title: Odoo 8 - Compute Field with "store=True" can't store in database
body: <p>I'm using <code>Odoo 8</code> and I have a problem with <code>compute field</code> with type is <code>Many2One</code>.</p>
  
  <p>Here, I declared <code>department_id</code>:</p>
  
  <pre><code>department_id = fields.Text(
      string="Department", store=True,
      comodel_name="hr.department",
      compute="_get_department_id"
  )
  </code></pre>
  
  <p>And fuction of this compute field:</p>
  
  <pre><code>@api.depends('employee_id')
  def _get_department_id(self):
      if self.employee_id.department_id:
          self.department_id = self.employee_id.department_id.name
  </code></pre>
  
  <p>It seems to work right now, but it's not. In view, I can see the value of <code>department_id</code>. But in the database, the table has no column <code>department_id</code> and has no value of this column.</p>
  
  <p><strong>My question is: how can I store the <code>department_id</code> in database?</strong></p>
  
  <p>Notes:</p>
  
  <ul>
  <li>In the declaration of <code>department_id</code>, I set <code>store=True</code>, but it did NOT store the value of this field in database.</li>
  <li><p>I did a test. I add <code>compute_field</code> with type <code>Text</code>, It works, I don't know why compute field doesn't work with type <code>Many2One</code>.</p>
  
  <pre><code>@api.depends('employee_id')
  def _get_compute_field(self):
  if self.employee_id.department_id:
      self.compute_field = self.employee_id.department_id.name
  
  compute_field = fields.Text(
      string="Compute Field", store=True,
      compute="_get_compute_field"
  )
  </code></pre></li>
  </ul>