Hibernate
多表查询实践总结（
2006-11-24
）
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
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"
>
<
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());
}
else
if
(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。
最后在页面上显示：
<
logic:present
name
=
"employees"
scope
=
"request"
>
<
logic:iterate
id
=
"objs"
name
=
"employees"
indexId
=
"number"
>
<
tr
>
<
td
>
${objs[0].name}
</
td
>
<
td
>
${objs[1].dep_mc}
</
td
>
</
tr
>
</
logic:iterate
>
</
logic:present
>
