Hi Chuck, All the entities (A, B, C, and D) eventually have become IS-A relationship. I would also like to use interface instead of inheritance but thinking how I can manage the Entity E to have toOne relationship for all these entities using interface. May be I need to write custom code to manage the storage and retrieval for this relationship? Any clue or reference to existing example would be helpful.
Thanks, Farrukh Sent from my iPhone On 2010-11-07, at 1:00 AM, Chuck Hill <ch...@global-village.net> wrote: > If all they share is a few common, generic attributes, I would not use > inheritance for this. I'd prefer an interface. As Mark pointed out, > inheritance is for "IS A" relationships. It is not to save some > implementation time. That is an abuse of inheritance. If they share > behavior, then inheritance is more likely the correct design. > > Barbara Liskov has some excellent articles on this. Google for "Liskov > Substitution Principal". > > Chuck > > > On Nov 6, 2010, at 12:23 PM, Farrukh Ijaz wrote: > >> Yes, they will expose certain properties which are symmetrical in all the >> entities, e.g. title, description, etc. >> >> Consider this requirement as a tree structure which can have nodes that >> appear to be symmetric but their underlying user object can be different. >> >> Farrukh >> >> Sent from my iPhone >> >> On 2010-11-06, at 9:58 PM, Steve Peery <spe...@me.com> wrote: >> >>> Is there any shared functionality between Entity A, Entity B, Entity C and >>> Entity D that would justify Abstract Entity Alpha? >>> >>> Steve >>> >>> On Nov 6, 2010, at 7:39 AM, Farrukh Ijaz wrote: >>> >>>> Hi EOF-ologists, >>>> >>>> I've a modelling issue and need to know what could be the suitable fix (or >>>> tweak) to fulfil the requirement. >>>> >>>> Below is the existing EO Model. >>>> <Existing.png> >>>> I've two entities (Entity A and Entity B) extending Abstract Entity X but >>>> these entities have their own tables (no single table inheritance). I need >>>> to design Entity D and Entity E where Entity D has a toMany relationship >>>> with Entity E and Entity E needs to have a toOne relationship with Entity >>>> A, Entity B, Entity C and Entity D. >>>> >>>> 1. One way can be for Entity E to have four different relationships such >>>> as toEntityA, toEntityB, toEntityC and toEntityD. (This is _not_ desirable) >>>> 2. The other way mentioned in the lower diagram where Entity A, Entity B, >>>> Entity C and Entity D extend Abstract Entity X and Entity E will have >>>> toOne relationship with Abstract Entity X. (This is _desirable_). >>>> <Desired.png> >>>> What would be the easiest way to model such relationship? I'm _not_ >>>> relationship expert so may be the way I assumed the model (second diagram) >>>> can be wrong or practically impossible? >>>> Also note that I cannot make Entity C and Entity D to extend Abstract >>>> Entity X due to some design constraints therefore I think to introduce >>>> Abstract Entity Alpha. >>>> >>>> Thanks, >>>> >>>> Farrukh >>>> >>>> >>>> >>>> _______________________________________________ >>>> 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/speery%40me.com >>>> >>>> This email sent to spe...@me.com >>> >> _______________________________________________ >> 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/chill%40global-village.net >> >> This email sent to ch...@global-village.net > > -- > 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
