Hibernate教程-Hibernate 多对一关系示例（使用注解）

在多对一映射中，多个属性可以引用同一个属性。

在这个示例中，每个员工只有一个公司地址，一个地址可以属于多个员工。这里我们将使用注解来执行多对一映射。

让我们来看看持久类。

1) 多对一映射的持久类

这里有两个持久类 Employee.java 和 Address.java。Employee 类包含 Address 类的引用，反之亦然。

Employee.java

package cn.javatiku;

import javax.persistence.*;

@Entity
@Table(name="emp107")
public class Employee {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private int employeeId;
    private String name, email;

    @ManyToOne(cascade=CascadeType.ALL)
    private Address address;

    public int getEmployeeId() {
        return employeeId;
    }

    public void setEmployeeId(int employeeId) {
        this.employeeId = employeeId;
    }

    public String getName() {
        return name;
    }

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

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public Address getAddress() {
        return address;
    }

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

Address.java

package cn.javatiku;

import javax.persistence.*;

@Entity
@Table(name="address107")
public class Address {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private int addressId;
    private String addressLine1, city, state, country;
    private int pincode;

    @OneToOne(cascade=CascadeType.ALL)
    private Employee employee;

    public int getAddressId() {
        return addressId;
    }

    public void setAddressId(int addressId) {
        this.addressId = addressId;
    }

    public String getAddressLine1() {
        return addressLine1;
    }

    public void setAddressLine1(String addressLine1) {
        this.addressLine1 = addressLine1;
    }

    public String getCity() {
        return city;
    }

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

    public String getState() {
        return state;
    }

    public void setState(String state) {
        this.state = state;
    }

    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;
    }

    public Employee getEmployee() {
        return employee;
    }

    public void setEmployee(Employee employee) {
        this.employee = employee;
    }
}

2) 在 pom.xml 文件中添加项目信息和配置

打开 pom.xml 文件并点击源代码。现在，在 <dependencies>....</dependencies> 标签之间添加以下依赖项。这些依赖项用于在 Maven 项目中添加 jar 文件。

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>
    <version>5.3.1.Final</version>
</dependency>

<dependency>
    <groupId>com.oracle</groupId>
    <artifactId>ojdbc14</artifactId>
    <version>10.2.0.4.0</version>
</dependency>

3) 配置文件

此文件包含有关数据库和映射文件的信息。

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">create</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 class="cn.javatiku.Address"/>
        <mapping class="cn.javatiku.Employee"/>
    </session-factory>
</hibernate-configuration>

4) 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();

        Employee e1 = new Employee();
        e1.setName("Ravi Malik");
        e1.setEmail("ravi@gmail.com");

        Employee e2 = new Employee();
        e2.setName("Anuj Verma");
        e2.setEmail("anuj@gmail.com");

        Address address1 = new Address();
        address1.setAddressLine1("G-13,Sector 3");
        address1.setCity("Noida");
        address1.setState("UP");
        address1.setCountry("India");
        address1.setPincode(201301);

        e1.setAddress(address1);
        e2.setAddress(address1);

        session.persist(e1);
        session.persist(e2);
        t.commit();

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

输出

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

        Iterator<Employee> itr = list.iterator();
        while (itr.hasNext()) {
            Employee emp = itr.next();
            System.out.println(emp.getEmployeeId() + " " + emp.getName() + " " + emp.getEmail());
            Address address = emp.getAddress();
            System.out.println(address.getAddressLine1() + " " + address.getCity() + " " +
                               address.getState() + " " + address.getCountry() + " " + address.getPincode());
        }

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

输出