Hibernate实战——基于复合主键的关联关系

￡神魔★判官ぃ 2021-07-25 00:53 454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**

Person

package org.crazyit.app.domain;
    
    import java.util.*;
    
    import javax.persistence.*;
    
    @Entity
    @Table(name="person_inf")
    public class Person
        implements java.io.Serializable
    {
        // 定义first成员变量，作为标识属性的成员
        @Id
        private String first;
        // 定义last成员变量，作为标识属性的成员
        @Id
        private String last;
        private int age;
        // 记录该Person实体关联的所有Address实体
        @OneToMany(targetEntity=Address.class, mappedBy="person"
            , cascade=CascadeType.ALL)
        private Set<Address> addresses
            = new HashSet<>();
    
        // first的setter和getter方法
        public void setFirst(String first)
        {
            this.first = first;
        }
        public String getFirst()
        {
            return this.first;
        }
    
        // last的setter和getter方法
        public void setLast(String last)
        {
            this.last = last;
        }
        public String getLast()
        {
            return this.last;
        }
    
        // age的setter和getter方法
        public void setAge(int age)
        {
            this.age = age;
        }
        public int getAge()
        {
            return this.age;
        }
    
        // addresses的setter和getter方法
        public void setAddresses(Set<Address> addresses)
        {
            this.addresses = addresses;
        }
        public Set<Address> getAddresses()
        {
            return this.addresses;
        }
    
        // 重写equals()方法，根据first、last进行判断
        public boolean equals(Object obj)
        {
            if (this == obj)
            {
                return true;
            }
            if (obj != null && obj.getClass() == Person.class)
            {
                Person target = (Person)obj;
                return target.getFirst().equals(this.first)
                    && target.getLast().equals(this.last);
            }
            return false;
        }
    
        // 重写hashCode()方法，根据first、last计算hashCode值
        public int hashCode()
        {
            return getFirst().hashCode() * 31
                + getLast().hashCode();
        }
    }

Address

package org.crazyit.app.domain;
    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;
         // 定义代表地址详细信息的成员变量
         private String addressDetail;
         // 记录该Address实体关联的Person实体
         @ManyToOne(targetEntity=Person.class)
         // 使用@JoinColumns包含多个@JoinColumn定义外键列
         @JoinColumns({
               // 由于主表使用了复合主键（有多个主键列）
               // 因此需要使用多个@JoinColumn定义外键列来参照person_inf表的多个主键列
               @JoinColumn(name="person_first"
                    , referencedColumnName="first" ,  nullable=false),
               @JoinColumn(name="person_last"
                    , referencedColumnName="last" , nullable=false)
         })
         private Person person;
         // 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;
         }
         // person的setter和getter方法
         public void setPerson(Person person)
         {
               this.person = person;
         }
         public Person getPerson()
         {
               return this.person;
         }
    }

**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.*;
    import org.crazyit.app.domain.*;
    
    public class PersonManager
    {
        public static void main(String[] args)
        {
            PersonManager mgr = new PersonManager();
            mgr.createAndStorePerson();
            HibernateUtil.sessionFactory.close();
        }
        private void createAndStorePerson()
        {
            Session session = HibernateUtil.currentSession();
            Transaction tx = session.beginTransaction();
            // 创建Person对象
            Person person = new Person();
            person.setAge(29);
            // 为复合主键的两个成员设置值
            person.setFirst("crazyit.org");
            person.setLast("疯狂Java联盟");
            Address a1 = new Address("广州天河");
            a1.setPerson(person);
            Address a2 = new Address("上海虹口");
            a2.setPerson(person);
            // 先保存主表实体
            session.save(person);
            // 再保存从表实体
            session.save(a1);
            session.save(a2);
            tx.commit();
            HibernateUtil.closeSession();
        }
    }

**四 测试**

Hibernate:
        insert
        into
            person_inf
            (age, last, first)
        values
            (?, ?, ?)
    Hibernate:
        insert
        into
            address_inf
            (addressDetail, person_last, person_first)
        values
            (?, ?, ?)
    Hibernate:
        insert
        into
            address_inf
            (addressDetail, person_last, person_first)
        values
            (?, ?, ?)

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