[jira] Commented: (CAY-1025) Do something about to-many prefetch limitations

["Andrus Adamchik (JIRA)" <de...@cayenne.apache.org>]

    [ https://issues.apache.org/cayenne/browse/CAY-1025?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13180#action_13180 ] 

Andrus Adamchik commented on CAY-1025:
--------------------------------------

Implemented a switch to joint prefetch on a local branch. Also implemented a related CAY-1128.

TODO:

1. need to test performance (e.g. vs 3.0M4 of the two solutions)
2. Some tests are still failing. There seem to be a number of unaddressed JOINT prefetch limitations.


> Do something about to-many prefetch limitations
> -----------------------------------------------
>
>                 Key: CAY-1025
>                 URL: https://issues.apache.org/cayenne/browse/CAY-1025
>             Project: Cayenne
>          Issue Type: Improvement
>          Components: Cayenne Core Library
>    Affects Versions: 1.2 [STABLE], 2.0 [STABLE], 3.0
>            Reporter: Andrus Adamchik
>            Assignee: Andrus Adamchik
>             Fix For: 3.0
>
>
> http://cayenne.apache.org/doc/prefetching.html
> "PREFETCH LIMITATION: To-many relationships should not be prefetched if a query qualifier can potentially reduce a number of related objects, resulting in incorrect relationship list."
> This can bite an unsuspecting user... So we either 
> 1. Address the core limitation by building a correct prefetch query (use subselect?)
> 2. Detect these cases and throw an exception
> 3. Detect these cases and silently drop a prefetch
> I should note that debugging these problems is very hard, as they look totally random until you get to the cause.

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