Optimize sign in: Identity #2061 (#2231)

* Add unique index to identity

* Conditional uniqueness validations on identities

* Remove redundant Identity specs

app/models/identity.rb

@@ -1,9 +1,8 @@
 class Identity < ApplicationRecord
   belongs_to :user
   validates :uid, :provider, presence: true
-  validates :uid, uniqueness: { scope: :provider }
-  validates :provider, uniqueness: { scope: :uid }
-  validates :user_id, uniqueness: { scope: :provider }
+  validates :uid, uniqueness: { scope: :provider }, if: proc { |i| i.uid_changed? || i.provider_changed? }
+  validates :user_id, uniqueness: { scope: :provider }, if: proc { |i| i.user_id_changed? || i.provider_changed? }
   validates :provider, inclusion: { in: %w[github twitter] }
 
   serialize :auth_data_dump

db/migrate/20190327090030_add_indexes_to_indentities.rb

@@ -0,0 +1,6 @@
+class AddIndexesToIndentities < ActiveRecord::Migration[5.1]
+  def change
+    add_index :identities, %i[provider uid], unique: true
+    add_index :identities, %i[provider user_id], unique: true
+  end
+end

db/schema.rb

@@ -1,5 +1,3 @@
-# frozen_string_literal: true
-
 # This file is auto-generated from the current state of the database. Instead
 # of editing this file, please use the migrations feature of Active Record to
 # incrementally modify your database, and then regenerate this schema definition.
@@ -12,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20190318223433) do
+ActiveRecord::Schema.define(version: 20190327090030) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
 
@@ -412,6 +410,8 @@ ActiveRecord::Schema.define(version: 20190318223433) do
     t.string "uid"
     t.datetime "updated_at", null: false
     t.integer "user_id"
+    t.index ["provider", "uid"], name: "index_identities_on_provider_and_uid", unique: true
+    t.index ["provider", "user_id"], name: "index_identities_on_provider_and_user_id", unique: true
   end
 
   create_table "job_opportunities", force: :cascade do |t|

spec/models/identity_spec.rb

@@ -5,7 +5,6 @@ RSpec.describe Identity, type: :model do
   it { is_expected.to validate_presence_of(:uid) }
   it { is_expected.to validate_presence_of(:provider) }
   it { is_expected.to validate_uniqueness_of(:uid).scoped_to(:provider) }
-  it { is_expected.to validate_uniqueness_of(:provider).scoped_to(:uid) }
   it { is_expected.to validate_uniqueness_of(:user_id).scoped_to(:provider) }
   it { is_expected.to validate_inclusion_of(:provider).in_array(%w[github twitter]) }
   it { is_expected.to serialize(:auth_data_dump) }