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From Kris Rasmussen <kristapes...@yahoo.com>
Subject n+1 is triggering multiple queries, 3?
Date Sat, 09 Jul 2005 09:36:04 GMT
I have an n+1 mapping. When I look at mysql health in the administrator it apears that 3 queries
are being executed instead of one. The first query gets executed when I retrieve the intial
object via queryForObject. The next two queries are being executed when I attempt to access
the List which stores the related objects from the main object. I am very curious what is
going on since I don't know how Ibatis could even know what query to execute to get the items
later?
 
The following maps are used to retrive a single instance of classB with all of its classA
children stored in one of its properties which is of course a list.
 

<resultMap id="getClassAResult" class="classA">

... some basic properties

</resultMap>



<resultMap id="getClassBResult" class="classB">

<result property="primKey1" column="classB.primKey1"/>

<result property="primKey2" column="classB.primKey2"/>

... some more properties

</resultMap>



<resultMap id="getClassBWithClassAsResult" class="classB" extends="getClassBResult" groupBy="primKey1,primKey2">

<result property="classAs" resultMap="namespace.getClassAResult"/>

</resultMap>

 

and my select statement...

<select id="getClassBWithClassAs" parameterClass="keyClass" resultMap="getClassBWithClassAsResult">

SELECT classB.*,classA.* FROM classB ,classA

WHERE classB.primKey1=#primKey1# AND classB.primKey2=#primKey2# AND gallery_image.SiteId=#siteId#
AND gallery_image.BlockId=#blockId#

GROUP BY classB.primKey1,classB.primKey2,classA.primKey3

</select>



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