Hello! I'm experiencing some problems with HQL query productivity.
Current query looks like the following:


select new ObjectView(a.id, a.name, b, c)
from mypackage.B b
left outer join b.x x
left outer join x.c c
where b.objectId = ?


All domain objects are declared as lazy as well as collections. Currently, there are four queries being executed (log could be :

select from A;
select from B;
select from X
select from C;

I was trying to use fetch join in order to merge everything in one query:


select new ObjectView(a.id, a.name, b, c)
from mypackage.B b
left outer join fetch b.x x
left outer join fetch x.c c
where b.objectId = ?


But update query caused an error "query specified join fetching, but the owner of the fetched association was not present in the select list"
In "Hibernate3 Migration Guide" it mentioned, that furthermore, a query that specifies join fetching, but the owner of the fetched association was not present in the select list throws an exception now: "select b from A join fetch a.bees b" - this query makes no sense, remove the "fetch".

But the only object from the query that not present in select list is X, and fetching is exactly the target I'm trying to achieve.

Are there any solutions?

select new and join fetch doesn't really make sense.

Hello,

I am also trying to convert several queries to a single query using select new Object(args).

Previously, I retrieved a list of "Ccr" objects for viewing in a datatable on a JSF page. I then access the properties of these objects in each row of the table using syntax like #{ccr.property}. This works, but ends up requiring about five queries per row of the datatable when I could easily write it as one query for the whole table myself.

Here is the query I have come up with:



Each Ccr object has a collection called ccrAudits which contains CcrAudit objects. For each Ccr I would like to see the first and last CcrAudit, based on their timestamps. Sometimes the first and last might be the same.

However when this query is run, only the id fields for the three objects in the constructor of the new object are retrieved, and all other information is loaded after that in even more queries than before. I thought it might be that I am aliasing a collection (with one object in it) to a single object in the constructor, but hibernate doesn't seem to mind that and changing the query to a restricted cartesian product doesn't make any difference to the number of queries being run.

I also tried fetch joining as in the manual, but got the following error message:



Any suggestions would be greatly appreciated,
Dave

I am doing some volunteer work for the local school district, and they use Hibernate.

I am also getting the following from a query:

I am trying to run a report on the number of broadcasts the district makes in a month:



The query gives the exception stated above. If I only have Broadcast in the from clause and have no where clause the query works. But we want to limit the query to only broadcasts on public channels which is two tables over.

In the DAO classes, they use get() when retrieving an single entity because they don't want the object to load lazy, and fetch="join" in the XML for the relationships to avoid the n + 1 query problem. Since fetch="join" in the XML is ignored for HQL queries, we use left join fetch in the HQL.

Since the person above mentioned that "select new and join fetch doesn't really make sense", what other options would there be for this scenario where we need the join fetch for the where clause?

Am I missing something obvious?

Thanks!

The fetch keyword tells hibernate to eager load the association which does not make sense as you are not loading the parent object itself but instantiating a new object from its values.

It can does not make sense, but im some cases if I don´t use the fetch keyword the object comes lazy im my class constructor. Can it be a mapping problem?