Hibernate 关联映射入门吧

        在软件开发中，类与类之间最普遍的关系就是关联关系，而且关联是有方向的。

 通过类图展示的方式讲解类与类之间的关联关系，类与类之间存在着单向关联，也存在着双向关联。如下图所示：

 多对一关联和一对多双向关联：

  例子：

  以员工类（Emp）和部门类（Dept）为例

1.先建立两个实体类

package cn.entity;

public class Emp {
private Integer empNo;
private String empName;
private Dept dept;
public Integer getEmpNo() {
    return empNo;
}
public void setEmpNo(Integer empNo) {
    this.empNo = empNo;
}
public String getEmpName() {
    return empName;
}
public void setEmpName(String empName) {
    this.empName = empName;
}
public Dept getDept() {
    return dept;
}
public void setDept(Dept dept) {
    this.dept = dept;
}
public Emp(Integer empNo, String empName, Dept dept) {
    super();
    this.empNo = empNo;
    this.empName = empName;
    this.dept = dept;
}
public Emp() {
    super();
    // TODO Auto-generated constructor stub
}

}

package cn.entity;

import java.util.HashSet;
import java.util.Set;



public class Dept {
private Integer deptNo;
private String deptName;
private Set<Emp> emp=new HashSet<Emp>();

public Set<Emp> getEmp() {
    return emp;
}
public void setEmp(Set<Emp> emp) {
    this.emp = emp;
}
public Integer getDeptNo() {
    return deptNo;
}
public void setDeptNo(Integer deptNo) {
    this.deptNo = deptNo;
}
public String getDeptName() {
    return deptName;
}
public void setDeptName(String deptName) {
    this.deptName = deptName;
}
public Dept(Integer deptNo, String deptName) {
    super();
    this.deptNo = deptNo;
    this.deptName = deptName;
}
public Dept() {
    super();
    // TODO Auto-generated constructor stub
}

}

2.书写小配置文件

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="cn.entity">

        <class name="Emp" table="EMP">
                <id name="empNo">
                        <generator class="native"/>
                </id>
                <!-- assigned 程序员赋值  native后台DB赋值-->
                <property name="empName" />
                <many-to-one name="dept" class="Dept" column="deptid"></many-to-one>
                       
        </class>
</hibernate-mapping>

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="cn.entity">

        <class name="Dept" table="DEPT">
                <id name="deptNo">
                        <generator class="native"/>
                        
                </id>
                <!-- assigned 程序员赋值  native后台DB赋值-->
                <property name="deptName" />
               
               <set name="emp" cascade="save-update" inverse="true"><!-- casecade级联:取值 ： none save-update delete all -->
               <!-- inverse 默认值 false 主动方 维护关联关系 -->
               <key column="deptid"></key><!-- key:这里是多的一方定义的外键 -->
               <one-to-many class="Emp"/><!-- 多的一方的实体类型 -->
               </set>        
        </class>
</hibernate-mapping>

3.大配置关联小配置

<?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>

        <!-- Database connection settings 数据库连接配置-->
        <property name="connection.driver_class">oracle.jdbc.OracleDriver</property>
        <property name="connection.url">jdbc:oracle:thin:@localhost:1521:orcl</property>
        <property name="connection.username">wth</property>
        <property name="connection.password">1509184562</property>

        <!-- JDBC connection pool (use the built-in) -->
        <property name="connection.pool_size">1</property>

        <!-- SQL dialect 方言-->
        <property name="dialect">org.hibernate.dialect.Oracle10gDialect</property>


        <!-- Echo all executed SQL to stdout 在控制台打印后台sql语句-->
        <property name="show_sql">true</property>
        <!-- 格式化语句 -->
       <property name="format_sql">true</property>
        <!-- Drop and re-create the database schema on startup -->
     <property name="hbm2ddl.auto">create</property> 
          <!-- 关联小配置 -->
        <mapping resource="cn/entity/Emp.hbm.xml" />
     <mapping resource="cn/entity/Dept.hbm.xml" />
    </session-factory>

</hibernate-configuration>

4.书写测试类（使用单元测试方法）

package cn.happy;

import java.util.List;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;

import cn.entity.Dept;
import cn.entity.Emp;
import cn.entity.HibernateUtil;

public class OneToMany {
    //多对一关联
@Test
public void OneToManyTewst(){
    

        Session session = HibernateUtil.currentSession();
        Transaction tx = session.beginTransaction();
        Emp emp=new Emp();
        Dept dept=new Dept();
        emp.setEmpName("小河");
        emp.setDept(dept);    
        dept.setDeptName("保安部");
        session.save(emp);
        session.save(dept);
        tx.commit();
        HibernateUtil.closeSession();
}
//一对多双向关联
//主要是set集合
@Test
public void ManyToOneTest(){
    Session session = HibernateUtil.currentSession();
    List<Dept> dept=session.createQuery("from Dept").list();
    for (Dept item : dept) {
        System.out.println(item.getDeptName());
        System.out.println("*******************");
        for (Emp emp : item.getEmp()) {
            System.out.println(emp.getEmpName());
        }
    }
}
}

 今天就到这里，下次见！！！