hibernate中的一对多双向关联

港控/mmm° 2023-10-17 11:35 104阅读 0赞

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][hibernate]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">
            
            <id name="countryId" column="t_countryId">
                
                <generator class="native"></generator>
            </id>
            <property name="countryName" column="t_countryName"></property>
            
            <set name="citys" cascade="save-update">
                
                <key column="t_countryId"></key>
                
                <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">
            
            <id name="cityId" column="t_cityId">
                
                <generator class="native"></generator>
            </id>
            <property name="cityName" column="t_cityName"></property>
            
            <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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[hibernate]: http://blog.csdn.net/leisure_life/article/details/62043040