Foreign key issue

ajse · **Joined:** Fri Apr 01, 2005 2:15 am **Posts:** 14

Hi all,
I have two tables-1.student(student_id,student_name), 2.info(info_id,student_id,city).Here student_id is the pk of student and fk of info.I want to know that should i mention the pk and fk constrain during my sql create table statement or it is sufficient to mention the mapping tags in the hbm file.If is it in hbm file than how to write this.I have gone through the Hibernate docs but could not find.

I also want that whenever I create a student record ,info record should also be created (student_id should be inserted in both the table).It is possible or not.Please help.

With regards,
Ajse

mrtz · **Joined:** Mon Aug 01, 2005 3:10 pm **Posts:** 22

Hi Ajse,

Yes, the database table create sql should have the PK/FK constraints. Hibernate works on top of that and your Hibernate mappings should also have the corresponding settings for the relationships.

You need to spend some time reading the docs. You will find that the section on Associations explains what you are trying to do: http://www.hibernate.org/hib_docs/v3/re ... sociations

As for automatic creation of records for related tables, Hibernate supports it with specific configuration settings in the mappings. Look for the "cascade" attribute. It's setting can control how your insert/updates cascade through an object graph - its use depends on application specific needs.

Mrtz

ajse · **Joined:** Fri Apr 01, 2005 2:15 am **Posts:** 14

Hi mrtz,
Thanks for your reply.It was really helpful.But I could not find how should
I rate your reply.
with regards,
Ajse

lovkiys · **Joined:** Mon Sep 22, 2003 5:18 am **Posts:** 28

You need to map one-to-many relationship between Student and Info entities. In Student mapping you may specify such relationship as following:

Code:

    <class name="com.my.domain.Student"
        table="STUDENT">

        <id
            name="id"
            column="STUDENT_ID"
            type="long">
        </id>
        ... other fields mapping goes here

        <set
            name="infos"
            lazy="false"
            cascade="save-update"
            sort="unsorted">

            <key column="STUDENT_ID" />
            <one-to-many class="com.my.domain.Info" />

        </set>

       ....the rest of you mapping file

    </class>

In this case, all you need to do is to create Student, set its properties, also create Info object, and add it to infos set:

Code:

 Student student = new Student();
 student.setName("name");
 ...
 Info info = new Info();
 info.setInfoDetails(details);
 //obtain set either from Student.getInfos() or create new one
 Set infos = new HashSet();
 infos.add(info);
 //update infos set in Student
 student.set(infos);
//now lets' save data
 session.save(student);

All nested objects that has primary key value equals to 'unsaved-value' Hibernate will try to persist by inserting new rows in correspondent tables.
This is done by specifying cascade="save-update" in mapping file

Hope this would help to shed the light on Hibernate magic =)
Feel free to ask for details

mrtz · **Joined:** Mon Aug 01, 2005 3:10 pm **Posts:** 22

Hi Asje,
You should be able to click on the link below my posting such as:
Post rating: Please rate this answer to give credits to the poster! Did it solve the problem? Yes / No
-Mrtz