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Eager OneToOne relationship not using JOIN [message #653898] Fri, 11 February 2011 13:16 Go to next message
Mauro Flores is currently offline Mauro Flores
Messages: 83
Registered: September 2009
Location: Brasil
Member
An entity A has an eager one to one relationship with B(ore many to one).

When I run "Select a FROM A a", I'd like to eclipselink build just one sql select clause with a A e B joined.

But, unfortunally, eclipslinks build many sql select clause. One for listing A, and for each A instance a sql select for B.

How can I configure eclipselink in order to buld just one select clause?

Thanks. Mauro

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Re: Eager OneToOne relationship not using JOIN [message #653901 is a reply to message #653898] Fri, 11 February 2011 13:31 Go to previous messageGo to next message
Chris Delahunt is currently offline Chris Delahunt
Messages: 862
Registered: July 2009
Senior Member
Hello Mauro,

You can add a fetch join into the JPQL:
"Select a FROM A a left join fetch a.b"
You can also use a query hint or set the mapping to always join using the @JoinFetch Annotation described here:
http://wiki.eclipse.org/Optimizing_the_EclipseLink_Applicati on_(ELUG)#How_to_Use_Batch_and_Join_Reading_for_Optimization

Best Regards,
Chris

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Re: Eager OneToOne relationship not using JOIN [message #653908 is a reply to message #653898] Fri, 11 February 2011 15:01 Go to previous message
Mauro Flores is currently offline Mauro Flores
Messages: 83
Registered: September 2009
Location: Brasil
Member
Thanks, Chris. I didn't know that.

But, why do I need to explicitally say that I want a join in this case?
In my oppinion the default should be the faster implementation.
One select with a left join would always be faster than many selects.

That's the behaviour of openjpa implementation.

Is there a property in persistence.xml to make the left join default for all application?

Thanks.




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