title: how to access attr_accessor in rails model using `attribute_names` method
body: <p>I need to access attribute names of a model but it is not showing all of them.</p>
  
  <p>I have User model and I added a <code>attr_accessor :color</code> in it (since I don't want to store this on my database as column).
  But if I try to access attribute names using <code>User.first.attribute_names</code> it is showing only database columns,it is not showing 'color' attribute,so how do I access all the attributes ?is there any methods which list attr_accessor as attributes ?</p>