Joined subclass and primary foreign keys

tsouza · **Joined:** Sun Feb 08, 2004 4:09 pm **Posts:** 46

Hi ppl,

I understand that, in a <joind-subclass>, the <key> property identifies the joined column, but what about primary foreign keys? Can i use <id> or <composite-id> right after the <key> tag?

Cya!
Thiago Souza

emmanuel · **Posted:** Wed Feb 11, 2004 8:01 am

The id is stored in the parent class and thus in the parent table.
It's inconsistent to store an id in <subclasses> or <joined-subclasses>

tsouza · **Joined:** Sun Feb 08, 2004 4:09 pm **Posts:** 46

Ok, but i'm talking about FOREIGN keys... i know that the primary key is generated in parent tables, but I wanna know about foreign keys that should be primary keys... got it?

emmanuel · **Posted:** Wed Feb 11, 2004 9:55 am

<key> and key colum(s) is a pure technical stuff.

If you want this column to be involved in a many-to-one, then add insert="false" update="false".

I don't understand "foreign keys that should be primary keys".

tsouza · **Joined:** Sun Feb 08, 2004 4:09 pm **Posts:** 46

It's primary foreign key! They are foreign keys that are grouped in primary keys! As in identifying relashionship in relational database...

tsouza · **Joined:** Sun Feb 08, 2004 4:09 pm **Posts:** 46

My problem is that I have an identifying relationship in a subclass... so, as it is a subclass, it has and id (used to make the joins in the superclasses), but i have primary foreing keys that comes from the identifying relationship, if it were UNidentifying, ok, I would have a normal collection, but it isn't, the foreign key should be primary foreign key...

emmanuel · **Posted:** Wed Feb 11, 2004 12:35 pm

All right I give up. Maybe a native english user will understand.

tsouza · **Joined:** Sun Feb 08, 2004 4:09 pm **Posts:** 46

tsouza · **Joined:** Sun Feb 08, 2004 4:09 pm **Posts:** 46

So... how I would map Table B if it has the joiner key column AND a primary foreign key...

michael · **Posted:** Wed Feb 11, 2004 5:36 pm

I don't know what you mean with "partitioning" and "identifying relationship", but as far as I understand you you could simply map this with a relationship tag (one-to-one or many-to-one or such) inside the joined-subclass mapping.

tsouza · **Joined:** Sun Feb 08, 2004 4:09 pm **Posts:** 46

Ok, I understand this... but, shouldn't I need to map somewhere that the column in the <many-to-one> is a primary key in the database?

greg_barton · **Posted:** Wed Feb 11, 2004 6:26 pm

No.

(I'm a native english speaker and I'm having a hard time too. :P )

greg_barton · **Posted:** Wed Feb 11, 2004 6:31 pm

Code:

<hibernate-mapping> 

    <class name="DataObject" table="data_objects">

        <id name="id" type="long">
            <generator class="native"/>
        </id>
        
        <joined-subclass name="Movie" table="movies">
                    
            <key column="id"/>
            
            <many-to-one name="trailer" class="MovieTrailer"/>
        
        </joined-subclass> 
        
        <joined-subclass name="MovieTrailer" table="trailers">
                
            <key column="id"/>
            
        </joined-subclass> 
        
    </class>
    
</hibernate-mapping>

michael · **Posted:** Wed Feb 11, 2004 6:37 pm

Ah, Greg, the master of examples :) Thanks.

tsouza · **Joined:** Sun Feb 08, 2004 4:09 pm **Posts:** 46

Ok! Thanks! But those terms "partitioning" and "identifying relationships" I learned in university and I have seeing it in a lot of database design tools... you ppl should know them =)

But thanks for tha help!