hibernate one-to-many many-to-one 雙向註解

環境：

Hibernate 3.3.1 
Maven 3.0.4 
MySQL 5.5.13 
Myeclipse 8.6.1

建表語句：

DROP TABLE IF EXISTS `t_company`;
CREATE TABLE `t_company` (
  `companyId` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `companyName` varchar(30) NOT NULL,
  PRIMARY KEY (`companyId`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=gb2312;

INSERT INTO `t_company` VALUES ('1', 'Sun');
INSERT INTO `t_company` VALUES ('2', 'Apache');

DROP TABLE IF EXISTS `t_employee`;
CREATE TABLE `t_employee` (
  `employeeId` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `employeeName` varchar(15) NOT NULL,
  `cid` int(10) unsigned NOT NULL,
  PRIMARY KEY (`employeeId`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=gb2312;

INSERT INTO `t_employee` VALUES ('1', 'Tom', '1');
INSERT INTO `t_employee` VALUES ('2', 'Summ', '1');
INSERT INTO `t_employee` VALUES ('3', 'Cat', '2');
INSERT INTO `t_employee` VALUES ('4', 'Vinylon', '1');
INSERT INTO `t_employee` VALUES ('5', 'Dog', '2');

目錄結構：

Employee.java

package com.fancy.po;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
/**
 * -----------------------------------------
 * @文件: Employee.java
 * @做者: fancy
 * @郵箱: fancyzero@yeah.net
 * @時間: 2012-6-10
 * @描述: 實體類
 * -----------------------------------------
 */
/**
 * 下面只說@ManyToOne,如需瞭解其餘註解,
 * 能夠參考上一篇：http://www.cnblogs.com/fancyzero/archive/2012/06/10/hibernate-one-to-one-annotation.html
 */
@Entity
@Table(name = "t_employee")
public class Employee {

    private Integer employeeId;
    private String  employeeName;
    private Company company;
    
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public Integer getEmployeeId() {
        return employeeId;
    }
    /**
     * @ManyToOne：多對一,cascade：級聯,請參考上一篇
      * fetch = FetchType.LAZY,延遲加載策略,若是不想延遲加載能夠用FetchType.EAGER
     */
    @ManyToOne(cascade = {CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REFRESH},fetch = FetchType.LAZY)
    @JoinColumn(name = "cid")
    public Company getCompany() {
        return company;
    }
    public String getEmployeeName() {
        return employeeName;
    }
    public void setEmployeeId(Integer employeeId) {
        this.employeeId = employeeId;
    }
    public void setEmployeeName(String employeeName) {
        this.employeeName = employeeName;
    }
    public void setCompany(Company company) {
        this.company = company;
    }
}

Company.java

package com.fancy.po;

import java.util.Set;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
/**
 * -----------------------------------------
 * @文件: Company.java
 * @做者: fancy
 * @郵箱: fancyzero@yeah.net
 * @時間: 2012-6-10
 * @描述: 實體類
 * -----------------------------------------
 */
/**
 * 下面只說@OneToMany,如需瞭解其餘註解,
 * 能夠參考上一篇：http://www.cnblogs.com/fancyzero/archive/2012/06/10/hibernate-one-to-one-annotation.html
 */
@Entity
@Table(name = "t_company")
public class Company {

    private Integer companyId;
    private String  companyName;
    private Set<Employee> employees;
    
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public Integer getCompanyId() {
        return companyId;
    }
    /**
     * @OneToMany 與 OneToOne類似的也用mappedBy,參考了Employee
     * 能夠參考上一篇
     */
    @OneToMany(mappedBy = "company")
    public Set<Employee> getEmployees() {
        return employees;
    }
    public String getCompanyName() {
        return companyName;
    }
    public void setCompanyId(Integer companyId) {
        this.companyId = companyId;
    }
    public void setCompanyName(String companyName) {
        this.companyName = companyName;
    }
    public void setEmployees(Set<Employee> employees) {
        this.employees = employees;
    }
}

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.fancy</groupId>
  <artifactId>hibernate-annotation-many-to-one-example</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>
  <name>hibernate-annotation-many-to-one-example</name>
  <url>http://maven.apache.org</url>
  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>
  
  <dependencies>
    <!-- hibernate jar -->
    <dependency>
      <groupId>org.hibernate</groupId>
      <artifactId>hibernate-entitymanager</artifactId>
      <version>3.3.1.ga</version>
    </dependency>
    <!-- hibernate annotation jar -->
    <dependency>
      <groupId>org.hibernate</groupId>
      <artifactId>hibernate-annotations</artifactId>
      <version>3.3.1.GA</version>
    </dependency>
    <!-- mysql -->
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.17</version>
    </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
  
</project>

Test.java

package com.fancy.test;

import java.util.Iterator;
import java.util.Set;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.cfg.Configuration;
import com.fancy.po.Company;
import com.fancy.po.Employee;
/**
 * -----------------------------------------
 * @文件: Test.java
 * @做者: fancy
 * @郵箱: fancyzero@yeah.net
 * @時間: 2012-6-10
 * @描述: 測試類
 * -----------------------------------------
 */
public class Test {

    public static void main(String[] args) {
        //讀取hibernate配置,默認讀取classpath下的hibernate.cfg.xml
        Configuration conf = new AnnotationConfiguration();    
        //構建session工廠
         SessionFactory sessionFactory = conf.configure().buildSessionFactory();
        //打開session
        Session session = sessionFactory.openSession();
        //開始事務
         session.beginTransaction();
        // * * * * * * * * * * * * * * * * * * * * * * * * * * * *
        //test1(session);   //測試 1
        //test2(session);  //測試  2
        test3(session);   //測試   3
        // * * * * * * * * * * * * * * * * * * * * * * * * * * * *
        //提交事務
         session.getTransaction().commit();
        //關閉session工廠
         sessionFactory.close();
        //關閉session
        session.close();
    }
    public static void test1(Session session){
        Company company = (Company)session.get(Company.class, 1); //發出Company的select語句
         Set<Employee> employee = company.getEmployees();         //不發出Employee的select語句
         System.out.println("Company ：" + company.getCompanyName());
        System.out.println("CountSum：" + employee.size()); //Employee初次被使用,發出select語句
         Iterator<Employee> it = employee.iterator(); //Employee再也不發出select語句
         while(it.hasNext()){
          System.out.println("EmployeeName：" + it.next().getEmployeeName());
        }
    }
    public static void test2(Session session){
       Company company = (Company)session.get(Company.class, 2);//發出Company的select語句
        Set<Employee> employee = company.getEmployees();        //不發出Employee的select語句
        Iterator<Employee> it = employee.iterator(); //發出Employee的select語句
        Employee e = null;
       Boolean first = false;
       while(it.hasNext()){
          e = it.next();
          if(!first){
              System.out.println("EmployeeId：[" + e.getEmployeeId() + "] information will be change");
              e.setEmployeeName("fancy"); //更改僱員名字
            //  session.save(e);  //發出Employee的update語句,不發出Company的update語句
                session.save(company);    //發出Employee的update語句,不發出Company的update語句
                first = true;
            }
            System.out.println("EmployeeName：" + e.getEmployeeName());
        }
    }
    public static void test3(Session session){
        Employee employee = (Employee)session.get(Employee.class, 1);//發出Employee的select語句
         Company  company  = (Company)session.get(Company.class, 1);//發出Company的select語句
         company.setCompanyName("Oracle"); //更改公司名字
    //  session.save(company);//發出Company的update語句,不發出Employee的update語句
         session.save(employee);//發出Company的update語句,不發出Employee的update語句
    }
}