Drop unused email column from users table.

app/models/user.rb

@@ -19,6 +19,9 @@ class User < ActiveRecord::Base
   include Roleable
   include HasCustomFields
 
+  # TODO: Remove this after 7th Jan 2018
+  self.ignored_columns = %w{email}
+
   has_many :posts
   has_many :notifications, dependent: :destroy
   has_many :topic_users, dependent: :destroy

db/fixtures/009_users.rb

@@ -33,28 +33,29 @@ UserOption.where(user_id: -1).update_all(
 
 Group.user_trust_level_change!(-1, TrustLevel[4])
 
-# TODO drop email with ignored_columns pattern in rails 5.1
 ColumnDropper.drop(
   table: 'users',
-  after_migration: 'CreateUserEmails',
-  columns:  %w[
-      email_always
-      mailing_list_mode
-      email_digests
-      email_direct
-      email_private_messages
-      external_links_in_new_tab
-      enable_quoting
-      dynamic_favicon
-      disable_jump_reply
-      edit_history_public
-      automatically_unpin_topics
-      digest_after_days
-      auto_track_topics_after_msecs
-      new_topic_duration_minutes
-      last_redirected_to_top_at
-      auth_token
-      auth_token_updated_at ],
+  after_migration: 'DropEmailFromUsers',
+  columns: %w[
+    email
+    email_always
+    mailing_list_mode
+    email_digests
+    email_direct
+    email_private_messages
+    external_links_in_new_tab
+    enable_quoting
+    dynamic_favicon
+    disable_jump_reply
+    edit_history_public
+    automatically_unpin_topics
+    digest_after_days
+    auto_track_topics_after_msecs
+    new_topic_duration_minutes
+    last_redirected_to_top_at
+    auth_token
+    auth_token_updated_at
+  ],
   on_drop: ->() {
     STDERR.puts 'Removing superflous users columns!'
   }

db/migrate/20171107020512_drop_email_from_users.rb

@@ -0,0 +1,9 @@
+class DropEmailFromUsers < ActiveRecord::Migration[5.1]
+  def up
+    # Defer dropping of the columns until the new application code has been deployed.
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end