Add association between referral and referrer

[PatrickMcSweeny]

Closes #736

Pull request checklist

• My code contains tests covering the code I modified
• I linted and tested the project with bin/check
• I added significant changes and product updates to the changelog

[joemasilotti]

I don't want any referral-based columns to exist on the users table, so I think we still need another model. The diagram in the issue outlined a ReferralCode which belongs_to :user and I think we still want that.

This will rework the associations on the User model to has_one :referral_code, has_one :referrer, and has_many :referrals with the necessary through: options.

We can also add a unique constraint to the code on the new table in the database, along with the existing Rails validation.

[PatrickMcSweeny]

Currently there is a has_one :referral association on the User model so I think it would be confusing to have a has_many :referrals association.

[joemasilotti]

Good point. I think that it should actually be has_one :referral and has_many :referees.

[PatrickMcSweeny]

@joemasilotti I updated the commit

[joemasilotti]

Thanks for the updates! I pulled down the code and I think I glossed over a major fallacy with this approach: it is terribly hard to reason around what is going on! Not your code, but the data modeling that I proposed.

Thanks to your initial commit I'm leaning back towards getting rid of the ReferralCode model entirely. Instead, a Referral can have an optional relationship with the referrer. I think that should simplify things quite a bit.

I also think that I haven't given the naming conventions of this enough though. Here's what I'd love the naming to be:

• A user has one referrer - the person who referred them
• A user has many referrals - the people they've referred
• A referral belongs to a referee (of class "User")
• A referral belongs to an optional referrer (of class "User")

Which I think means we need to add where clauses to the relationship references on the user model. Otherwise, it would always include records where the user was a referrer or referee.

---

Does that make sense? Or am I overthinking this?

Let me know if you'd like to give it another pass. And no worries if not – I understand I've jumped around a lot with this one!

[PatrickMcSweeny]

That comes pretty close to the commit I originally made. The main difference is that the relationship I used for the referrals made the user is referrals_made.

[PatrickMcSweeny]

I pushed the original commit to the remote branch. Take a look and let me know if it needs any adjustments.

[joemasilotti]

Awesome, thank you again!

I pulled out the referral-related code to a module and tweaked the names a bit more. I think that in theory "referrer" and "referee" make sense but in practice I have a hard time wrapping my head around which is which.

I like where this Referrable model ended up, especially the alias.

module Referrable
  extend ActiveSupport::Concern

  included do
    has_one :referral, foreign_key: "referred_user_id", dependent: :destroy
    has_one :referring_user, through: :referral
    alias_method :referred_by, :referring_user

    has_many :referrals, foreign_key: "referring_user_id", dependent: :nullify
    has_many :referred_users, through: :referrals

    validates :referral_code, uniqueness: true, allow_nil: true
  end
end

user.referred_by # => User
user.referred_users # => [User]