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From Andrus Adamchik <and...@objectstyle.org>
Subject Fwd: [jira] [Closed] (CAY-1695) Unexpected null value in bidirectional one-to-one prefetch
Date Thu, 11 Jul 2013 15:33:57 GMT
FYI .. this fix significantly changed the algorithm for refreshing prefetched objects. When
processing a prefetch tree of objects, and looking at a given object, the new algorithm checks
object's "snapshotVersion", and if it is >= than the version of the first DataRow in the
current transaction, it skips the object refresh (assuming it was already refreshed in this
tx). 

Aside from fixing "circular" prefetches, this also improves processing performance in some
cases where we've already tracked processed objects (only via a separate HashMap).

But now I am worrying that I overlooked something in my assumptions. 

I can think of a few hypothetical future scenarios when this might break if we change this
or that piece. E.g. "version of the first DataRow in the current transaction" may not really
be the first if we ever change processing flow of a query. Or if we lift synchronization of
updates from other contexts and start getting updates from parallel transactions. 

Can't think of any scenario that might break the current stack. This doesn't mean it does
not exist :) So this is a call to early adopters who are running trunk builds - please give
us feedback on this feature! When you use prefetching and see some objects not being refreshed,
let's analyze your query and see if this change is to blame. 

Thanks,
Andrus


 
Begin forwarded message:
> From: "Andrus Adamchik (JIRA)" <jira@apache.org>
> Subject: [jira] [Closed] (CAY-1695) Unexpected null value in bidirectional one-to-one
prefetch
> Date: July 10, 2013 6:41:49 PM GMT+03:00
> To: commits@cayenne.apache.org
> Reply-To: dev@cayenne.apache.org
> 
> 
>     [ https://issues.apache.org/jira/browse/CAY-1695?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
> 
> Andrus Adamchik closed CAY-1695.
> --------------------------------
> 
>       Resolution: Fixed
>    Fix Version/s:     (was: 3.2M1)
>                   3.2M2
> 
> Fixed for the attached unit test. The strategy used here is to grab the lowest version
of the data row in a given transaction and use it as a marker to check against object versions.
When creating an object, if we detect that it was already processed in this tx, we skip its
processing.
> 
>> Unexpected null value in bidirectional one-to-one prefetch
>> ----------------------------------------------------------
>> 
>>                Key: CAY-1695
>>                URL: https://issues.apache.org/jira/browse/CAY-1695
>>            Project: Cayenne
>>         Issue Type: Bug
>>         Components: Core Library
>>   Affects Versions: 3.1M3
>>           Reporter: Andrei Veprev
>>            Fix For: 3.2M2
>> 
>>        Attachments: 0001-CAY-1695-Unexpected-null-value-in-bidirectional-one-.patch,
CAY-1695-test.patch
>> 
>> 
>> For example you have User and UserInfo entities. User has one-to-one relationship
with UserInfo. If you try to do select for User with prefetching on userInfo and userInfo.user,
you will get null value for userInfo property:
>> SelectQuery query = new SelectQuery(User.class);
>> query.addPrefetch("userInfo");
>> query.addPrefetch("userInfo.user");
>> It doest meter which kind of prefetching do you use. 
> 
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