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Left outer join on a unidirectional many to one mapping [message #518116]

Wed, 03 March 2010 02:08

Eclipse User

I have a many to one relationship from object A to object B.

When I use a bidirectional mapping I can executed the following JPQL query:

SELECT b, a FROM B b LEFT OUTER JOIN b.a a

How can I achieve the same result if I have a unidirectional mapping?

I know it can be done in SQL but I would like to implement it in JPQL.

Thanks,
Andreas

Re: Left outer join on a unidirectional many to one mapping [message #518587 is a reply to message #518116]

Thu, 04 March 2010 09:56

Eclipse User

Maybe,

"Select b, a from A a left join a.b b"

or,
"Select b, a from B b, A a where a.b = b"

Re: Left outer join on a unidirectional many to one mapping [message #519188 is a reply to message #518587]

Sun, 07 March 2010 16:07

Eclipse User

The first query is the opposite of what I want. It will give all rows of A and information from B if the relationship is set.

The second query does the same thing but with a different notation.

Would it help if I posted my actual mappings and query?

Re: Left outer join on a unidirectional many to one mapping [message #519191 is a reply to message #518116]

Sun, 07 March 2010 16:52

Eclipse User

Here is the outer join I want to perform in native SQL:

SELECT a.*, b* FROM A a LEFT OUTER JOIN B b ON (b.aID = a.ID);

Re: Left outer join on a unidirectional many to one mapping [message #519383 is a reply to message #518116]

Mon, 08 March 2010 11:52

Eclipse User

That is what,

"Select b, a from A a left join a.b b"

would generate? I assume you want "B b LEFT OUTER JOIN A a" though.

I guess there is no way to do this in JPA without adding the bidirectional relationship, or using native SQL.

In EclipseLink, you can add a OneToOneQueryKey that allows you to define a relationship without having a mapping for it. You can then use the query key in EclipseLink Expression queries. Unfortunately, query keys are not currently supported in JPQL queries (please log a bug for this and vote for it).

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