Hibernate教程-组件映射

在组件映射中，我们将依赖对象映射为一个组件。组件是作为一个值存储的对象，而不是实体引用。这主要用于依赖对象没有主键的情况。它用于组成（HAS-A 关系）的情况，因此被称为组件。让我们看看具有 HAS-A 关系的类。

Address.java

package cn.javatiku;

public class Address {
    private String city, country;
    private int pincode;

    // Getters and setters
    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getCountry() {
        return country;
    }

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

    public int getPincode() {
        return pincode;
    }

    public void setPincode(int pincode) {
        this.pincode = pincode;
    }
}

Employee.java

package cn.javatiku;

public class Employee {
    private int id;
    private String name;
    private Address address; // HAS-A relationship

    // Getters and setters
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Address getAddress() {
        return address;
    }

    public void setAddress(Address address) {
        this.address = address;
    }
}

在这里，address 是一个依赖对象。Hibernate 框架提供了将依赖对象映射为组件的功能。让我们看看如何在映射文件中映射这个依赖对象。

employee.hbm.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 5.3//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-5.3.dtd">

<hibernate-mapping>
    <class name="cn.javatiku.Employee" table="emp177">
        <id name="id">
            <generator class="increment"></generator>
        </id>
        <property name="name"></property>

        <component name="address" class="cn.javatiku.Address">
            <property name="city"></property>
            <property name="country"></property>
            <property name="pincode"></property>
        </component>
    </class>
</hibernate-mapping>

配置文件

hibernate.cfg.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD 5.3//EN"
    "http://hibernate.sourceforge.net/hibernate-configuration-5.3.dtd">

<hibernate-configuration>
    <session-factory>
        <property name="hbm2ddl.auto">update</property>
        <property name="dialect">org.hibernate.dialect.Oracle9Dialect</property>
        <property name="connection.url">jdbc:oracle:thin:@localhost:1521:xe</property>
        <property name="connection.username">system</property>
        <property name="connection.password">jtp</property>
        <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
        <mapping resource="employee.hbm.xml"/>
    </session-factory>
</hibernate-configuration>

存储和获取数据的用户类

Store.java

package cn.javatiku;

import org.hibernate.*;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;

public class Store {
    public static void main(String[] args) {
        StandardServiceRegistry ssr = new StandardServiceRegistryBuilder().configure("hibernate.cfg.xml").build();
        Metadata meta = new MetadataSources(ssr).getMetadataBuilder().build();

        SessionFactory factory = meta.getSessionFactoryBuilder().build();
        Session session = factory.openSession();

        Transaction t = session.beginTransaction();

        Address address1 = new Address();
        address1.setCity("Noida");
        address1.setCountry("India");
        address1.setPincode(201301);

        Employee e1 = new Employee();
        e1.setName("Ravi Malik");
        e1.setAddress(address1);

        session.persist(e1);
        t.commit();
        session.close();
        System.out.println("success");
    }
}

Fetch.java

package cn.javatiku;

import java.util.Iterator;
import java.util.List;
import javax.persistence.TypedQuery;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;

public class Fetch {
    public static void main(String[] args) {
        StandardServiceRegistry ssr = new StandardServiceRegistryBuilder().configure("hibernate.cfg.xml").build();
        Metadata meta = new MetadataSources(ssr).getMetadataBuilder().build();

        SessionFactory factory = meta.getSessionFactoryBuilder().build();
        Session session = factory.openSession();

        TypedQuery<Employee> query = session.createQuery("from Employee e");
        List<Employee> list = query.getResultList();

        Iterator<Employee> itr = list.iterator();
        while (itr.hasNext()) {
            Employee e = itr.next();
            System.out.println(e.getId() + " " + e.getName());
            Address address = e.getAddress();
            System.out.println(address.getCity() + " " + address.getCountry() + " " + address.getPincode());
        }

        session.close();
        System.out.println("success");
    }
}

输出

运行 Store.java 时输出：

success

运行 Fetch.java 时输出：

1 Ravi Malik
Noida India 201301
success