Hibernate通過many-to-one元素的一對一對映

在hibernate中我們可以通過兩種方式來執行一對一對映：

• 通過many-to-one元素標籤
• 通過one-to-one元素標籤

在這裡，我們將通過多對一的many-to-one元素進行一對一的對映。 在這種情況下，在主表中建立外來鍵。

在這個例子中，一個員工只能有一個地址，一個地址只能屬於一個員工。 在這裡使用雙向關聯。 我們來看看持久化類。

一對一對映範例

建立一個名稱為：onetoonemappingforeign的java專案，其專案檔案目錄結構如下 -

1)一對一對映的持久類

有兩個持久化類Employee.java和Address.java。Employee類包含Address類參照，反之亦然(Address類包含Employee類參照)。下面我們來看看它們的程式碼實現。

檔案：Employee.java

package com.yiibai;

public class Employee {
    private int employeeId;
    private String name, email;

    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;
    }

}

檔案：Address.java

package com.yiibai;

public class Address {
    private int addressId;
    private String addressLine1, city, state, country;
    private int pincode;
    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)持久化類對映檔案

兩個對映檔案是employee.hbm.xml和address.hbm.xml。 在employee.hbm.xml對映檔案中，many-to-one元素標籤使用unique =「true」屬性進行一對一對映。

檔案：employee.hbm.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-mapping PUBLIC
          "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
          "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class name="com.yiibai.Employee" table="emp_2110">
        <id name="employeeId">
            <generator class="increment"></generator>
        </id>
        <property name="name"></property>
        <property name="email"></property>

        <many-to-one name="address" unique="true" cascade="all"></many-to-one>
    </class>

</hibernate-mapping>

檔案：address.hbm.xml
這是Address類的簡單對映檔案。

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-mapping PUBLIC
          "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
          "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class name="com.yiibai.Address" table="address_2110">
        <id name="addressId">
            <generator class="increment"></generator>
        </id>
        <property name="addressLine1"></property>
        <property name="city"></property>
        <property name="state"></property>
        <property name="country"></property>

    </class>

</hibernate-mapping>

3)組態檔案

此檔案包含有關資料庫和對映檔案的資訊。

檔案：hibernate.cfg.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
          "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
          "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<!-- Generated by MyEclipse Hibernate Tools. -->
<hibernate-configuration>

    <session-factory>
        <property name="hbm2ddl.auto">update</property>

        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/test</property>
        <property name="connection.username">root</property>
        <property name="connection.password">123456</property>
        <property name="dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>
        <property name="show_sql">true</property>

        <mapping resource="employee.hbm.xml" />
        <mapping resource="address.hbm.xml" />
    </session-factory>

</hibernate-configuration>

4)儲存和獲取資料的使用者類

檔案：MainTest.java 的程式碼如下 -

package com.yiibai;

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

public class MainTest {
    public static void main(String[] args) {
        // 在5.1.0版本匯總，hibernate則採用如下新方式獲取：
        // 1. 組態型別安全的準服務註冊類，這是當前應用的單例物件，不作修改，所以宣告為final
        // 在configure("cfg/hibernate.cfg.xml")方法中，如果不指定資源路徑，預設在類路徑下尋找名為hibernate.cfg.xml的檔案
        final StandardServiceRegistry registry = new StandardServiceRegistryBuilder()
                .configure("hibernate.cfg.xml").build();
        // 2. 根據服務註冊類建立一個後設資料資源集，同時構建後設資料並生成應用一般唯一的的session工廠
        SessionFactory sessionFactory = new MetadataSources(registry)
                .buildMetadata().buildSessionFactory();

        /**** 上面是組態準備，下面開始我們的資料庫操作 ******/
        Session session = sessionFactory.openSession();// 從對談工廠獲取一個session
        // creating transaction object
        Transaction t = session.beginTransaction();

        Employee e1 = new Employee();
        e1.setName("Max Su");
        e1.setEmail("[email protected]");

        Address address1 = new Address();
        address1.setAddressLine1("1688, RenMin Road");
        address1.setCity("Haikou");
        address1.setState("Hainan");
        address1.setCountry("China");
        address1.setPincode(201301);

        e1.setAddress(address1);
        address1.setEmployee(e1);

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

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

檔案：FetchTest.java 的程式碼如下 -

package com.yiibai;

import java.util.Iterator;
import java.util.List;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;

public class FetchTest {
    public static void main(String[] args) {
        // 在5.1.0版本匯總，hibernate則採用如下新方式獲取：
        // 1. 組態型別安全的準服務註冊類，這是當前應用的單例物件，不作修改，所以宣告為final
        // 在configure("cfg/hibernate.cfg.xml")方法中，如果不指定資源路徑，預設在類路徑下尋找名為hibernate.cfg.xml的檔案
        final StandardServiceRegistry registry = new StandardServiceRegistryBuilder()
                .configure("hibernate.cfg.xml").build();
        // 2. 根據服務註冊類建立一個後設資料資源集，同時構建後設資料並生成應用一般唯一的的session工廠
        SessionFactory sessionFactory = new MetadataSources(registry)
                .buildMetadata().buildSessionFactory();

        /**** 上面是組態準備，下面開始我們的資料庫操作 ******/
        Session session = sessionFactory.openSession();// 從對談工廠獲取一個session

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

        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());
        }

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

執行測試

首先執行MainTest.java類，得到輸出結果如下 -

log4j:WARN No appenders could be found for logger (org.jboss.logging).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Mon Mar 27 23:24:53 CST 2017 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
Hibernate: create table address_2110 (addressId integer not null, addressLine1 varchar(255), city varchar(255), state varchar(255), country varchar(255), primary key (addressId)) engine=InnoDB
Hibernate: create table emp_2110 (employeeId integer not null, name varchar(255), email varchar(255), address integer, primary key (employeeId)) engine=InnoDB
Hibernate: alter table emp_2110 drop index UK_o59xt2yukiefdxhv7bx8u0o3a
Hibernate: alter table emp_2110 add constraint UK_o59xt2yukiefdxhv7bx8u0o3a unique (address)
Hibernate: alter table emp_2110 add constraint FKplaygd7gpfedy290hg81wi1ba foreign key (address) references address_2110 (addressId)
Hibernate: select max(employeeId) from emp_2110
Hibernate: select max(addressId) from address_2110
Hibernate: insert into address_2110 (addressLine1, city, state, country, addressId) values (?, ?, ?, ?, ?)
Hibernate: insert into emp_2110 (name, email, address, employeeId) values (?, ?, ?, ?)
success