Rails - Apr 2006 - Validations and has_many :through (Join Models)

Hello again:

I''m hoping that somebody, anybody, can help with this question.

How do I make sure that records in a join model are unique?

Using the scenario outlined in Chad Fowler''s "Rails
Recipies", number
16, "Many to Many Relationships Where the Relationship Iteself Has 
Data".

Here are the tables:

create_table :magazines do |t|
  t.column :title, :string
end

create_table :readers do |t|
  t.column :name, :string
end

create_table :subscriptions do |t|
  t.column :reader_id, :integer
  t.column :magazine_id, :integer
  t.column :last_renewal_on, :date
  t.column :length_in_issues, :integer
end

And here are the models:

class Subscription < ActiveRecord::Base
  belongs_to :reader
  belongs_to :magazine
end

class Reader < ActiveRecord::Base
  has_many :subscriptions
  has_many :magazines, :through => :subscriptions
end

class Magazine < ActiveRecord::Base
  has_many :subscriptions
  has_many :readers, :through => :subscriptions
end

Here''s the code I''m using to test:

magazine = Magazine.create(:title => "Ruby Illustrated")
reader = Reader.create(:name => "Anthony Braxton")
subscription = Subscription.create(:last_renewal_on => Date.today,
                 :length_in_issues => 6)
reader.subscriptions << subscription
magazine.subscriptions << subscription
subscription.save
subscription2 = Subscription.create(:last_renewal_on => (Date.today+1),
                  :length_in_issues => 12)
reader.subscriptions << subscription2
magazine.subscriptions << subscription2
subscription2.save

After all of that, there now exists 2 records in the subscriptions 
table, both of which have the same reader_id and magazine_id.  How do 
you perform the validation to make sure that each record in the 
subscriptions table has a unique reader_id, magazine_id pair?

Thanks.

-- 
Posted via http://www.ruby-forum.com/.

Hello David,

[...]
> After all of that, there now exists 2 records in the subscriptions
> table, both of which have the same reader_id and magazine_id.
>  How do you perform the validation to make sure that each record
> in the subscriptions table has a unique reader_id, magazine_id
> pair?
Try this :

class Subscription < ActiveRecord::Base
  belongs_to :reader
  belongs_to :magazine

  validates_uniqueness_of :reader_id, :scope => :magazine_id
end

Good night,

    -- Jean-Fran?ois.

--
? la renverse.

Jean-Fran?ois wrote:
> Hello David,
> 
> [...]
>> After all of that, there now exists 2 records in the subscriptions
>> table, both of which have the same reader_id and magazine_id.
>>  How do you perform the validation to make sure that each record
>> in the subscriptions table has a unique reader_id, magazine_id
>> pair?
> 
> Try this :
> 
> class Subscription < ActiveRecord::Base
>   belongs_to :reader
>   belongs_to :magazine
> 
>   validates_uniqueness_of :reader_id, :scope => :magazine_id
> end
> 
> Good night,
> 
>     -- Jean-Fran?ois.
Thanks Jean-Fran?ois!

Originally I tried putting a validates_uniqueness_of in the Subscription 
model, but I used validates_uniqueness_of :reader, :scope => :magazine. 
Of course it didn''t work.  And I didn''t think of using the
id''s
directly, because I was not thinking and didn''t want to put database 
details in if I didn''t have to.  Duh, the model is where those sort of 
things are supposed to go!

As I said, thanks again.

-- 
Posted via http://www.ruby-forum.com/.

With ref to this post, will using a naming convention of 
magazines_subscriptions yield any reduction in effort?  Or is the 
through used because the subscription table is named outside of the 
convention?

IM having a very hard time accessing and displaying joined data...i 
thought i might have got my head round it after the first 40 
hours...grrrr...

I will post more on my specific problem if i dont come across an answer 
in the archive...

David Willis wrote:
> Jean-Fran?ois wrote:
>> Hello David,
>> 
>> [...]
>>> After all of that, there now exists 2 records in the subscriptions
>>> table, both of which have the same reader_id and magazine_id.
>>>  How do you perform the validation to make sure that each record
>>> in the subscriptions table has a unique reader_id, magazine_id
>>> pair?
>> 
>> Try this :
>> 
>> class Subscription < ActiveRecord::Base
>>   belongs_to :reader
>>   belongs_to :magazine
>> 
>>   validates_uniqueness_of :reader_id, :scope => :magazine_id
>> end
>> 
>> Good night,
>> 
>>     -- Jean-Fran?ois.
> 
> Thanks Jean-Fran?ois!
> 
> Originally I tried putting a validates_uniqueness_of in the Subscription 
> model, but I used validates_uniqueness_of :reader, :scope => :magazine. 
> Of course it didn''t work.  And I didn''t think of using
the id''s
> directly, because I was not thinking and didn''t want to put
database
> details in if I didn''t have to.  Duh, the model is where those
sort of
> things are supposed to go!
> 
> As I said, thanks again.

-- 
Posted via http://www.ruby-forum.com/.