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From Jacek Żoch (JIRA) <j...@apache.org>
Subject [jira] Commented: (OPENJPA-450) Suboptimal Query strategy for JPA queries that return multiple Entities
Date Wed, 06 Aug 2008 09:40:45 GMT

    [ https://issues.apache.org/jira/browse/OPENJPA-450?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12620187#action_12620187
] 

Jacek Żoch commented on OPENJPA-450:
------------------------------------

I have the same problem. Is there any workaround known ?

> Suboptimal Query strategy for JPA queries that return multiple Entities
> -----------------------------------------------------------------------
>
>                 Key: OPENJPA-450
>                 URL: https://issues.apache.org/jira/browse/OPENJPA-450
>             Project: OpenJPA
>          Issue Type: Improvement
>          Components: query
>    Affects Versions: 1.0.1
>            Reporter: Nick Johnson
>            Priority: Minor
>         Attachments: openjpa_testcase.jar
>
>
> When a Query returns instances of  multiple Entity classes, the query strategy is suboptimal.
 First it issues a query to select all the primary keys, and then additional queries are issued
for every one of those primary keys.  If exactly one type of Entity is in the SELECT clause,
a much more efficient, single query is constructed.
> I'll attach a test case that demonstrates this.  Watch what happens when this:
> 		Query q = em.createQuery("Select message, article from Message message, Article article
 "
> is changed to this:
> 		Query q = em.createQuery("Select message from Message message, Article article  "
> in terms of which SQL statements are executed.
> FYI,  there's more detail on the users list with the subject, "how to avoid large number
of queries" and Patrick Linskey and I have emailed back and forth a bit about it.  I'm opening
this as a nicer way of keeping track of the issue.

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