title: how to create auto increment field in odoo 9
body: <p>In my model, I want to create auto increment field, I 've tried to follow some tuts unfortunately all tutorials just working in odoo 8 to under.
  I just follow instruction from some threat in odoo 9 in this link 
  <a href="https://stackoverflow.com/questions/39266106/auto-increment-internal-reference-odoo9">auto increment - internal reference odoo9</a>
  It was working by answer of <a href="https://stackoverflow.com/users/3734244/danidee">https://stackoverflow.com/users/3734244/danidee</a>
  but still not working for me. Here is my model:</p>
  
  <pre><code>class cashadvance(osv.osv):
      _name = 'comben.cashadvance'
      _columns = {
          'sequence_id': fields.char(string='Sequence ID', help="Auto Generate"),
      }
  
   @api.model
      def create(self, vals):
          vals['sequence_id'] = self.env['ir.sequence'].get('seq.cashadvance')
          return super(cashadvance, self).create(vals)
  </code></pre>
  
  <p>and this is my xml :</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;openerp&gt;
      &lt;data noupdate="1"&gt;
          &lt;record id="cashadvance_seq" model="ir.sequence"&gt;
            &lt;field name="name"&gt;No_PD&lt;/field&gt;
            &lt;field name="padding"&gt;3&lt;/field&gt;
            &lt;field name="code"&gt;seq.cashadvance&lt;/field&gt;
          &lt;/record&gt;
      &lt;/data&gt;
  &lt;/openerp&gt;
  </code></pre>
  
  <p>the code above showing no error but the sequence_id field keep empty when I click save button.
  Help me Please...</p>