Hibernate多表查询实践小结（转）

Hibernate多表查询实践总结（转）

实在无聊，前段时间做了个对单表的ZCGC(增删改查)，练了练手，虽然做过，但还是碰到了不少问题，让自己对struts+hibernate模式开发更加熟练了点。今天，我做多表的复习的时候，又碰到问题了，现在将关键点记录下来，以免日后再有相同问题出现，以便查阅。
我做的两张表：一张department表，一张employee表，建表语句如下：
drop table employee
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 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">       
<key>
              <column name="parentID" precision="5" scale="0"
                  not-null="true" />
           </key>
           <one-to-many
              />
       </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 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。

另外种方法
写个DocumentDetail对象，然后获得查询结果集合
select new com.cetc.bean.util.vo.DocumentDetail(da.contentid,dd.id,dd.filename,dd.filesource,dd.filesize,dd.mimetype,dd.author,dd.filepath) from DocumentDetail dd,ContentAttachment da where dd.id=da.documentid
构造函数一定要写好
public DocumentDetail(String contentid,String documentid,String fileName,String fileSource,Long fileSize,String mimeType,String author,String filePath){
   this.contentid = contentid;
   this.documentid = documentid;
   this.fileName = fileName;
   this.fileSource = fileSource;
   this.fileSize = fileSize;
   this.mimeType = mimeType;
   this.author = author;
   this.filePath = filePath;
}