Add Callout model

app/models/callout.rb

+class Callout < ActiveRecord::Base
+  belongs_to :user
+end

app/models/user.rb

@@ -139,6 +139,7 @@ class User < ActiveRecord::Base
   has_many :assigned_merge_requests,  dependent: :nullify, foreign_key: :assignee_id, class_name: "MergeRequest" # rubocop:disable Cop/ActiveRecordDependent
 
   has_many :custom_attributes, class_name: 'UserCustomAttribute'
+  has_many :callouts
 
   #
   # Validations

db/migrate/20180125214301_create_callouts.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class CreateCallouts < ActiveRecord::Migration
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  def change
+    create_table :callouts do |t|
+      t.string :feature_name, null: false
+      t.boolean :dismissed_state, null: false
+      t.references :user, index: true, foreign_key: { on_delete: :cascade }, null: false
+
+      t.timestamps_with_timezone null: false
+    end
+
+    add_index :callouts, :feature_name, unique: true
+  end
+end