How do I validate a unique `social_media_account.type` per `user` in Rails?

Question

I have many users, and they has_many :social_media_accounts, however, I want to only allow a unique social_media_account.type per user,

e.g. User "Bob" can only have one social_media_account.type of "Twitter"

How do I do this?

class User < ApplicationRecord
  has_many :social_media_accounts
end

class SocialMediaAccount < ApplicationRecord
  belongs_to :user

  enum type: [
    twitter:   1,
    facebook: 2,
    linkedin: 3
  ]
end

add custom validation to user and check it here. or add unique constraint — Andrey Saleba, Aug 23 '16 at 07:20
DB way: you can add unique constraint for `user_id` and `social_media_account_id` so you will be assured there's only one record of `social_media_account` for one `user`.App way: you can add custom validates method, which will check existence of social_media_account on creation/modification of user as you need\ — Andrey Saleba, Aug 23 '16 at 07:35
@AndreyS we can validate a combined uniqueness of two attributes? I didn't know that! Please post that in the answer with a reference and i'll accept it! — Amin Shah Gilani, Aug 23 '16 at 07:36
@AndreyS: were you talking about scope: http://guides.rubyonrails.org/active_record_validations.html#uniqueness — Amin Shah Gilani, Aug 23 '16 at 07:38

score 1 · Accepted Answer · edited May 23 '17 at 12:01

You can solve it two ways:

On DB side: create migration for unique index for your user_id and social_media_account_id. Example is here: A migration to add unique constraint to a combination of columns
On the app side: create validation preventing of creating more than one social_media_account for one user (Example: validates :name, uniqueness: { scope: :year}). More info here: http://guides.rubyonrails.org/active_record_validations.html

How do I validate a unique `social_media_account.type` per `user` in Rails?

1 Answers1