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How to avoid additional sql query for nested left join [message #1733983]

Thu, 02 June 2016 15:25

Pavel No

Messages: 47
Registered: May 2016

Member

I have the following entities:

@Entity
class A{
 @OneToMany
 private List<B> bs;
 ...
}

@Entity
class B{
 @OneToMany
 private List<C> cs;
 ...
}

@Entity
class C{
 ...
}

So I do the followin query:

SELECT a FROM A a LEFT JOIN FETCH a.bs b LEFT JOIN b.cs

This code works, the only problem that A and B are read from database in one join query, but for reading C (LEFT JOIN b.cs) separate sql query is executed to read only C entities. How to read A,B,C in one sql query.

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Re: How to avoid additional sql query for nested left join [message #1734850 is a reply to message #1733983]

Mon, 13 June 2016 13:46

Chris Delahunt

Messages: 1389
Registered: July 2009

Senior Member

JPQL doesn't support nesting fetch joins, so the only way to do this would be to use EclipseLink's "eclipselink.join-fetch" query hint: http://www.eclipse.org/eclipselink/documentation/2.5/jpa/extensions/q_join_fetch.htm

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