Rails - Jul 2007 - has_one vs. has_many - Something just isn't seeming right... (Can someone explain?)

Hey everyone, I''m really just starting Rails and I posted a day or  
two ago with my first question.  I think I''m needing to back up here  
because something just isn''t seeming right.  I am hoping someone  
might be kind enough to shed some light on ActiveRecord & the right  
way to set things up.

In my little test application I have models for Account, User,  
ServicePlan.  The idea is that a person joins by first choosing a  
service plan, and then chooses an Account Name and a User login  
name.  After the account is created multiple users can be added to  
the account.  The options for the account are determined by the  
service plan, so someone on Plan 1 might get 20 downloads a month,  
while Plan 5 might get unlimited downloads.

Now as far as object relations go, an Account "has_many" users, which
works fine.  The problem however comes in when I start under the  
assumption that an Account "has_one" service plan.  Rails
doesn''t
error, & my validations pass, but nothing is saved to the DB table  
(I''m still learning the unit test stuff so my tests aren''t
even
written, let alone pass so they give me no help yet).

The problem is there should be (as per good DB design) only one  
record per service plan, so I''m starting to think that Account  
"has_one" ServicePlan is not correct.  An Account does not own a  
service plan, it just retains a reference to the service plan a user  
chose, which can be changed at any time the user wishes.

I thought perhaps ServicePlans "has_many" Accounts, but that
doesn''t
seem right either.  In working with an account, I should be able to  
access it''s options by saying MyAccount.service_plan.someOption  
(shouldn''t I?) because the service plan that was chosen is a property  
of the Account.  Also, HABTM doesn''t seem quite right because
it''s
not a many-to-many relationship, it''s many-to-one.

Anyway, I''m just running in circles here and getting more confused.   
Can anyone point me in the right direction?  I''d be really grateful.

- Cliff


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I think you want something like this

class User < ActiveRecord::Base
  belongs_to :account
end

# an account can have many users
class Account < ActiveRecord::Base
  belongs_to :service_plan
  has_many :users
end

# each account belongs to a service plan, so all users in the account
# will have the same service plan
class ServicePlan < ActiveRecord::Base
  has_many :accounts
end

Mike

On 7/9/07, Cliff Pruitt
<lists.cpruitt-0X7n6C/JC56123jP4xv/FQ@public.gmane.org>
wrote:
>
> Hey everyone, I''m really just starting Rails and I posted a day or
> two ago with my first question.  I think I''m needing to back up
here
> because something just isn''t seeming right.  I am hoping someone
> might be kind enough to shed some light on ActiveRecord & the right
> way to set things up.
>
> In my little test application I have models for Account, User,
> ServicePlan.  The idea is that a person joins by first choosing a
> service plan, and then chooses an Account Name and a User login
> name.  After the account is created multiple users can be added to
> the account.  The options for the account are determined by the
> service plan, so someone on Plan 1 might get 20 downloads a month,
> while Plan 5 might get unlimited downloads.
>
> Now as far as object relations go, an Account "has_many" users,
which
> works fine.  The problem however comes in when I start under the
> assumption that an Account "has_one" service plan.  Rails
doesn''t
> error, & my validations pass, but nothing is saved to the DB table
> (I''m still learning the unit test stuff so my tests
aren''t even
> written, let alone pass so they give me no help yet).
>
> The problem is there should be (as per good DB design) only one
> record per service plan, so I''m starting to think that Account
> "has_one" ServicePlan is not correct.  An Account does not own a
> service plan, it just retains a reference to the service plan a user
> chose, which can be changed at any time the user wishes.
>
> I thought perhaps ServicePlans "has_many" Accounts, but that
doesn''t
> seem right either.  In working with an account, I should be able to
> access it''s options by saying MyAccount.service_plan.someOption
> (shouldn''t I?) because the service plan that was chosen is a
property
> of the Account.  Also, HABTM doesn''t seem quite right because
it''s
> not a many-to-many relationship, it''s many-to-one.
>
> Anyway, I''m just running in circles here and getting more
confused.
> Can anyone point me in the right direction?  I''d be really
grateful.
>
> - Cliff
>
>
> >
>
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On Jul 9, 2007, at 11:18 AM, Mike Garey wrote:
> # an account can have many users
> class Account < ActiveRecord::Base
>   belongs_to :service_plan
>   has_many :users
> end
>
> # each account belongs to a service plan, so all users in the account
> # will have the same service plan
> class ServicePlan < ActiveRecord::Base
>   has_many :accounts
> end
Thanks Mike, That''s what I started to think, but it didn''t
seem quite
correct from a data modeling standpoint.  Maybe it''s just adapting to  
the way rails does things & I just need to adjust.  It doesn''t seem
like a service plan should really "own" anything at all, but I  
understand now how it technically works within Rails.  I had tried  
exactly what you''d recommended before but another (very stupid in  
hindsight) mistake in my controller kept it from having any effect or  
generating any error, so your email was enough to push me back into  
looking a little harder.  It''s now working. Thanks a lot.

- Cliff


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