Rails doesn't respect model associations for has_one

Question

User.rb

has_one :subscription, :inverse_of => :user

Subscription.rb

has_one :credit_card, :inverse_of => :subscription

CreditCard.rb

belongs_to :user, :inverse_of => :credit_card
belongs_to :subscription, :inverse_of => :credit_card

In credit card controller:

def new
   @credit_card = current_user.build_credit_card
end

def create
   @credit_card = current_user.build_credit_card
end

if @credit_card.save
    if @credit_card.save
    format.html { redirect_to @credit_card, notice: 'Credit card was successfully created.' }
    format.json { render action: 'show', status: :created, location: @credit_card }
  else
    format.html { render action: 'new' }
    format.json { render json: @credit_card.errors, status: :unprocessable_entity }
  end
end

However, I'm still able to add multiple credit cards to my user model. How can this be possible? Only a has_many should emit such behaviour if I'm correct? A has_one association should prevent additional entities from being created, apart from one as far as I know..

I tried all variations, but still no luck.

Any help would be much appreciated!

Thank you.

What do you mean that it works? What code runs to add multiple cards, and what makes you think it's working when it shouldn't? — dpassage, Nov 28 '13 at 20:53
A user has_one credit card, but still any given user is able to create multiple cards? In short, it behaves as if it's a has_many when it's a has_one association. I hope this clarifies my question.. — dsignr, Nov 28 '13 at 21:02

score 2 · Accepted Answer · edited May 23 '17 at 12:22

2

I've never used a has_one relationship but the power of google and stack overflow has helped me understand this.

Difference between has_one and belongs_to in Rails?

belongs_to means that the foreign key is in the table for this class. So belongs_to can ONLY go in the class that holds the foreign key.

has_one

means that there is a foreign key in another table that references this class. So has_one can ONLY go in a class that is referenced by a column in another table.

Also a nice way to remember it in that post:

I always think of it in terms of Toy Story. Andy 'has_one' Woody, Woody 'belongs_to' andy. Where is the foreign key? On Woody's sole.

Also this is useful for understanding relationships.

http://requiremind.com/differences-between-has-one-and-belongs-to-in-ruby-on-rails/

edited May 23 '17 at 12:22

Community

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answered Nov 28 '13 at 21:25

Shaun Frost Duke Jackson

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For you and me both :) – Shaun Frost Duke Jackson Nov 29 '13 at 14:30
Informative BUT...how do you prevent your application from actually creating more than one record (in the op's example, prevent adding multiple credit cards for a user)? Would it be to add to the following to the user model? validates :card_id, uniqueness: {scope: :user_id} – rmcsharry May 13 '16 at 16:11

Rails doesn't respect model associations for has_one

1 Answers1