title: Is there a better way to deal with unique field in yii2 curd form?
body: <p>In my yii2 form I have a field name <code>number</code>, which is unique in DB.</p>
  
  <p>This <code>number</code> will be used for sorting in frontend.</p>
  
  <p>Whats the best way to deal with this field in backend?</p>