HQL queries and polymorphism

yyop · **Joined:** Wed May 25, 2005 10:37 am **Posts:** 5

Hi, I am running into a problem when using HQL (or Criteria API) with Hibernate 3, I've been reading some of the posts but I am not sure yet if it's possible to do what I want.

The question is, given the next mapping:

Code:

<class 
    name="A"
    table="values"
    lazy="false">

    ...

    <subclass
        name="B"
        discriminator-value="1">

        <property name="value" type="string">
            <column name="string_value" sql-type="text"/>
        </property>
        
    </subclass>
    
    <subclass
        name="C"
        discriminator-value="2">

        <property name="value" type="double">
            <column name="number_value" />
        </property>
    </subclass>
    
</class>

and the next classes:

Code:

public abstract class A {
    public abstract Object getValue();
    public abstract void setValue(Object obj);
}

public class B extends A {
    private String value;
    public Object getValue() {
        return value;
    }
    public voud setValue(Object obj) {
        this.value = (String) obj;
    }
}

public class C extends A {
    private Integer value;
    public Object getValue() {
        return value;
    }
    public voud setValue(Object obj) {
        this.value = (Integer) obj;
    }
}

Is it possible to execute polymorphic HQL queries such as the next ones?:

Code:

from A as a where a.class = B and a.value = 'test'      // It should check the string_value field

from A as a where a.class = C and a.value = 1           // It should check the number_value field

In my tests Hibernate doesn't seem "smart" enough to choose the right field of the table, but maybe I am doing something wrong or it's simply not possible.

Could anyone give me any clue about this?

Thanks![/code]

yyop · **Joined:** Wed May 25, 2005 10:37 am **Posts:** 5

I have implemented a workaround using SQL and criteria API, but is not very nice though.

Is the HQL stuff definitely not supported by the current version?

Thanks!

marco-p · **Posted:** Thu May 26, 2005 10:13 am

Why you dont' simply use:

Code:

from B as b where b.value = 'test'

and

from C as c where c.value = 1

Instead of specify the class instance as a where clause, simply use it in the from. You can always up-cast the result to A.

Kango · **Joined:** Sun Jun 13, 2004 9:49 pm **Posts:** 38

Any more comments on this one.

I'm running into the same problem but cannot use the from B or from C as marco suggested.

A user types a product name into a text box and i'd like to look up the record, but i don't know what type it is.

So, i want to do from A where a.blah = "what the user typed".

Is this possible yet?

sodamnmad · **Joined:** Wed Feb 08, 2006 11:40 pm **Posts:** 8

I've got a similar problem in that 2 subclasses (B anc C) of A have a field with the same name and same type (string). When I do a criteria search, the hql shows that its searching for the common field only in B. In other words, I get something like this:

... where (B.common like ?) or (B.common like ?)

This is sort of a bug because I need it to be:

... where (B.common like ?) or (C.common like ?)

It works properly for fields that don't have the name across B and C. It seems that the problem can easily be fixed by allowing the classname to be given along with the field name when creating the expression.

I'm generating a generic search using refelction and the line that does the actual work is:

disj.add(Expression.like(fld, sToken, MatchMode.ANYWHERE));

From this point, it would be very easy for me to include the class to search in (so that I can tell it to search in B.common and C.common as needed. Is there a way to do this? There is a chance I've overlooked this.

ps. Don't ask why the common field isn't moved to the superclass, its not my decision to make.