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From Kris Jenkins <krisajenk...@yahoo.co.uk>
Subject Re: What is N+1
Date Wed, 09 Feb 2005 12:28:43 GMT

>Well, I think you need only simple join in your sql, no extra features of
>ibatis needed:
>select * from CHILD, PARENT where parent_id=PARENT.id;
>am I right?
Well, that's the right query, but only if you use groupBy.  Assuming 
you're trying to get Parent objects populated with their correct Child 
objects, you query will return something like:

parent_id | child_id
1         | a
1         | b
1         | c
2         | d

Without groupBy in your resultMap, you'll end up with 3 parent objects, 
each with one child.  What you wanted was 2 parents, one with three 

So you're right, groupBy allows you to do this with one query, but 
before v2.0.9 you'd've needed two separate ones to get the right result.


Kris Jenkins
Email:  kris@jenkster.com
Blog:   http://cafe.jenkster.com/
Wiki:   http://wiki.jenkster.com/

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