
    public void setCountryName(String countryName) {
        this.countryName = countryName;
    }
    @Override
    public String toString() {
        return "Country [countryId=" + countryId + ", countryName="
                + countryName +  "]";
    }
    public Set<City> getCitys() {
        return citys;
    }
    public void setCitys(Set<City> citys) {
        this.citys = citys;
    }


}

多方实体（City.java）

package com.hibernate.beans;

public class City {
    //域属性
    private Integer cityId;
    private String cityName;
    //关联属性
    private Country country;
    public City() {
    }

    public City(String cityName) {
        this.cityName = cityName;
    }

    public Integer getCityId() {
        return cityId;
    }

    public void setCityId(Integer cityId) {
        this.cityId = cityId;
    }

    public String getCityName() {
        return cityName;
    }

    public void setCityName(String cityName) {
        this.cityName = cityName;
    }


    @Override
    public String toString() {
        return "City [cityId=" + cityId + ", cityName=" + cityName
                +  "]";
    }

    public Country getCountry() {
        return country;
    }

    public void setCountry(Country country) {
        this.country = country;
    }

}

映射文件（Country.hbm.xml）

<?xml version="1.0" encoding="UTF-8"?>
<!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.hibernate.beans">
     <class name="Country" table="t_country">
        <!-- 域属性的映射 -->
        <id name="countryId" column="t_countryId">
            <!-- 主键生成策略 -->
            <generator class="native"></generator>
        </id>
        <property name="countryName" column="t_countryName"></property>
        <!-- 关联属性的映射 -->
        <set name="citys" cascade="save-update"><!-- save-update级联保存 -->
            <!-- 一方主键对应在多方表的外键名 -->
            <key column="t_countryId"></key>
            <!-- 多方的类型 -->
            <one-to-many class="City"/>
        </set>
     </class>
 </hibernate-mapping>

映射文件（City.hbm.xml）

<?xml version="1.0" encoding="UTF-8"?>
<!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.hibernate.beans">
     <class name="City" table="t_city">
        <!-- 域属性的映射 -->
        <id name="cityId" column="t_cityId">
            <!-- 主键生成策略 -->
            <generator class="native"></generator>
        </id>
        <property name="cityName" column="t_cityName"></property>
        <!-- 关联属性的映射 -->
        <many-to-one name="country" column="t_countryId" class="Country" cascade="save-update"/>
     </class>
 </hibernate-mapping>

测试类（当1方维护关联关系时）

package com.hibernate.test;


import org.hibernate.Session;
import org.junit.Test;

import com.hibernate.beans.Capital;
import com.hibernate.beans.City;
import com.hibernate.beans.Country;
import com.hibernate.beans.Course;
import com.hibernate.beans.Student;
import com.hibernate.utils.HbnUtils;

public class TestAssociation {
    @Test
    public void test() {
        // 获取连接
        Session session = HbnUtils.getSession();
        try {
            // 开启事务
            session.beginTransaction();


            Country country = new Country("CN");
            City city = new City("武汉");
            City city1 = new City("长沙");

            country.getCitys().add(city);
            country.getCitys().add(city1);


            // 一方维护关联关系
            session.save(country);
            // 提交事务
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            // 回滚
            session.getTransaction().rollback();
        }
    }
}

测试类（当多方维护关联关系时）

package com.hibernate.test;


import org.hibernate.Session;
import org.junit.Test;

import com.hibernate.beans.Capital;
import com.hibernate.beans.City;
import com.hibernate.beans.Country;
import com.hibernate.beans.Course;
import com.hibernate.beans.Student;
import com.hibernate.utils.HbnUtils;

public class TestAssociation {
    @Test
    public void test() {
        // 获取连接
        Session session = HbnUtils.getSession();
        try {
            // 开启事务
            session.beginTransaction();


            Country country = new Country("CN");
            City city = new City("武汉");
            City city1 = new City("长沙");

            city.setCountry(country);
            city1.setCountry(country);

            // 多方维护关联关系
            session.save(city);
            session.save(city1);
            // 提交事务
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            // 回滚
            session.getTransaction().rollback();
        }
    }
}

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