style(rubocop): resolve Rails/UniqueValidationWithoutIndex with DB indexes

.rubocop_todo.yml

@@ -184,13 +184,4 @@ Rails/SkipsModelValidations:
     - 'app/controllers/workshop_invitation_controller.rb'
     - 'app/services/invitation_logger.rb'
 
-# Offense count: 8
-Rails/UniqueValidationWithoutIndex:
-  Exclude:
-    - 'app/models/auth_service.rb'
-    - 'app/models/chapter.rb'
-    - 'app/models/feedback_request.rb'
-    - 'app/models/invitation.rb'
-    - 'app/models/meeting_invitation.rb'
-    - 'app/models/workshop_invitation.rb'
-    - 'app/models/workshop_sponsor.rb'
+

app/models/auth_service.rb

@@ -1,4 +1,4 @@
 class AuthService < ApplicationRecord
   belongs_to :member, optional: true
-  validates :uid, uniqueness: { constraint: :provider }
+  validates :uid, uniqueness: { scope: :provider }
 end

db/migrate/20260731104506_add_unique_indexes_for_unique_validations.rb

@@ -0,0 +1,13 @@
+class AddUniqueIndexesForUniqueValidations < ActiveRecord::Migration[8.1]
+  def change
+    add_index :auth_services, %i[uid provider], unique: true
+    add_index :chapters, :name, unique: true
+    add_index :chapters, :email, unique: true
+    add_index :feedback_requests, %i[member_id workshop_id], unique: true
+    add_index :feedback_requests, :token, unique: true
+    add_index :invitations, %i[member_id event_id role], unique: true
+    add_index :meeting_invitations, %i[member_id meeting_id], unique: true
+    add_index :workshop_invitations, %i[member_id workshop_id role], unique: true
+    add_index :workshop_sponsors, %i[sponsor_id workshop_id], unique: true
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.1].define(version: 2026_07_29_151201) do
+ActiveRecord::Schema[8.1].define(version: 2026_07_31_104506) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_catalog.plpgsql"
 
@@ -75,6 +75,7 @@
     t.string "uid"
     t.datetime "updated_at", precision: nil
     t.index ["member_id"], name: "index_auth_services_on_member_id"
+    t.index ["uid", "provider"], name: "index_auth_services_on_uid_and_provider", unique: true
   end
 
   create_table "bans", id: :serial, force: :cascade do |t|
@@ -102,6 +103,8 @@
     t.string "slug"
     t.string "time_zone", default: "London", null: false
     t.datetime "updated_at", precision: nil
+    t.index ["email"], name: "index_chapters_on_email", unique: true
+    t.index ["name"], name: "index_chapters_on_name", unique: true
   end
 
   create_table "chapters_events", id: :serial, force: :cascade do |t|
@@ -242,7 +245,9 @@
     t.string "token"
     t.datetime "updated_at", precision: nil
     t.integer "workshop_id"
+    t.index ["member_id", "workshop_id"], name: "index_feedback_requests_on_member_id_and_workshop_id", unique: true
     t.index ["member_id"], name: "index_feedback_requests_on_member_id"
+    t.index ["token"], name: "index_feedback_requests_on_token", unique: true
     t.index ["workshop_id"], name: "index_feedback_requests_on_workshop_id"
   end
 
@@ -349,6 +354,7 @@
     t.index ["event_id", "attending"], name: "index_invitations_event_attending"
     t.index ["event_id"], name: "index_invitations_on_event_id"
     t.index ["member_id", "attending"], name: "index_invitations_member_attending"
+    t.index ["member_id", "event_id", "role"], name: "index_invitations_on_member_id_and_event_id_and_role", unique: true
     t.index ["member_id"], name: "index_invitations_on_member_id"
     t.index ["verified_by_id"], name: "index_invitations_on_verified_by_id"
   end
@@ -391,6 +397,7 @@
     t.index ["meeting_id", "attending"], name: "index_meeting_invitations_meeting_attending"
     t.index ["meeting_id"], name: "index_meeting_invitations_on_meeting_id"
     t.index ["member_id", "attending"], name: "index_meeting_invitations_member_attending"
+    t.index ["member_id", "meeting_id"], name: "index_meeting_invitations_on_member_id_and_meeting_id", unique: true
     t.index ["member_id"], name: "index_meeting_invitations_on_member_id"
   end
 
@@ -601,6 +608,7 @@
     t.datetime "updated_at", precision: nil
     t.integer "workshop_id"
     t.index ["member_id", "attending"], name: "index_workshop_invitations_member_attending"
+    t.index ["member_id", "workshop_id", "role"], name: "idx_on_member_id_workshop_id_role_e3cea6bbfd", unique: true
     t.index ["member_id"], name: "index_workshop_invitations_on_member_id"
     t.index ["token"], name: "index_workshop_invitations_on_token", unique: true
     t.index ["workshop_id", "attending"], name: "index_workshop_invitations_workshop_attending"
@@ -613,6 +621,7 @@
     t.integer "sponsor_id"
     t.datetime "updated_at", precision: nil
     t.integer "workshop_id"
+    t.index ["sponsor_id", "workshop_id"], name: "index_workshop_sponsors_on_sponsor_id_and_workshop_id", unique: true
     t.index ["sponsor_id"], name: "index_workshop_sponsors_on_sponsor_id"
     t.index ["workshop_id", "host"], name: "index_workshop_sponsors_on_workshop_id_and_host"
     t.index ["workshop_id"], name: "index_workshop_sponsors_on_workshop_id"