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From "Patrick Linskey" <plins...@bea.com>
Subject RE: extraneous joins OPENJPA-134
Date Thu, 15 Feb 2007 00:05:27 GMT
What if just one side is eager? Also, is the @OneToMany's mappedBy
attribute set up correctly?

-Patrick

-- 
Patrick Linskey
BEA Systems, Inc. 

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> -----Original Message-----
> From: David Wisneski [mailto:wisneskid@gmail.com] 
> Sent: Wednesday, February 14, 2007 3:27 PM
> To: open-jpa-dev
> Subject: extraneous joins OPENJPA-134
> 
> Hi Patrick or Abe,
> 
> I was wondering if any of you have noticed the following problem.  (
> this is written up as OPENJPA-134).  This shows up as a performance
> problem in applications when we compare with  Hibernate.
> 
> If I have a M:1 relationship and I make both sides of the relationship
> EAGER in the mapping, OR  I do a  join fetch of the multi side
> relationship,  we see an extra join in the generated sql.
> 
> Example:  I have a Dept -> Emp with inverse Emp->Dept.
>  If both sides are EAGER in mapping I get the sql
> 
>   select ..  from dept t0 join emp t1 on(...) join dept t2 on (...)
> 
>  If both sides are LAZY and I do EJB query
>   select  d from Dept d left join fetch d.emps
> 
> the generated sql is
>   select ...  from dept t0 left join emp t1 on(...) join dept 
> t2 on(...)
> 
> The extra  "join dept t2 on(...)" seems to be extraneous and has a
> serious impact on performance.   Since I already joined Dept with Emp,
> there is no need to join it back to the Dept because the Dept->Emp and
> Emp->Dept relationships are inverses of the same foreign key.
> 
> Have you noticed this same problem?  Might you have a quick fix that
> you can?  Otherwise we will start analyzing to see what might be
> causing it.
> 

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