多表查询一

create table EMPLOYEE
(
ID      NUMBER(10) not null,
parentID   number(10),
NAME     VARCHAR2(20),
AGE      NUMBER(3),
PASSWARD VARCHAR2(12),
CSRQ     DATE,
PICTURE varchar(12),
primary key(id),
foreign key(parentID) references department(id)
)
drop table department
create table department
(
id number(10) not null,
dep_id varchar2(20),
dep_mc varchar2(20),
primary key(id)
)
其中，employee表中的parentID是department表的外键，department和employee表是一对多的关系，反过来是多对一的关系。怎么叫都可以。
Department.hbm.xml代码如下：
<hibernate-mapping>
    <class name="com.dudeng.employee.hibernate.vo.Department"
       table="DEPARTMENT" schema="DUDENG">
       <id name="id" type="java.lang.Long">
           <column name="ID" precision="10" scale="0" />
           <generator class="sequence">
              <param name="sequence">seq_department</param>
           </generator>
       </id>
       <property name="dep_id" type="java.lang.String">
           <column name="DEP_ID" length="20" not-null="false" />
       </property>
       <property name="dep_mc" type="java.lang.String">
           <column name="DEP_MC" length="20" not-null="false" />
       </property>
       <set name="employees" inverse="true"> 注：inverse="true"表示由多一方来维护      
           <key>
              <column name="parentID" precision="5" scale="0"
                  not-null="true" />
           </key>
           <one-to-many
              class="com.dudeng.employee.hibernate.vo.Employee" />
       </set>    </class>
</hibernate-mapping>
Employee.hbm.xml的代码如下：
<hibernate-mapping>
    <class name="com.dudeng.employee.hibernate.vo.Employee"
       table="EMPLOYEE" schema="DUDENG">
       <id name="id" type="java.lang.Long">
           <column name="ID" precision="10" scale="0" />
           <generator class="sequence">
              <param name="sequence">seq_employee</param>
           </generator>
       </id>
       <many-to-one name="department"   class="com.dudeng.employee.hibernate.vo.Department">
                <column name="parentID" precision="5" scale="0" not-null="true" />       </many-to-one>
       <property name="name" type="java.lang.String">
           <column name="NAME" length="20" not-null="false" />
        </property>
       <property name="age" type="java.lang.Long">
         <column name="AGE" precision="3" scale="0" not-null="false" />
       </property>
       <property name="passward" type="java.lang.String">
           <column name="PASSWARD" length="12" not-null="false" />
        </property>
       <property name="csrq" type="java.util.Date">
           <column name="CSRQ" length="7" not-null="false" />
       </property>
       <property name="picture" type="java.lang.String">
           <column name="PICTURE" length="20" not-null="false"/>
       </property>
    </class>
</hibernate-mapping>
查询结果集合：
List list = null;
String QueryStr = "from Employee emp,Department dep where emp.department = dep.id";
EmployeeBiz empbiz = EmployeeBiz.getInstance();
list = empbiz.find(QueryStr);
for (int i = 0; i < list.size(); i++)
{
    Object[] obj = (Object[]) list.get(i);
    for (int j = 0; j < obj.length; j++)
    {
       if (obj[j] instanceof Employee)
       {
           Employee emp = (Employee) obj[j];
           System.out.print(emp.getName());
       }
elseif (obj[j] instanceof Department)
       {
           Department dep = (Department) obj[j];
           System.out.print(dep.getDep_mc());
       }
    }
    System.out.println();
}

以上特别注意的地方：emp.department不能写成emp.parentID，我上网查了半天才找出原因的。开始写成emp.parentID了，后来改成emp.department程序运行正常了