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From Eric Andres <eric.and...@gmail.com>
Subject Re: Discriminator and Table per subclass
Date Fri, 14 Mar 2008 13:11:59 GMT
Thank you for the hint, Ryan.

I tried using the subselect, and it works. However, the way I made it  
work seems awkward, I think I did not fully understand your proposal.   
What I managed to do is this:

I made a result map for the base class:

<resultMap id="eventsMap" class="EventBaseClass">
	.....
         <discriminator javaType="string" column="type"  
jdbcType="VARCHAR">
             <subMap value="UserLoggedIn"  
resultMap="userLoggedInMap"></subMap>
         </discriminator>
  </resultMap>

  and here's the submap for a concrete event type:

   <resultMap id="userLoggedInMap" class="UserLoggedInEvent"  
extends="eventsMap">
       <result property="remoteAdress" select="fetchRemoteAddr"  
column="eventid"/>
       <result property="userAgent" select="fetchUserAgent"  
column="eventId"/>
   </resultMap>

The select queries are all analogous, they look like this:

<select id="fetchRemoteAddr" parameterClass="int" resultClass="string">
         select ip from eventuserloggedin where eventid=#value#
</select>

What I would like to do is, like you described, to have the subselect  
add the parameters to the result map in one shot... Am I on the right  
track or did I miss it completely? Sorry for being slow off the mark...

On Mar 13, 2008, at 7:50 PM, Ryan Shelley wrote:

> Could you use a nested select?  Check out page 34, under "Complex  
> Properties":
> http://ibatis.apache.org/docs/java/pdf/iBATIS-SqlMaps-2_en.pdf
>
> The idea is that one ResultMap contains a complex type that consists  
> of the results from another select.  So if tableA has a primary key,  
> and tableB has a foreign key to the primary key in tableA, you'd  
> have a ResultMap of tableA results, and in each result from tableA  
> exists a List (or Object) of ResultMap(s) that match the foreign key  
> in tableB.  One iBATIS query would execute the primary select to  
> gather tableA results, and then automatically, a separate select  
> will execute to gather the results for each tableA result and insert  
> them into tableA's ResultMap.
>
> I might be incorrect, but I think the docs might be wrong.  It says:
> <result property="category" column="PRD_CAT_ID" select="getCategory"/>
> and it should be:
> <result property="category" column="PRD_ID" select="getCategory"/>
> because you want to map PRD_ID from PRODUCT into the getCategory  
> select.
>
> -Ryan
>
> On Thu, Mar 13, 2008 at 2:54 AM, Eric Andres <eric.andres@gmail.com>  
> wrote:
> Hello,
>
> I have a problem writing a polymorphic query. As I am new to iBatis, I
> started digging the list archive and stumbled upon the discriminator
> and submap tags, and I also found this in the archives: http://www.mail-archive.com/user-java@ibatis.apache.org/msg00070.html
> , my situation is pretty close to Niels', but there was no solution in
> that thread...
> The situation I'm in is this: I have a type hierarchy representing
> events consisting of a base class (call it Event) and a subclass for
> each event type (30+ currently). It's representation in the database
> was done with a table-per-subclass strategy.
>
> I want to write a query that fetches an event based on it's ID.  The
> problem is that I don't know the event type I'm going to fetch in
> advance, and I want to avoid a 30-table join. Is there a way a
> delaying the join to a second query after the 'discrimination'?
> Something like
>
> <resultMap id="Event" class="BaseEvent">
>        ...
>        <result property="ts" column="timestamp/>
>        <discriminator javaType="string" column="type">
>                <subMap value="userLoggedIn"  
> select="addUserLoggedInProps"/>
>                ...
>        </discriminator>
> </resultMap>
>
> ...
>
> <select id="addUserLoggedInProps" parameterClass="int"
> resultMap="userLoggedInEvent">
>        select * from event, userloggedinevent
>        where event.id=userloggedin.eventid and event.id=#value#
> </select>
>
> ...
> <resultMap id="userLoggedInEvent" extends="Event">
>        ...
>        <result property="userId" column="userid"/> <!-- specific to
> userLoggedInEvent -->
>        ...
> </resultMap>
>
>
> Sorry for the lengthy post.  Any help greatly appreciated...
>
> Thanks for your time,
>
>        Eric
>
>


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