I am new to OJB but have some input. I could be smoking something, so be warned...
If Product can only be associated with one Group, shouldn't one assume you would be referring to the Group using it's unique identity (primary key)? How else can you guarantee effeciency and uniqueness? In the Collection case, it makes sense to support a field name, as now the assumption is there are N members in the set, not one. As for more arbitrary join scenarios, you are getting at rub of the whole OO/Relational problem. There are generally a number of strategies, including explicit definition of N..M relationships, query by navigation or filtering (expensive!), explicit denormalization, or straight SQL/reporting. > -----Original Message----- > From: David Mitchell [mailto:[EMAIL PROTECTED]] > Sent: Thursday, February 13, 2003 11:57 AM > To: 'OJB Users List' > Subject: RE: foreign keys... again, joins, and OJB templates > > > > Im having the same issue exactly, and was trying to figure > out how to put > the question! > > I have two tables, Product and Group. A product can only be > in one group, > but a group has many products. Here are representative schemas: > > table Product > ndx int primary key, > name varchar, > code varchar, > groupNdx int > > table Group > ndx int primary key, > name varchar, > code varchar > > So, im joining Product.groupNdx with Group.ndx. As I > understand it, in the > schema definition for Product, you provide a reference > descriptor for the > link to group, "groupNdx". > > Im guessing, what happens is that groupNdx is matched with > whatever the > primary key is on Group, since we've said it refers to the > group class in > our reference descriptor. > > But what if you're not joining on a primary key? > > I see that in the torque schema, it very clearly indicates > the local field > name and foreign field name in foreign key relationship definitions. > > Similarly, in the OJB repository, for collections, there is > a similar way > to provide that foreign field name. But not for reference > descriptors..? Is > it just an oversight? > > Finally, what if you're not joining on primary keys at all? > What if I want > to say "give me all the names of pieces of art, that share an > employee's > first name?" > > In torque, it looks like they have addJoin() methods for > criteria, so you > can link two arbirarily columns in two arbitary tables. How > come this doesnt > exist for the OJB queries? > > Oh, one last thing, one request is if the sql, jdbc, ojb-model, and > ojb-repository build targets and templates could be brought > into the OJB > file structure and a "ready to customize for your app ant > script" rather > than being hardcoded in the torque jarfile... This would > allow us (as in the > OJB community, rather than the torque community) to take over > maintenance of > the ojb-related templates if nothing else. > > yours, > David Mitchell > > > > -----Original Message----- > From: Robert S. Sfeir [mailto:[EMAIL PROTECTED]] > Sent: Thursday, February 13, 2003 10:34 AM > To: oJB List > Subject: foreign keys... again > > > Still a bit confused, If I have this: > > <class-descriptor class="net.sfeir.business.RequestBO" > table="REQUESTS"> > <field-descriptor name="assignedToID" column="assignedTo" > jdbc-type="INTEGER"/> > ... > > and I want to setup a foreign key from assignedToID to another table > called Users and the column there is called userID > I added this as the foreign-key reference: > > <reference-descriptor name="userBO" > class-ref="net.sfeir.security.business.UserBO"> > <foreignkey field-ref="userID"/> > </reference-descriptor> > > But it doesn't make any sense, if I put assignedToID in the > field-ref, > how does it know the column I am mapping? If I put the userID like I > did in the field-ref how does it know that I am mapping > assignedToID? > You can't always expect the table column names to match, most of the > time they won't. > > I'm missing something here that would let me tell the descriptiptor. > The RequestBO object has a getter and setter which get back a > UserBO as > suggested earlier, but even if it does a getUserBO() and it gets the > UserBO back, UserBO doesn't have a method called > getAssignedTOID() nor > do I want to do that because that's breaking the OO rules of the > framework. > > I'm totally confused right now and unfortunately, the docs > are not very > clear. > > > R > > -- > Robert S. Sfeir > Senior Java Engineer > National Institutes of Health > Center for Information Technology > Department of Enterprise Custom Applications > [EMAIL PROTECTED] > > > --------------------------------------------------------------------- > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > > > +---------------------------------------------------------+ > This message may contain confidential and/or privileged > information. If you > are not the addressee or authorized to receive this for the > addressee, you > must not use, copy, disclose or take any action based on this > message or any > information herein. 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