结合两个HQL查询

Question

I have two entities with the following fields:

Application: applicationId, name, description, lastVersion (transient)

and

ApplicationVersion: applicationVersionId, application, versionName, creationDate

I'm trying to get a Collection with all applications and, for the applications with one or more version, put the versionName of the ApplicationVersion with the most recent creationDate in the transient field lastVersion.

At this moment i'm doing this with two hql queries:

This one to get all the unversioned applications:

SELECT a from Application a where a not in (select b.application from ApplicationVersion b)

And this to get the last version of the versioned ones:

select b from ApplicationVersion b where b.creationDate = (select max(bb.creationDate) from ApplicationVersion bb where bb.application = b.application)

After executing both, I iterate over the second resultset and add this applications and their last eversion to the first resulset.

But I want to combinate both queries in something like this (this is not working at all):

select new foo.bar.Application(a.applicationId, a.name, a.description, b.version) from Application a, ApplicationVersion b where 
(a not in (select bb.application from ApplicationVersion bb)) 
or 
(a=b.application and b.creationDate = (select max(bb.creationDate) from ApplicationVersion bb where bb.application = b.application))

Is there any (efficient) way to combinate both queries and execute only one, and avoid do the iteration programmatically?

Answer 1

Yes, you could make it better, when your children records have a parent, you have to use

join fetch 

for example, you have Application, and ApplicationVersion, then:

from ApplicationVersion av
join fetch av.application ap
where ap.applicationId = :id

With this way, you have a relation between both objects and you can filter using where expression, be sure your ApplicationVersion has an attribute referencing Application object.

Hope it helps to you.