check duplicate record

db/migrate/20180810041316_create_setting.rb

@@ -0,0 +1,9 @@
+class CreateSetting < ActiveRecord::Migration[5.0]
+  def change
+    create_table :settings do |t|
+      t.string :key
+      t.string :value
+      t.string :name
+    end
+  end
+end