Getting started with database/model relationships

Rails
1

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!

2

Hey Bernhard,

take a look first into this. There is a really good explanation, hope
you come along with this.

Rafael

On 24 Apr., 07:47, Bradley H. [email protected]

3

I think I’m making some progress here, but what I’m wondering about now
is whether or not my full-text search using acts_as_ferret will still
work. Right now, in the old database setup I have, the text search will
find everything in the parts table. However, lets say I link part1 with
model1 through a model_id (or part_id), will searching parts for
“model1” yield a result?

4

Okay… Here is what I have… Let me know if I should make any
refinements…

class Year < ActiveRecord::Base
has_many :makes
has_many :models, :through => :make
has_many :parts, :through => :model
end

class Make < ActiveRecord::Base
belongs_to :year
has_many :models
has_many :parts, :through => :model
end

class Model < ActiveRecord::Base
belongs_to :make
belongs_to :year
has_many :parts
end

class Part < ActiveRecord::Base
belongs_to :model
belongs_to :make
belongs_to :year
end

5

Ideally I’d like a part to have a year_id, make_id, and model_id. I’d
like a model to have a single make_id but have the option of belonging
to several years (aka: Corvette could have years 1952 thru 2009). The
make would belong to several years and have several makes (ie. Chevy
from 1911-Present, and models like Corvette, Malibu, Camaro, etc…). I
don’t know why this is confusing me so much, but any help would be
appreciated.