HQL: How to display super and sub-class columns in one query

anagna · **Joined:** Fri Sep 08, 2006 9:55 am **Posts:** 2

Hibernate version: 3.1

My question is, how can I in the same HQL query (and given that HQL doesn't support UNIONs), select columns from both a parent class and its sub-classes, and have nulls appear for subclass fields when dealing with rows of the base class.

For example, I have
- class Baseclass with field baseclass1
- class Subclass with field subclass1, with Subclass deriving from Baseclass

and I want in my query to select all instances of both Subclass & Baseclass, and:
- When dealing with an object of type Subclass, then show fields baseclass1 and subclass1

- When dealing with an object of type Baseclass, then show fields baseclass1 and null

The LEFT OUTER JOIN doesn't work with Base-Subclass constructs, so it can't be used in this case.

pasha · **Joined:** Sat Nov 27, 2004 4:13 am **Posts:** 137

query: from pkg.Parent

well, the query returns all parent and subclass instances!

and then check them by: instanceof

anagna · **Joined:** Fri Sep 08, 2006 9:55 am **Posts:** 2

In my case, I'm not looking for objects but directly for column values. I need to populate a grid based on the result, and the whole point is to avoid writing code and simply have an HQL query in a configuration file driving the grid contents.

pasha · **Joined:** Sat Nov 27, 2004 4:13 am **Posts:** 137

well do something like:

Code:

select new Child(p.id, p.f1, p.f2, c.f1, c.f2)
from Parent as p outer join Child as c on p.id = c.id

by the way, I don't like it!

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