Hello everybody,

I have the following problem:

There is a parent class (let's name it "PARENT") which has a one-to-many relationship to a child class (let's name such a class as "CHILD"). So, a PARENT instance contains a Collection with CHILDs (let's name the collection class property as "childs").

Such a collection is specified in the Hibermnate-config file for PARENT like the following:


A PARENT may have no CHILDs such that there is no corresponding rows in the CHILD-related DB table at all or there are some rows, but they are not considrered because of 'WHERE' in the mapping.

I need to produce an HQL query which will return in each result "row" some details about a PARENT along with details of a corresponding CHILD (if any). Logically, a LEFT JOIN is a solution. Something like:


But the 'WHERE' in the mapping prevents such a LEFT JOIN: if no CHILDs exists for a PARENT (taking the 'WHERE' into consideration), then nothing is returned (not just 'NULL' in place of 'ch.key'). I know such a "WHERE-influenced" logic for HQL joins, so it looks like not an extraordinary thing.

But I would need to write a query which delivers NULLs in place of CHILDs data if it does not exist. The WHERE condition can not be eliminated from mapping. Are there any ways to get what I want?

Thanks in advance,
Andrew

I have the same problem. I'm new to hibernate as of a couple days ago.

I'm using a regular SQL query instead of a HQL query.

The only problem is that I can't get the results out of q.list(). It keeps telling me the object cannot be cast.

Basically, what I want to do is create a join that automatically populates the children in the parent class if they exist. For example, my parent class has a "public Set getChildren()" method that lazy loads the children when called. I want to create X parent class instances and pre-load that Set with children(if they exist) using a left join.

Matt

But I need an HQL query, no SQL...

I almost have it using HQL

The basic part of my query is this. The key is the "fetch" keyword.



That seems to have populated the classes but in a strange way. Every parent gets all the children, even if they are not related by the join. The query executed by Hibernate manually returns the correct results, in my case 4 rows. But when I do something like this:




It would print something like


When the real relationship is

I fixed from something I found in the faq. It doesn't seem right though. The query returns 4 rows, yet when I print it out, its 13 rows.

I added this:


That works but, with the possibility of thousands of rows being returned, how long is it going to take it to filter out the duplicates that it seems to create on its own?

Nm, I see why. Every row is a join between the child and parent, so you have duplicate references to the same parent.

This should work: