Rails - build_association is not working for a has_one and belongs_to relationship
activerecord, associations, ruby-on-rails
Solution
According to your model associations, a `Subscription` is a child of a `Client`.
If you create a subscription first and then create a client as per your first example, Rails has no way of setting a `client_id` foreign key value within the `subscriptions` table because at that point you haven't created the client record, so there's nothing to associate with the subscription. That's why you have to create the parent record (i.e. a client) first and then associate it with a child subscription record using the `build_subscription` method.
Problem
I have two models ``` class Subscription < ActiveRecord::Base belongs_to :client end class Client < ActiveRecord::Base has_one :subscription end ``` but when I try to create a parent from the child e.g. sub.build_client the foreign key does not get set e.g. ``` >> sub = Subscription.new => #<Subscription id: nil, token: nil, user_id: nil, created_at: nil, updated_at: nil, cancelled: nil, active: nil, client_id: nil> >> sub.save(false); ?> client = sub.build_client => #<Client id: nil, server_id: nil, ip: nil, created_at: nil, updated_at: nil> >> client.save(false) => true >> sub.client_id => nil >> sub => #<Subscription id: 4, token: nil, user_id: nil, created_at: "2010-01-11 06:07:45", updated_at: "2010-01-11 06:07:45", cancelled: nil, active: nil, client_id: nil> ``` It does work if I do client.build_subscription ``` ?> client = Client.new => #<Client id: nil, server_id: nil, ip: nil, created_at: nil, updated_at: nil> >> client.save(false) => true >> sub = client.build_subscription => #<Subscription id: nil, token: nil, user_id: nil, created_at: nil, updated_at: nil, cancelled: nil, active: nil, client_id: 4> >> sub.save(false) => true >> sub => #<Subscription id: 5, token: nil, user_id: nil, created_at: "2010-01-11 06:09:32", updated_at: "2010-01-11 06:09:32", cancelled: nil, active: nil, client_id: 4> >> client => #<Client id: 4, server_id: nil, ip: nil, created_at: "2010-01-11 06:09:02", updated_at: "2010-01-11 06:09:02"> >> ^C ``` Ive spent 3 hours fiddling and got nowhere fast. Can anyone explain what I'm doing wrong, things to check etc