Thanks Ingmar Lötzsch for the reply.
Actually I was simplifying the context from 1-M to 1-1 for discussion so left
groupBy attribute mistakenly.
The problem at hand is that Teacher has students (1:M). Student must have some
teacher assigned to him but teacher does not necessarily need to have some
student.
So I go ahead and load some teacher and it will load all students associated
with it as Teacher would have List<Student>. But what I want is that student
also have a reference to Teacher. Following code would explain what I want:
class Teacher {
List<Student> students;
....
}
class Student {
Teacher teacher;
....
}
SQL Map config file
<resultMap id="TeacherResultMap" class="Teacher" groupBy="id" >
<result property="id" />
<result property="name" />
<result property="students" resultMap="JOB.StudentResultMap"/>
</resultMap>
<resultMap id="StudentResultMap" class="Student" >
<result property="id" column="stu_id"/>
<result property="name" column="stu_Name"/>
<result property="teacher" resultMap="JOB.TeacherResultMap"/>
</resultMap>
<select id="findTeacher" parameterClass="int" resultMap="TeacherResultMap11">
select t.id , t.name , s.id as stu_id, s.name as stu_Name , s.tid as
stu_tid from Teacher t left join student s on t.id = s.tid where t.id = #value#
</select>
The line in red would make cyclic reference to associate teacher with student
and stack overflow so I can't do that but effectively I want to do that.
I understand your point where you tell me I could associate teacher for each
student in business logic but I am wondering if there is any way that both
sides of relationship could hold a reference of other side of relationship
implicitly.
Thanks,
Petr
--- On Wed, 1/21/09, Ingmar Lötzsch <[email protected]> wrote:
From: Ingmar Lötzsch <[email protected]>
Subject: Re: 2 Way 1-1 relationship
To: [email protected]
Date: Wednesday, January 21, 2009, 4:38 PM
Petr V. schrieb:
> I want to have two way relationship like Teacher contains reference of
> Student and Student contains reference of Teacher. Is it even possible
> in iBatis ?
>
> class Teacher {
> Student sid;
> ....
> }
>
> class Student {
> Teacher teacher;
> ....
> }
>
>
> I wrote the following SQL config file and as expected I got stack over
> flow due to recursion.(Map referring each other)
>
> <resultMap id="TeacherResultMap99" class="Teacher"
groupBy="id" >
> <result property="id" column="tea_id"/>
> <result property="name" column="tea_name" />
> <result property="sid"
resultMap="JOB.StudentResultMap99"/>
> </resultMap>
>
> <resultMap id="StudentResultMap99" class="Student"
>
> <result property="id" column="stu_id"/>
> <result property="name" column="stu_Name"/>
> <result property="teacher"
resultMap="JOB.TeacherResultMap99"/>
> </resultMap>
>
>
> <select id="findStudent" parameterClass="int"
> resultMap="StudentResultMap99">
> select t.id as tea_id , t.name as tea_name , s.id as stu_id, s.name
> as stu_Name , s.tid as stu_tid from Teacher t left join student s on
> t.id = s.tid where s.id = #value#
> </select>
SELECT
t.id AS tea_id,
t.name AS tea_name,
s.id AS stu_id,
s.name AS stu_name,
s.tid AS stu_tid
FROM teacher t
LEFT JOIN student s ON t.id = s.tid
WHERE s.id = #value#
I don't understand, why you use a LEFT JOIN to table student. You
provide the ID of the student as a parameter. If there exists a
corresponding row, you get a result, if not, you don't. You can use a
RIGHT JOIN instead, if there exist students without teacher.
If you have a real 1 to 1 relationship, omit the groupBy attribut and
the result element for property "sid". Otherwise use
List<Student> in
class Teacher.
StudentDAOImpl
{
public Student findStudent(Integer id)
{
return (Student)
getSqlMapClientTemplate().queryForObject("<NAMESPACE>.findStudent",
id)
}
}
Somewhere in your business code you can write something like that:
Integer id = ...
Student student = this.studentDAO.findStudent(id);
if (student != null)
{
Teacher teacher = student.getTeacher();
if (teacher != null)
{
teacher.setStudent(student);
}
}
