title: how to make a unique column in rails active records other than id
body: <pre><code>class CreateUsers &lt; ActiveRecord::Migration
     def up
       create_table :users do |t|
          t.string "email", :unique=&gt;true
  </code></pre>
  
  <p>I was trying to add this unique option for making this email id unique in rails model but its not working so how can i make this email id unique ?</p>