Hibernate实战——有连接表的N-1关联

清疚 2021-07-24 13:49 348阅读 0赞

**一 配置文件**

<?xml version="1.0" encoding="GBK"?>
    
    <!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>
               
               <property  name="connection.driver_class">com.mysql.jdbc.Driver</property>
               
               <property  name="connection.url">jdbc:mysql://localhost/hibernate</property>
               
               <property name="connection.username">root</property>
               
               <property name="connection.password">32147</property>
               
               <property  name="hibernate.c3p0.max_size">20</property>
               
               <property name="hibernate.c3p0.min_size">1</property>
               
               <property  name="hibernate.c3p0.timeout">5000</property>
               
               <property  name="hibernate.c3p0.max_statements">100</property>
               <property  name="hibernate.c3p0.idle_test_period">3000</property>
               <property  name="hibernate.c3p0.acquire_increment">2</property>
               <property  name="hibernate.c3p0.validate">true</property>
               
               <property  name="dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>
               
               <property name="hbm2ddl.auto">update</property>
               
               <property name="show_sql">true</property>
               
               <property name="hibernate.format_sql">true</property>
               
               <mapping class="org.crazyit.app.domain.Person"/>
               <mapping class="org.crazyit.app.domain.Address"/>
         </session-factory>
    </hibernate-configuration>

**二 PO**

1 Person

package org.crazyit.app.domain;
    
    import java.util.*;
    
    import javax.persistence.*;
    
    @Entity
    @Table(name="person_inf")
    public class Person
    {
        // 标识属性
        @Id @Column(name="person_id")
        @GeneratedValue(strategy=GenerationType.IDENTITY)
        private Integer id;
        private String name;
        private int age;
        // 定义该Person实体关联的Address实体
        @ManyToOne(targetEntity=Address.class)
        // 显式使用@JoinTable映射连接表
        @JoinTable(name="person_address", // 指定连接表的表名为person_address
            // 指定连接表中person_id外键列，参照到当前实体对应表的主键列
            joinColumns=@JoinColumn(name="person_id"
                , referencedColumnName="person_id", unique=true),
            // 指定连接表中address_id外键列，参照到当前实体的关联实体对应表的主键列
            inverseJoinColumns=@JoinColumn(name="address_id"
                , referencedColumnName="address_id")
        )
        private Address address;
    
        // id的setter和getter方法
        public void setId(Integer id)
        {
            this.id = id;
        }
        public Integer getId()
        {
            return this.id;
        }
    
        // name的setter和getter方法
        public void setName(String name)
        {
            this.name = name;
        }
        public String getName()
        {
            return this.name;
        }
    
        // age的setter和getter方法
        public void setAge(int age)
        {
            this.age = age;
        }
        public int getAge()
        {
            return this.age;
        }
    
        // address的setter和getter方法
        public void setAddress(Address address)
        {
            this.address = address;
        }
        public Address getAddress()
        {
            return this.address;
        }
    }

2 Address

package org.crazyit.app.domain;
    
    import java.util.*;
    
    import javax.persistence.*;
    
    @Entity
    @Table(name="address_inf")
    public class Address
    {
        // 标识属性
        @Id @Column(name="address_id")
        @GeneratedValue(strategy=GenerationType.IDENTITY)
        private int addressId;
        // 定义地址详细信息的成员变量
        private String addressDetail;
    
        // 无参数的构造器
        public Address()
        {
        }
        // 初始化全部成员变量的构造器
        public Address(String addressDetail)
        {
            this.addressDetail = addressDetail;
        }
    
        // addressId的setter和getter方法
        public void setAddressId(int addressId)
        {
            this.addressId = addressId;
        }
        public int getAddressId()
        {
            return this.addressId;
        }
    
        // addressDetail的setter和getter方法
        public void setAddressDetail(String addressDetail)
        {
            this.addressDetail = addressDetail;
        }
        public String getAddressDetail()
        {
            return this.addressDetail;
        }
    }

**三 测试**

1 工具类

package lee;
    
    import org.hibernate.*;
    import org.hibernate.cfg.*;
    import org.hibernate.service.*;
    import org.hibernate.boot.registry.*;
    
    public class HibernateUtil
    {
        public static final SessionFactory sessionFactory;
    
        static
        {
            try
            {
                // 使用默认的hibernate.cfg.xml配置文件创建Configuration实例
                Configuration cfg = new Configuration()
                    .configure();
                // 以Configuration实例来创建SessionFactory实例
                ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
                    .applySettings(cfg.getProperties()).build();
                sessionFactory = cfg.buildSessionFactory(serviceRegistry);
            }
            catch (Throwable ex)
            {
                System.err.println("Initial SessionFactory creation failed." + ex);
                throw new ExceptionInInitializerError(ex);
            }
        }
    
        // ThreadLocal可以隔离多个线程的数据共享，因此不再需要对线程同步
        public static final ThreadLocal<Session> session
            = new ThreadLocal<Session>();
    
        public static Session currentSession()
            throws HibernateException
        {
            Session s = session.get();
            // 如果该线程还没有Session,则创建一个新的Session
            if (s == null)
            {
                s = sessionFactory.openSession();
                // 将获得的Session变量存储在ThreadLocal变量session里
                session.set(s);
            }
            return s;
        }
    
        public static void closeSession()
            throws HibernateException
        {
            Session s = session.get();
            if (s != null)
                s.close();
            session.set(null);
        }
    }

2  测试类

package lee;
    
    import org.hibernate.Transaction;
    import org.hibernate.Session;
    
    import java.util.Date;
    import java.util.Set;
    import java.util.HashSet;
    
    import org.crazyit.app.domain.*;
    
    public class PersonManager
    {
        public static void main(String[] args)
        {
            PersonManager mgr = new PersonManager();
            mgr.testPerson();
            HibernateUtil.sessionFactory.close();
        }
    
        private void testPerson()
        {
            Session session = HibernateUtil.currentSession();
            Transaction tx = session.beginTransaction();
            // 创建一个Person对象
            Person p = new Person();
            // 设置Person的name为crazyit字符串
            p.setName("crazyit");
            p.setAge(21);
            // 创建一个瞬态的Address对象
            Address a = new Address("广州天河");
            // 设置Person和Address之间的关联关系
            p.setAddress(a);
            // 再持久化Address对象
            session.persist(a);
            // 创建一个瞬态的Address对象
            Address a2 = new Address("上海虹口");
            // 设置Person和Address之间的关联关系
            p.setAddress(a2);
            // 由于采用了连接表来维护N-1关联关系，因此不存在主从表关系，
            // 程序可以随意控制先持久化哪个实体。
            // 持久化Address对象
            session.persist(a2);
            // 持久化Person对象
            session.save(p);
            // 持久化Address对象
            session.save(a);
            tx.commit();
            HibernateUtil.closeSession();
        }
    }

**四 测试效果**

Hibernate:
        insert
        into
            address_inf
            (addressDetail)
        values
            (?)
    Hibernate:
        insert
        into
            address_inf
            (addressDetail)
        values
            (?)
    Hibernate:
        insert
        into
            person_inf
            (age, name)
        values
            (?, ?)
    Hibernate:
        insert
        into
            person_address
            (address_id, person_id)
        values
            (?, ?)

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