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Re: [eclipselink-users] Outer joined one-to-many question 
Should be something like:
"SELECT e FROM Employee e LEFT OUTER JOIN e.projects projects WHERE (e.projects IS EMPTY OR EXISTS(SELECT p FROM Project p WHERE (p IN(e.projects) AND p.name LIKE 'A%')))" 


On 8/19/2013 1:24 PM, Laird Nelson wrote:

I have a parent entity with an optional one-to-many relationship with a
child entity.

I am using LEFT OUTER JOIN in a query on the child entity.

The relevant excerpt from my query looks like this:

SELECT p.id <http://p.id>
   FROM Parent i
   LEFT OUTER JOIN i.children child

If I want to end up returning a p.id <http://p.id>object even when
elements in that p.children relationship are not present--i.e. because
the LEFT OUTER JOINdidn't find any related objects--how would I check
for this?

I had something like this (this is the relevant fragment from the
WHEREclause):

    AND (child IS NULL OR child.somethingOrAnother = 'someValue'...

When I do this, I get the following exception/warning in the logs:

Exception [EclipseLink-6076] (Eclipse Persistence Services -
2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.QueryException
Exception Description: Object comparisons can only be used with
OneToOneMappings.  Other mapping comparisons must be done through query
keys or direct attribute level comparisons.
Mapping: [org.eclipse.persistence.mappings.OneToManyMapping[children]]

To me, this looks like I can't really use "child" directly--as I am
doing in that WHEREclause fragment.  Should I be doing something like:

    AND (IS EMPTY(child) OR child.somethingOrAnother = 'someValue'...

...instead?

Thanks,
Best,
Laird

--
http://about.me/lairdnelson


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