On 2011-11-16, at 3:38 PM, David Avendasora wrote: > > On Nov 10, 2011, at 5:34 AM, Paul Hoadley wrote: > >> Say I have two entities, User and Role, and a joining entity UserRole to >> create a many-to-many relationship between them. So I have a relationship >> 'userRoles' from User to UserRole (and a relationship 'userRoles' from Role >> back to UserRole). I flatten the relationship on User, so I also have a >> 'roles' relationship on that entity. > > Wait. "Also"?!? That's insane. That's two distinct relationships representing > the same DB information, and one is hiding a huge piece of the action. You > are just asking for trouble.
I am hopeful that one of them is just in the model, you know, normal flattening through a join table? > Pick one. Get rid of the other. I vote for getting rid of the flattened > relationship. I find flattened relationships to be on the same level as > compound PKs. Sure they seem great, but eventually they come back to bite > you. They paint you into a long-term corner for short-term convenience sake. Except when hiding key only join tables. > Proper relationship molding seems simple, Yep, just get them damp and put them someplace warm and dark. > but it is full of subtleties and complexities and you can easily do things > that work fine in all but a few specific conditions and then they can corrupt > your data without you knowing it until it's too late. Having two > relationships that represent the same information makes database corruption > at least 10x more likely. > > Here's "Dave's Rules of Happy Modeling™" * > 1) No flattened relationships > 2) No compound primary keys > 3) One path to data (no cyclical relationships) No foo.bar.foo? What if you have a Foo and want the Bar? > 4) Model Inheritance only as the very last resort. Pfft. Use inheritance where is makes sense (Liskov sense, not for implementation or when you really want a Role). > *Oftentimes you are stuck with an existing/legacy DB and it is great that WO > gives you the tools to work with a sub-optimal (from an OO perspective) > architecture, but you should be very hesitant to use those tools when > creating a new architecture. True. But I want to hear more about relationship molding. I wonder if attributes would mold too.... Chuck -- Chuck Hill Senior Consultant / VP Development Practical WebObjects - for developers who want to increase their overall knowledge of WebObjects or who are trying to solve specific problems. http://www.global-village.net/products/practical_webobjects _______________________________________________ Do not post admin requests to the list. They will be ignored. Webobjects-dev mailing list (Webobjects-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/webobjects-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
