Add associations between users via invitations

app/models/invitation.rb

@@ -1,6 +1,7 @@
 class Invitation < ApplicationRecord
   # Relations
   belongs_to :user
+  belongs_to :invitee, class_name: "User", foreign_key: 'invited_user_id', optional: true
 
   # Validations
   validates_presence_of :user

app/models/user.rb

@@ -3,6 +3,10 @@ class User < ApplicationRecord
 
   # Relations
   has_many :invitations, dependent: :destroy
+  has_one  :invitation, inverse_of: :invitee, foreign_key: 'invited_user_id'
+  has_one  :inviter, through: :invitation, source: :user
+  has_many :invitees, through: :invitations
+
   has_many :donations, dependent: :nullify
 
   has_one  :lndhub_user, class_name: "LndhubUser", inverse_of: "user",