Rails: create on belongs_to association

Question

Hi (huge Rails newbie here), I have the following models:

class Shop < ActiveRecord::Base
belongs_to :user
validates_uniqueness_of :title, :user_id, :message => "is already being used"
end

and

class User < ActiveRecord::Base
has_one :shop, :dependent => :destroy
end

When I'm about to create a new shop, I get the following error:

private method `create' called for nil:NilClass

This is my controller:

@user = current_user
@shop = @user.shop.create(params[:shop])

I've tried different variations by reading guides and tutorials here and there, but I'm more confused than before and can't get it to work. Any help would be greatly appreciated.

Answer 1

First of all, here is how to do what you want:

@user = current_user
@shop = Shop.create(params[:shop])
@user.shop = @shop

Now here's why your version did not work:

You probably thought that this might work because if User had a has_many relation to Shop, @user.shops.create(params[:shop]) would work. However there is a big difference between has_many relations and has_one relations.

With a has_many relation, shops returns an ActiveRecord collection object, which has methods that you can use to add and remove shops to/from a user. One of those methods is create, which creates a new shop and adds it to the user.

With a has_one relation, you don't get back such a collection object, but simply the Shop object the belongs to the user - or nil if the user doesn't have a shop yet. Since neither Shop objects nor nil have a create method, you can't use create this way with has_one relations.