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From "James, Steven" <Steven.Ja...@logicacmg.com>
Subject RE: Several dumb questions
Date Tue, 15 Mar 2005 12:11:13 GMT
Your idea of mapping students to courses is correct, although 
you do not have to have a pk in the mapping table if a studentid and course id
row are unique which by the sounds of it they are. The pk is a composite. But if
you want a pk key then you can. 

As to updating these mappings then if a new course is added then just provide a add couseMapping
function
with the 2 keys. The question you should ask youself is time versus money, if you have the
time and the
project has the cash then provide crud routines for each ie update mapping, delete mapping,
new mapping and
in you buisness object representing your mappings if you have them add a type field which
contains
a value for update, new, delete etc.. This way your application logic can work out which routine
to call.

If like many projects you do not have time, and you want a nice simple design then delete
and insert as you have 
suggested. Do this in a batch transaction to minimise database interaction and you got a nice
simple solution.

At your service layer if dealing with objects this should be simple. Add them to the batch
as you iterate.
then execute the batch.

good luck

Steve


-----Original Message-----
From: Vamsee Kanakala [mailto:vamlists@gmail.com]
Sent: Tue 3/15/2005 11:11 AM
To: ibatis-user-java@incubator.apache.org
Subject: Several dumb questions
 
Hello,

This is more of a database design question than an ibatis question, I 
hope you guys don't mind :) Here goes:

I have a table called students, and students can be assigned to several 
batches ('course' would be a better name, I think). So, I'm using a 
students_batches_map which basically contains  and id(primary key), 
student_id and batch_id.

First of all, is this a good idea? Is there any better way I can express 
such a relation? Second, if I have to update the number of batches a 
student is associated with, I can think of only one way: drop all 
batches a student is associated with and insert new selections again. 
Again, is this a good idea?

Finally, I'm having to iterate through the list of batches and insert 
each record into the students_batches_map. Is there a better way?

TIA,
Vamsee.


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