CODEWITHSUNDEEP
ruby-on-railsruby
tehAnswer
tehAnswer

Reputation: 1018

Ensure belongs_to combination is unique

I don't know what is the proper manner to ensure that there is only one record with the same couple of foreign keys. Let's assume a class named LineItem, which belongs to an cart and to item. Something like:

class LineItem < ActiveRecord::Base
  belongs_to :cart
  belongs_to :item

The point is: I want to make unique the combination of this two "attributes". At this time, my approach was using a after_save callback but I realized thats pretty poor. How do you resolve this? I was thinking in a PORO class (something like LineItemSaver) but I'm not completely convinced.

Thanks!

Upvotes: 1

Views: 4290

Answers (3)

Pavan
Pavan

Reputation: 33542

If I understood your question correctly,you want the scope option of the validates_uniqueness_of. If so, this should work.

In your LineItem model:

class LineItem < ActiveRecord::Base

  belongs_to :cart
  belongs_to :item 
  validates_uniqueness_of :cart_id, scope: :item_id

end

And also, you should be generating a migration to add this:

add_index :line_items, [ :cart_id, :item_id ], :unique => true

More Info here.

Upvotes: 5

Jimmy Baker
Jimmy Baker

Reputation: 3255

Try using a validate method to ensure that item_id is unique scoped to :cart_id

Something like:

validates :item_id, uniqueness: { scope: :cart_id }

Or if you want to fix the situation and simply increment the quantity you could also:

validate :ensure_line_item_uniqueness

def ensure_line_item_uniqueness
  ... whatever fixes the situation here ...
end

Upvotes: 2

nzifnab
nzifnab

Reputation: 16110

Can't you just do a uniqueness validation?

validates :cart_id, uniqueness: {scope: :item_id}

Upvotes: 2

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