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From "Clinton Begin" <clinton.be...@gmail.com>
Subject RE: PLEASE HELP - self-joins to obtain a tree structure
Date Fri, 19 Oct 2007 14:15:26 GMT
Your JDBC driver may only allow a certain number of result sets open at a
time (per connection).  If your tree is a fixed depth, you can see if you
can try to configure it such that you have enough (in ms sql server, make
sure your select mode is "cursor").

If your tree is arbitrarily sized or simply very deep, then this whole
approach may be very inefficient and you'd be better off trying something
else.

You could try doing an actual SQL self join, or just load the flat structure
into an array of objects and use a more efficient tree mapping algorithm to
link it all up.  

It's not a super easy or clean thing to do...but my first question to you
would be...do you actually need the whole tree?  And does it need to be a
tree?

Regards,
Clinton


-----Original Message-----
From: Mark McKenzie [mailto:mark.mckenzie@pcmsgroup.com] 
Sent: October-19-07 1:15 AM
To: user-java@ibatis.apache.org
Subject: PLEASE HELP - self-joins to obtain a tree structure

Hi, I am trying to use the following IBatis SQL map to 
retrieve a single object (ProductGroup) which will contain 
a parent object of the same type. The parent object itself 
could also potentially have a parent object ?.. and so on 
and so on until we reach the top of the tree:

  

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE sqlMap PUBLIC "-//iBATIS.com//DTD SQL Map 
2.0//EN" "http://www.ibatis.com/dtd/sql-map-2.dtd">

  

<sqlMap namespace="ProductGroup">

  

   <resultMap id="result" class="ProductGroup">

     <result property="primaryKey"    column="PRGP_ID"/>

     <result property="code"          column="PRGP_CODE"/>

     <result property="name"          column="PRGP_NAME"/>

     <result property="parentGroup" 
  column="groupId=PARENT_ID" 
select="ProductGroup.getById"/>    

   </resultMap> 

  

   <!-- fetch a complex product group object containing 
all parent groups -->

   <select id="getById" resultMap="result">

     SELECT prgp.*

           ,pgsl.prgp_id AS PARENT_ID

      FROM product_group prgp

              INNER JOIN prodgp_str_link pgsl  ON 
prgp.prgp_id = pgsl.prgp_child_id

       WHERE prgp.prgp_id = #groupId#

   </select>

   

</sqlMap>

  

Unfortunately this does not appear to work when I use it 
to retrieve a product group with more than 1 parent 
object. Here is a partial stack trace of the problem I 
get:

  

   <!--
     com.pcmsgroup.v21.star2.inf.dao.exception.PersistenceException: 
SqlMapClient operation; uncategorized SQLException for SQL 
[]; SQL state [null]; error code [0];   
--- The error occurred in conf/ibatis/ProductGroup.xml.  
--- The error occurred while applying a result map.  
--- Check the ProductGroup.result.  
--- Check the result mapping for the 'parentGroup' 
property.  
--- Cause: 
com.ibatis.common.jdbc.exception.NestedSQLException:   
--- The error occurred in conf/ibatis/ProductGroup.xml.  
--- The error occurred while applying a result map.  
--- Check the ProductGroup.result.  
--- The error happened while setting a property on the 
result object.  
--- Cause: 
com.microsoft.sqlserver.jdbc.SQLServerException: The 
result set is closed.; nested exception is 
com.ibatis.common.jdbc.exception.NestedSQLException:   
--- The error occurred in conf/ibatis/ProductGroup.xml.  
--- The error occurred while applying a result map.  
--- Check the ProductGroup.result.  
--- Check the result mapping for the 'parentGroup' 
property.  
--- Cause: 
com.ibatis.common.jdbc.exception.NestedSQLException:   
--- The error occurred in conf/ibatis/ProductGroup.xml.  
--- The error occurred while applying a result map.  
--- Check the ProductGroup.result.  
--- The error happened while setting a property on the 
result object.  
--- Cause: 
com.microsoft.sqlserver.jdbc.SQLServerException: The 
result set is closed.
         at 
com.pcmsgroup.v21.star2.inf.dao.BaseSqlMapClientDao.queryForObject(BaseSqlMa
pClientDao.java:166)
         at 
com.pcmsgroup.v21.star2.persistence.productgroup.ProductGroupDAO.getGroup(Pr
oductGroupDAO.java:46)
  
Does anyone have any idea what the issue is and possibly 
how to resolve it?
  
Many Thanks, Mark

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