Hey everyone... I'm just getting my feet wet with relational databases using RoR models. The software I'm putting together relies on car parts. Originally I had the database set up as follows create_table :parts do |t| t.column :year, :string t.column :make, :string t.column :model, :string . . . end However, I now realize it's much better to do it using relationships instead. Unfortunately, I'm not too familiar with this method and have been reading up on it for a few hours. I just want to post what I think I'm supposed to be doing here and hopefully get a little feedback as to whether I'm approaching this correctly before I start programming it into my application... class Year < ActiveRecord::Base has_many :makes end class Make < ActiveRecord::Base belongs_to :year has_many :models, :through => something_else end class Model < ActiveRecord::Base belongs_to :make has_many :parts, :through => something end class Part < ActiveRecord::Base belongs_to :model end However, I guess what is confusing me is that if I try to set it up this way, if I enter a part for a 1999 Jeep Cherokee, how would I link the part (say with part_id = 1337) to 1999, Jeep, and Cherokee? Would I need to refine my setup here and link the part directly to the year, make, and model by adding belongs_to and has_many or would I simply add a column for make_id, model_id, year_id to my "create_table :parts" method? ie: create_table :parts do |t| t.column :year_id t.column :make_id t.model :model_id end The other thing confusing me is the ":through => something" stuff. In one example I see can see creating a friendship table that links two users, but I'm not sure how I would apply it in this case or if it is even smart to do it this way... Any help would be appreciated. Thanks!
on 2009-04-24 09:44
on 2009-04-24 10:58
On 24 Apr 2009, at 06:38, email@example.com wrote: > > However, I guess what is confusing me is that if I try to set it up > this way, if I enter a part for a 1999 Jeep Cherokee, how would I link > the part (say with part_id = 1337) to 1999, Jeep, and Cherokee? Would > I need to refine my setup here and link the part directly to the year, > make, and model by adding belongs_to and has_many or would I simply > add a column for make_id, model_id, year_id to my > "create_table :parts" method? ie: > well you'd take your part_id, look at that row in the parts table, see that it has model_id 123456. Then look at that model and then you could see from the make_id and so on that it was a jeep etc.. > through is for when you have a many to many relation ship, so for example if one part can be used by several different models, it might be appropriate to have a has many through between parts and models. on the other hand, a given model belongs to precisely 1 make, so belongs_to/has_many should be fine. You may find http://guides.rubyonrails.org/association_basics.html helpful Another thing is that it's hard to talk about the 'best way' when talking in generalities. The shape of the data you have and the sort of questions you want to be able to ask about that data or things you need to do with it are important: play around with some setups and and arrangements. If a particular scheme makes a common task difficult/ slow, odds are it's not right for you! Fred