title: how to use date_select(rails)?
body: <p>I have form, and date_select there</p>
  
  <p>here is my form (in edit view)</p>
  
  <pre><code>=form_for @user do |f|
    %p
      = f.date_select('user','birthday',:start_year =&gt; 1940)
  </code></pre>
  
  <p>here is my edit action</p>
  
  <pre><code>def edit
        @user = User.find(params[:id])
   end
  </code></pre>
  
  <p>in my case it writes an error</p>
  
  <blockquote>
    <p>undefined method `merge' for "birthday":String</p>
  </blockquote>
  
  <p>i have attribute birthday:date, also i tryed on string attribute but it didnt work. So how to use date select in my case?(also how to validate it? and how to set default values?)</p>
  
  <p>Thanks in advance</p>