Hibernate教程-双向关联

双向关联允许我们从双方获取依赖对象的详细信息。在这种情况下，我们在两个类中都有对方的引用。

我们以 Employee 和 Address 为例，如果 Employee 类有一个 Address 的引用，并且 Address 有一个 Employee 的引用。此外，如果在映射文件中为这些类应用了一对一或一对多关系，则称为双向关联。

访问我们的一对一和一对多映射页面以了解更多信息。

示例：双向关联的持久类

Employee.java

package cn.javatiku;

import javax.persistence.*;

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

    @OneToOne(mappedBy="employee", 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="address")
public class Address {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private int addressId;
    private String addressLine1, city, state, country;
    private int pincode;

    @OneToOne
    @JoinColumn(name="employee_id")
    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;
    }
}

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 class="cn.javatiku.Employee"/>
        <mapping class="cn.javatiku.Address"/>
    </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();

        Employee e1 = new Employee();
        e1.setName("Ravi Malik");
        e1.setEmail("ravi@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);
        address1.setEmployee(e1);

        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 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