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‘);

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;@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：多对一,cascade：级联,请参考上一篇      * fetch = FetchType.LAZY,延迟加载策略,如果不想延迟加载可以用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;    }}

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;@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 与 OneToOne相似的也用mappedBy,参考了Employee     */    @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;    }}

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;public class Test {    public static void main(String[] args) {        //读取hibernate配置,默认读取classpath下的hibernate.cfg.xml        Configuration conf = new AnnotationConfiguration();            //构建session工厂         SessionFactory sessionFactory = conf.configure().buildSessionFactory();        //打开session        Session session = sessionFactory.openSession();        //开始事务         session.beginTransaction();        // * * * * * * * * * * * * * * * * * * * * * * * * * * * *        //test1(session);   //测试 1        //test2(session);  //测试  2        test3(session);   //测试   3        // * * * * * * * * * * * * * * * * * * * * * * * * * * * *        //提交事务         session.getTransaction().commit();        //关闭session工厂         sessionFactory.close();        //关闭session        session.close();    }    public static void test1(Session session){        Company company = (Company)session.get(Company.class, 1); //发出Company的select语句         Set<Employee> employee = company.getEmployees();         //不发出Employee的select语句         System.out.println("Company ：" + company.getCompanyName());        System.out.println("CountSum：" + employee.size()); //Employee初次被使用,发出select语句         Iterator<Employee> it = employee.iterator(); //Employee不再发出select语句         while(it.hasNext()){          System.out.println("EmployeeName：" + it.next().getEmployeeName());        }    }    public static void test2(Session session){       Company company = (Company)session.get(Company.class, 2);//发出Company的select语句        Set<Employee> employee = company.getEmployees();        //不发出Employee的select语句        Iterator<Employee> it = employee.iterator(); //发出Employee的select语句        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"); //更改雇员名字            //  session.save(e);  //发出Employee的update语句,不发出Company的update语句                session.save(company);    //发出Employee的update语句,不发出Company的update语句                first = true;            }            System.out.println("EmployeeName：" + e.getEmployeeName());        }    }    public static void test3(Session session){        Employee employee = (Employee)session.get(Employee.class, 1);//发出Employee的select语句         Company  company  = (Company)session.get(Company.class, 1);//发出Company的select语句         company.setCompanyName("Oracle"); //更改公司名字    //  session.save(company);//发出Company的update语句,不发出Employee的update语句         session.save(employee);//发出Company的update语句,不发出Employee的update语句    }}