add index in migrate file

db/migrate/20170403155230_create_employees.rb

@@ -3,15 +3,16 @@ class CreateEmployees < ActiveRecord::Migration[5.1]
     create_table :employees do |t|
       t.string :name, :null => false
       t.string :role, :null => false, :default => "cashier"
-      t.boolean :is_active, :default => true
+      t.boolean :is_active, :default => true, :index=>true
       t.string :emp_id, :null => false
       t.string :password_digest, :null => false
-      t.string :token_session
+      t.string :token_session, :index=>true
       t.datetime :session_expiry
       t.datetime :session_last_login
       t.string :created_by
       t.string :image_path
       t.timestamps
     end
+    add_index :employees, [:is_active, :token_session]
   end
 end