Hibernate通過many-to-one元素的一對一映射

在hibernate中我們可以通過兩種方式來執行一對一映射：

通過many-to-one元素標籤
通過one-to-one元素標籤

在這裏，我們將通過多對一的many-to-one元素進行一對一的映射。在這種情況下，在主表中創建外鍵。

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。在這裏使用雙向關聯。我們來看看持久化類。

一對一映射示例

創建一個名稱爲：onetoonemappingforeign的java項目，其項目文件目錄結構如下 -

Hibernate通過many-to-one元素的一對一映射

1)一對一映射的持久類

有兩個持久化類Employee.java和Address.java。Employee類包含Address類引用，反之亦然(Address類包含Employee類引用)。下面我們來看看它們的代碼實現。

文件：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;
}

}

文件：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)持久化類映射文件

兩個映射文件是employee.hbm.xml和address.hbm.xml。在employee.hbm.xml映射文件中，many-to-one元素標籤使用unique =「true」屬性進行一對一映射。

文件：employee.hbm.xml

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

文件：address.hbm.xml
這是Address類的簡單映射文件。

</class>

3)配置文件

此文件包含有關數據庫和映射文件的信息。

文件：hibernate.cfg.xml

<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>

4)存儲和獲取數據的用戶類

文件：MainTest.java 的代碼如下 -

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版本彙總，hibernate則採用如下新方式獲取：
// 1. 配置類型安全的準服務註冊類，這是當前應用的單例對象，不作修改，所以聲明爲final
// 在configure("cfg/hibernate.cfg.xml")方法中，如果不指定資源路徑，默認在類路徑下尋找名爲hibernate.cfg.xml的文件
final StandardServiceRegistry registry = new StandardServiceRegistryBuilder()
.configure("hibernate.cfg.xml").build();
// 2. 根據服務註冊類創建一個元數據資源集，同時構建元數據並生成應用一般唯一的的session工廠
SessionFactory sessionFactory = new MetadataSources(registry)
.buildMetadata().buildSessionFactory();

    /\*\*\*\* 上面是配置準備，下面開始我們的數據庫操作 \*\*\*\*\*\*/
    Session session = sessionFactory.openSession();// 從會話工廠獲取一個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");
}

}

文件：FetchTest.java 的代碼如下 -

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版本彙總，hibernate則採用如下新方式獲取：
// 1. 配置類型安全的準服務註冊類，這是當前應用的單例對象，不作修改，所以聲明爲final
// 在configure("cfg/hibernate.cfg.xml")方法中，如果不指定資源路徑，默認在類路徑下尋找名爲hibernate.cfg.xml的文件
final StandardServiceRegistry registry = new StandardServiceRegistryBuilder()
.configure("hibernate.cfg.xml").build();
// 2. 根據服務註冊類創建一個元數據資源集，同時構建元數據並生成應用一般唯一的的session工廠
SessionFactory sessionFactory = new MetadataSources(registry)
.buildMetadata().buildSessionFactory();

    /\*\*\*\* 上面是配置準備，下面開始我們的數據庫操作 \*\*\*\*\*\*/
    Session session = sessionFactory.openSession();// 從會話工廠獲取一個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");
}

}

運行測試

首先運行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

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Hibernate通過many-to-one元素的一對一映射

一對一映射示例

1)一對一映射的持久類

2)持久化類映射文件

3)配置文件

4)存儲和獲取數據的用戶類

運行測試