Hello, Suppose I have 2 models Human and Person and I want to inherit one from another so that I could use ''human'' model/migration as a generic builder for smiliar objects as ''person'', for instance this with the following table structure: human table: id weight size person table: id name surname address Is it possible to make such table inheritance in rails to be able to have ''base'' model for those that are submodels with different columns? Thanks in advance! -- Posted via http://www.ruby-forum.com/.
On Thu, Nov 5, 2009 at 4:23 PM, Aljaz Fajmut < rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:> > Hello, > > Suppose I have 2 models Human and Person and I want to inherit one from > another so that I could use ''human'' model/migration as a generic builder > for smiliar objects as ''person'', for instance this with the following > table structure: > > human table: > id > weight > size > > person table: > id > name > surname > address > > Is it possible to make such table inheritance in rails to be able to > have ''base'' model for those that are submodels with different columns? > > Thanks in advance! >Yes, this is possible in Rails. Thus, you can read section 19.4 of AWDwR 3rd edition. It provides an excellent example of what one would do to achieve table inheritance in Rails. Good luck, -Conrad> -- > Posted via http://www.ruby-forum.com/. > > > >--~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
Aljaz Fajmut wrote:> Hello, > > Suppose I have 2 models Human and Person and I want to inherit one from > another so that I could use ''human'' model/migration as a generic builder > for smiliar objects as ''person'',Your data modeling is faulty. Human is not a sub- or superclass of Person; rather, they''re near synonyms.> for instance this with the following > table structure: > > human table: > id > weight > size > > person table: > id > name > surname > addressWhere''s the inheritance here? There are no fields in common except id. What do you actually want to do?> > Is it possible to make such table inheritance in rails to be able to > have ''base'' model for those that are submodels with different columns? >Well, there''s single-table inheritance (see the Rails docs), but it''s seldom a good idea...> Thanks in advance!Best, -- Marnen Laibow-Koser http://www.marnen.org marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org -- Posted via http://www.ruby-forum.com/.
It might not be the best example but I couldnt think of better one in the moment in wrote this. I have a clear image of what I want to implement. Is this single or multi-table inheritance? Thanks for help Marnen Laibow-Koser wrote:> Aljaz Fajmut wrote: >> Hello, >> >> Suppose I have 2 models Human and Person and I want to inherit one from >> another so that I could use ''human'' model/migration as a generic builder >> for smiliar objects as ''person'', > > Your data modeling is faulty. Human is not a sub- or superclass of > Person; rather, they''re near synonyms. > >> for instance this with the following >> table structure: >> >> human table: >> id >> weight >> size >> >> person table: >> id >> name >> surname >> address > > Where''s the inheritance here? There are no fields in common except id. > What do you actually want to do? > >> >> Is it possible to make such table inheritance in rails to be able to >> have ''base'' model for those that are submodels with different columns? >> > > Well, there''s single-table inheritance (see the Rails docs), but it''s > seldom a good idea... > >> Thanks in advance! > > Best, > -- > Marnen Laibow-Koser > http://www.marnen.org > marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org-- Posted via http://www.ruby-forum.com/.
Aljaz Fajmut wrote:> It might not be the best example but I couldnt think of better one in > the moment in wrote this. I have a clear image of what I want to > implement.Then you should be able to explain it more clearly. :)> > Is this single or multi-table inheritance?They''re functionally more or less equivalent, although single-table inheritance is rather a perversion of the relational model. The choice between the two usually seems to be made on practical grounds.> > Thanks for help > >Best, -- Marnen Laibow-Koser http://www.marnen.org marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org -- Posted via http://www.ruby-forum.com/.
Ok - I might be complicating too much. Heres how I would do it with c++, not 100% sure what approach should I take with rails on the database/model level. If I want to have generic data-storage model Vehicle (which will hold information the same information for all the vehicles - car, boat, etc.) class vehicle holds: color, max-speed, .. class car: color, max-speed, number of seats, .. class boat: color, max-speed, ... with some boat-specific columns I''d just derive car from vehicle and use car-specific data columns because similar operations will be called on it as on boat model. As far as I understand RoR approach: if I have a lot of duplicated code in my application, there must be some better solution for my problem. What do you think? Marnen Laibow-Koser wrote:> Aljaz Fajmut wrote: >> It might not be the best example but I couldnt think of better one in >> the moment in wrote this. I have a clear image of what I want to >> implement. > > Then you should be able to explain it more clearly. :) > >> >> Is this single or multi-table inheritance? > > They''re functionally more or less equivalent, although single-table > inheritance is rather a perversion of the relational model. The choice > between the two usually seems to be made on practical grounds. >> >> Thanks for help >> >> > > Best, > -- > Marnen Laibow-Koser > http://www.marnen.org > marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org-- Posted via http://www.ruby-forum.com/.
On Thu, Nov 5, 2009 at 5:44 PM, Aljaz Fajmut < rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:> > It might not be the best example but I couldnt think of better one in > the moment in wrote this. I have a clear image of what I want to > implement. > > Is this single or multi-table inheritance? > >You can implement this as single table inheritance because a RDBMS doesn''t support multi-table inheritance (i.e.one cannot inherit the fields of another table). If this is what you''re looking for, then you''ll need an OODB which represents things as object graphs instead of table rows. Lastly, Marnen is correct in saying that Person and Human are synonyms of one another and I recommend reading up on object oriented design. Good luck, -Conrad> Thanks for help > > Marnen Laibow-Koser wrote: > > Aljaz Fajmut wrote: > >> Hello, > >> > >> Suppose I have 2 models Human and Person and I want to inherit one from > >> another so that I could use ''human'' model/migration as a generic builder > >> for smiliar objects as ''person'', > > > > Your data modeling is faulty. Human is not a sub- or superclass of > > Person; rather, they''re near synonyms. > > > >> for instance this with the following > >> table structure: > >> > >> human table: > >> id > >> weight > >> size > >> > >> person table: > >> id > >> name > >> surname > >> address > > > > Where''s the inheritance here? There are no fields in common except id. > > What do you actually want to do? > > > >> > >> Is it possible to make such table inheritance in rails to be able to > >> have ''base'' model for those that are submodels with different columns? > >> > > > > Well, there''s single-table inheritance (see the Rails docs), but it''s > > seldom a good idea... > > > >> Thanks in advance! > > > > Best, > > -- > > Marnen Laibow-Koser > > http://www.marnen.org > > marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org > > -- > Posted via http://www.ruby-forum.com/. > > > >--~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
On Fri, Nov 06, 2009 at 01:23:25AM +0100, Aljaz Fajmut wrote:> human table: id weight size > person table: id name surname addressIf I understand your question correctly, you need to build the right relationships. If you lived in the Star Trek universe, you might have: class Person < ActiveRecord::Base belongs_to :race end class Race < ActiveRecord::Base has_many :people end where @person.race.name should return "human" if you''ve populated the race table and created a foreign key in person named "race_id". -- "Oh, look: rocks!" -- Doctor Who, "Destiny of the Daleks"