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Posted to dev@ibatis.apache.org by "Stefan Gmeiner (JIRA)" <ib...@incubator.apache.org> on 2009/05/06 16:13:33 UTC
[jira] Created: (IBATIS-596) Null-References for sub selects with
lazy loading
Null-References for sub selects with lazy loading
-------------------------------------------------
Key: IBATIS-596
URL: https://issues.apache.org/jira/browse/IBATIS-596
Project: iBatis for Java
Issue Type: Improvement
Components: SQL Maps
Affects Versions: 2.3.4
Reporter: Stefan Gmeiner
We are using the iBatis enhanced (cglib) proxy for lazy loading our sub-select bean references.
Unfortunately if a reference is null iBatis creates a proxy with
null content. This makes using lazy loading less transparent to clients as they are required
to execute further checks to see if the returned object is null.
Hence we are suggesting a simple solution which is attached as a patch:
A proxy for a lazy loaded object is now only created if the foreign key is non-null.
When using the curly braces syntax (parameter map) a postfix '?' is required to activate
the new lazy loading otherwise the existing strategy is used. This allows for the possibility
of subselects requiring a null value as foreign key.
Example:
<result property="jobs" column="job_pk" select="selectJob"/>
This will return null if job_pk is null and a proxy for the job is job_pk is not null.
<result property="jobs" column="{transportIdentifier=job_pk}" select="selectJob"/>
This will always return a proxy object irrespective of the job_pk value.
<result property="jobs" column="{transportIdentifier=job_pk?}" select="selectJob"/>
This will return null if job_pk is null and a proxy for the job is job_pk is not null.
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[jira] Commented: (IBATIS-596) Null-References for sub selects with
lazy loading
Posted by "Kai Grabfelder (JIRA)" <ib...@incubator.apache.org>.
[ https://issues.apache.org/jira/browse/IBATIS-596?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12708538#action_12708538 ]
Kai Grabfelder commented on IBATIS-596:
---------------------------------------
Sounds like an interesting feature. Could you add a testcase against the current trunk? An updated iBATIS-SqlMaps-2_en.sxw file documenting your change would also be great.
> Null-References for sub selects with lazy loading
> -------------------------------------------------
>
> Key: IBATIS-596
> URL: https://issues.apache.org/jira/browse/IBATIS-596
> Project: iBatis for Java
> Issue Type: Improvement
> Components: SQL Maps
> Affects Versions: 2.3.4
> Reporter: Stefan Gmeiner
> Fix For: 2.3.5
>
> Attachments: null-proxy.patch
>
>
> We are using the iBatis enhanced (cglib) proxy for lazy loading our sub-select bean references.
> Unfortunately if a reference is null iBatis creates a proxy with
> null content. This makes using lazy loading less transparent to clients as they are required
> to execute further checks to see if the returned object is null.
> Hence we are suggesting a simple solution which is attached as a patch:
> A proxy for a lazy loaded object is now only created if the foreign key is non-null.
> When using the curly braces syntax (parameter map) a postfix '?' is required to activate
> the new lazy loading otherwise the existing strategy is used. This allows for the possibility
> of subselects requiring a null value as foreign key.
> Example:
> <result property="jobs" column="job_pk" select="selectJob"/>
> This will return null if job_pk is null and a proxy for the job is job_pk is not null.
> <result property="jobs" column="{transportIdentifier=job_pk}" select="selectJob"/>
> This will always return a proxy object irrespective of the job_pk value.
> <result property="jobs" column="{transportIdentifier=job_pk?}" select="selectJob"/>
> This will return null if job_pk is null and a proxy for the job is job_pk is not null.
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[jira] Commented: (IBATIS-596) Null-References for sub selects with
lazy loading
Posted by "Stefan Gmeiner (JIRA)" <ib...@incubator.apache.org>.
[ https://issues.apache.org/jira/browse/IBATIS-596?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12710370#action_12710370 ]
Stefan Gmeiner commented on IBATIS-596:
---------------------------------------
We found 2 more problems with lazy loading:
1. The Cglib-Proxy uses the parameter type instead of the result set type for creating a proxy object. This could be sometimes problematic if the client wants to casts from the parameter type to the result type. The attached file contains a test EnhancedLazyResultLoaderTest.testProxyType() for this problem and a patch to EnhancedLazyResultLoader.
2. If a proxy was created but not initialized and some times later the record for this proxy was deleted in the database all method calls to this proxy returns null. We think that this situation should be more explicit by throwing an exception in that case. See also the test WholePartTest.testDeletedLazyLoadedRelation() in the attached file.
> Null-References for sub selects with lazy loading
> -------------------------------------------------
>
> Key: IBATIS-596
> URL: https://issues.apache.org/jira/browse/IBATIS-596
> Project: iBatis for Java
> Issue Type: Improvement
> Components: SQL Maps
> Affects Versions: 2.3.4
> Reporter: Stefan Gmeiner
> Fix For: 2.3.5
>
> Attachments: null-proxy.patch, test-null-proxy.patch
>
>
> We are using the iBatis enhanced (cglib) proxy for lazy loading our sub-select bean references.
> Unfortunately if a reference is null iBatis creates a proxy with
> null content. This makes using lazy loading less transparent to clients as they are required
> to execute further checks to see if the returned object is null.
> Hence we are suggesting a simple solution which is attached as a patch:
> A proxy for a lazy loaded object is now only created if the foreign key is non-null.
> When using the curly braces syntax (parameter map) a postfix '?' is required to activate
> the new lazy loading otherwise the existing strategy is used. This allows for the possibility
> of subselects requiring a null value as foreign key.
> Example:
> <result property="jobs" column="job_pk" select="selectJob"/>
> This will return null if job_pk is null and a proxy for the job is job_pk is not null.
> <result property="jobs" column="{transportIdentifier=job_pk}" select="selectJob"/>
> This will always return a proxy object irrespective of the job_pk value.
> <result property="jobs" column="{transportIdentifier=job_pk?}" select="selectJob"/>
> This will return null if job_pk is null and a proxy for the job is job_pk is not null.
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