Hibernate之单向一对多映射(使用maven构建)

在实际开发中，一对多的例子有很多，比如一个部门对应多个员工，这就是一种典型一对多的关系，在Hibernate中使用一对多映射可以使用一方来管理多方，这显然是很方便的。在本例中，使用了2个实体，一是员工employee，另外一个是部门department。

首先创建2张表：

接下来就是创建一个project了，整个工程的骨架如下图所示：

先看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>Demo</groupId><artifactId>HibernateDemo</artifactId><version>0.0.1-SNAPSHOT</version><packaging>jar</packaging><name>HibernateDemo</name><url>http://maven.apache.org</url><properties><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding></properties><dependencies><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.2</version><scope>test</scope></dependency><!-- 添加Hibernate依赖 --><dependency><groupId>org.hibernate</groupId><artifactId>hibernate-core</artifactId><version>4.3.0.Final</version></dependency><!-- 添加Log4J依赖 --><dependency><groupId>log4j</groupId><artifactId>log4j</artifactId><version>1.2.16</version></dependency><dependency><groupId>org.slf4j</groupId><artifactId>slf4j-nop</artifactId><version>1.6.4</version></dependency><!-- mysql数据库的驱动包 --><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.6</version></dependency></dependencies></project>

再看两个实体类Employee和Department：

package entity;public class Employee {private int empId;private String empName;public Employee() {super();}public Employee(String empName) {super();this.empName = empName;}public Employee(int empId, String empName) {super();this.empId = empId;this.empName = empName;}public int getEmpId() {return empId;}public void setEmpId(int empId) {this.empId = empId;}public String getEmpName() {return empName;}public void setEmpName(String empName) {this.empName = empName;}@Overridepublic String toString() {return "Employee [empId=" + empId + ", empName=" + empName + "]";}}

package entity;import java.util.Set;public class Department {private int deptId;private String deptName;private Set<Employee> employees;public Department() {super();}public Department(String deptName) {super();this.deptName = deptName;}public Department(int deptId, String deptName) {super();this.deptId = deptId;this.deptName = deptName;}public int getDeptId() {return deptId;}public void setDeptId(int deptId) {this.deptId = deptId;}public String getDeptName() {return deptName;}public void setDeptName(String deptName) {this.deptName = deptName;}public Set<Employee> getEmployees() {return employees;}public void setEmployees(Set<Employee> employees) {this.employees = employees;}@Overridepublic String toString() {return "Department [deptId=" + deptId + ", deptName=" + deptName + ", employees=" + employees + "]";}}

注意，因为是单向的一对多关联映射，所以在一方，也就是department方，建立一个Set类型的变量来保存多方的信息。同样，

在hbm.xml文件里面也会体现出这一点。

Employee.hbm.xml:

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><!-- Generated 2017-10-8 19:42:28 by Hibernate Tools 3.5.0.Final --><hibernate-mapping>    <class name="entity.Employee" table="EMPLOYEE">        <id name="empId" type="java.lang.Integer">            <column name="EMP_ID" />            <generator class="native" />        </id>        <property name="empName" type="java.lang.String">            <column name="EMP_NAME" />        </property>    </class></hibernate-mapping>

Department.hbm.xml:

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><!-- Generated 2017-10-8 19:42:28 by Hibernate Tools 3.5.0.Final --><hibernate-mapping>    <class name="entity.Department" table="DEPARTMENT">        <id name="deptId" type="java.lang.Integer">            <column name="DEPT_ID" />            <generator class="native" />        </id>        <property name="deptName" type="java.lang.String">            <column name="DEPT_NAME" />        </property>        <set name="employees" cascade="all" table="EMPLOYEE">        <key column="DEPT_ID"></key>        <one-to-many class="entity.Employee"/>        </set>    </class></hibernate-mapping>

然后就是hibernate的主配置文件了：

hibernate.cfg.xml:

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-configuration PUBLIC"-//Hibernate/Hibernate Configuration DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"><hibernate-configuration>    <session-factory>        <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>        <property name="hibernate.connection.password">root</property>        <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/hibernate_demo</property>        <property name="hibernate.connection.username">root</property>        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>                <property name="show_sql">true</property>        <property name="format_sql">true</property>                <mapping resource="Department.hbm.xml"/>        <mapping resource="Employee.hbm.xml"/>    </session-factory></hibernate-configuration>

接下来是工具类HibernateDAOHelper：

package util;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.boot.registry.StandardServiceRegistryBuilder;import org.hibernate.cfg.Configuration;import org.hibernate.service.ServiceRegistry;public class HibernateDAOHelper {private static SessionFactory sessionFactory;private static Session session;static {//从class目录自动获取hibernate主配置文件Configuration config = new Configuration().configure();//获取服务注册对象ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(config.getProperties()).build();//获取会话工厂sessionFactory = config.buildSessionFactory(serviceRegistry);}//获取会话对象public static Session getSession() {session = sessionFactory.openSession();return session;}//关闭会话public static void closeSession() {if(session!=null) {session.close();}}}

最后是测试类，分别给出了CRUD的测试：

package test;import java.util.HashSet;import java.util.Set;import org.hibernate.Session;import org.hibernate.Transaction;import org.junit.Test;import entity.Department;import entity.Employee;import util.HibernateDAOHelper;public class TestDemo{@Testpublic void addTest() {Department dept = new Department("部门1");Employee emp1 = new Employee("员工1");Employee emp2 = new Employee("员工2");Set<Employee> empSet = new HashSet<Employee>();empSet.add(emp1);empSet.add(emp2);dept.setEmployees(empSet);Session session = HibernateDAOHelper.getSession();Transaction tx = session.beginTransaction();session.save(dept);tx.commit();HibernateDAOHelper.closeSession();}@Testpublic void queryTest() {Session session = HibernateDAOHelper.getSession();Department dept = (Department) session.get(Department.class, 1);System.out.println(dept);}@Testpublic void updateTest() {Session session = HibernateDAOHelper.getSession();Transaction tx = session.beginTransaction();Department dept = (Department) session.get(Department.class, 1);Employee emp = (Employee) session.get(Employee.class, 2);dept.getEmployees().remove(emp);session.update(dept);tx.commit();HibernateDAOHelper.closeSession();}@Testpublic void deleteTest() {Session session = HibernateDAOHelper.getSession();Transaction tx = session.beginTransaction();Department dept = (Department) session.get(Department.class, 1);session.delete(dept);tx.commit();HibernateDAOHelper.closeSession();}}

在执行测试前，数据库里是没有数据的：

现在执行添加方法：

再执行查询方法：

执行更新方法：

执行删除方法：