Provide a way for not creating items from nested ResultMaps when the items
contain only null values
---------------------------------------------------------------------------------------------------
Key: IBATIS-375
URL: http://issues.apache.org/jira/browse/IBATIS-375
Project: iBatis for Java
Issue Type: Improvement
Components: SQL Maps
Affects Versions: 2.2.0
Reporter: Stefan Langer
Taken the following resultmaps (uneeded parts are left out) for a simple
domainmodel where notebook contains 0 or more pages.
<resultMap class="notebook" groupBy="id" id="notebookResult">
<result column="NB_ID" jdbcType="VARCHAR" property="id"/>
<result javaType="java.util.List" property="pages"
resultMap="Note.pageResult"/>
</resultMap>
<resultMap class="page" groupBy="id" id="pageResult">
<result column="P_ID" jdbcType="VARCHAR" property="id"/>
</resultMap>
and the following select statement:
<select id="selectNotebook" parameterClass="java.lang.String"
resultMap="notebookResult">
SELECT nb.id as nb_id, p.id as p_id,
FROM notebook nb LEFT JOIN page p ON nb.id = p.notebook_id
WHERE nb.id = #id#
</select>
Do to the left join this query will always result in at least one page being
created even though the pages are actually empty.
It would be nice if the mapping framework could somehow not create these empty
objects.
The following suggestions come to mind:
Either do not create objects where all parameters are null (this indicates the
left or right join scenario)
or provide a way to tag a property in the resultMap which may not be null in
order for the object to be created.
Example:
<resultMap class="page" groupBy="id" id="pageResult">
<result column="P_ID" jdbcType="VARCHAR" property="id"
doNotCreateOnNull="true"/>
</resultMap>
This would greatly ease the use of complex mappings where one wants to prevent
the dreaded N+1 Select Problem.
--
This message is automatically generated by JIRA.
-
If you think it was sent incorrectly contact one of the administrators:
http://issues.apache.org/jira/secure/Administrators.jspa
-
For more information on JIRA, see: http://www.atlassian.com/software/jira
