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Hibernate關聯映射 --- 一對多實例分析(雙向關聯)

一 概念

最典型的例子是Department和Employee的關系,雙向的關聯

二 代碼分析

(1)Department表

package com.hbsi.domain;

import java.util.Set;

//部門類

public class Department {

    //實現一對多

    private int id;

    private String nameString;

    private Set<Employee> emps; //集合類型,因為有多個員工

    public Department() {

       super();

       // TODO Auto-generated constructor stub

    }

    public Department(int id, String nameString, Set<Employee> emps) {

       super();

       this.id = id;

       this.nameString = nameString;

       this.emps = emps;

    }

    public int getId() {

        return id;

    }

    public void setId(int id) {

       this.id = id;

    }

    public String getNameString() {

       return nameString;

    }

    public void setNameString(String nameString) {

       this.nameString = nameString;

    }

    public Set<Employee> getEmps() {

       return emps;

    }

    public void setEmps(Set<Employee> emps) {

       this.emps = emps;

    }

    @Override

    public String toString() {

       return "Department [id=" + id + ", nameString=" + nameString

              + ", emps=" + emps + "]";

    }

}

(2)Employee類

package com.hbsi.domain;

//員工類      一般主鍵是建在多的一方

public class Employee {

    private int id;

    private String name;

//通過id查詢員工,通過員工 查找部門的話,只能找到部門的id,得不到部門的其他信息

    // 得到的是一個 對象,可以得到員工對應的部門的詳細信息

    private Department depart;

    public Employee() {

       super();

       // TODO Auto-generated constructor stub

    }

    public Employee(int id, String name, Department depart) {

       super();

       this.id = id;

       this.name = name;

       this.depart = depart;

    }

    public int getId() {

       return id;

    }

    public void setId(int id) {

       this.id = id;

    }

    public String getName() {

       return name;

    }

    public void setName(String name) {

       this.name = name;

    }

    public Department getDepart() {

       return depart;

    }

    public void setDepart(Department depart) {

       this.depart = depart;

    }

    public String toString() {

       return "Employee [id=" + id + ", name=" + name + ", depart=" + depart

              + "]";

    }  

}

(3)配置文件

<!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.url">jdbc:mysql:///demo</property>

       <property name="hibernate.connection.username">root</property>

       <property name="hibernate.connection.password">1234</property>

       <!-- 方言 針對哪個數據庫Mysql -->

       <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>

       <!-- 在程序運動的時候,增加自動創建表的屬性,在程序終止 的時候銷毀,但是在表格再次使用時,會重新建 -->

       <property name="hibernate.hbm2ddl.auto">update</property>

       <!-- 執行的sql語句顯示出來 -->

       <property name="hibernate.show_sql">true</property>

       <!-- 指定映射文件的位置 -->

       <mapping resource="com/hbsi/domain/Department.hbm.xml" />

       <mapping resource="com/hbsi/domain/Employee.hbm.xml" />

    </session-factory>

</hibernate-configuration>

(4)Department的映射文件

    <?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.hbsi.domain">

    <!-- 缺省table 表明和類名是一樣的 -->

    <class name="Department" table="department">

       <id name="id" column="id">

           <generator class="native" />

       </id>

       <property name="name" column="name" />

       <!-- 集合屬性的體現  一對多 -->

       <set name="emps">

           <!--  根據外鍵的值查詢,而不是查詢所有的記錄-->

           <key column="depart_id"/>

           <!-- 告訴Hibernate emps是集合屬性,是一對多的關聯 -->

           <one-to-many class="Employee" />  

       </set>

    </class>

</hibernate-mapping>

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