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https://issues.apache.org/jira/browse/IBATIS-375?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Clinton Begin closed IBATIS-375.
--------------------------------
Resolution: Fixed
Fix Version/s: 2.3.4
applied patch
> Provide a way for not creating items from nested ResultMaps when the items
> contain only null values
> ---------------------------------------------------------------------------------------------------
>
> Key: IBATIS-375
> URL: https://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
> Fix For: 2.3.4
>
> Attachments: BasicResultMap.java, BasicResultMapping.java,
> iBATIS-375.patch, sql-map-2.dtd, SqlMapParser.java
>
>
> 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.
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