title: How to update compute fields which have store=True in Odoo8?
body: <p>I have modified an existing field, <code>date_due</code>. I made it depend on <code>multi_date_due</code> (a one2many field I have created)', but it does not change when <code>multi_date_due</code> is modified. However, if I set store to False in <code>date_due</code>, the field is updated rightly.</p>
  
  <p>I have tried to reinstall my module, to replace the original field in both python and xml code, but no way.</p>
  
  <p>Python code:</p>
  
  <pre><code>class account_invoice(models.Model):
  
      _inherit = 'account.invoice'
      _logger = logging.getLogger(__name__)
  
      date_due = fields.Date(
          string='Due date',
          readonly=False,
          compute=lambda self: self._compute_date_due(),
          store=True,
      )
  
      @api.multi
      @api.depends('multi_date_due.date_due')
      def _compute_date_due(self):
          for record in self:
              last_date = \
                  datetime.strptime("9999-12-31 23:59:59", "%Y-%m-%d %H:%M:%S")
              if record.multi_date_due:
                  for multi_date_due in record.multi_date_due:
                      self._logger.warning(multi_date_due.date_due)
                      if datetime.strptime(\
                          multi_date_due.date_due, "%Y-%m-%d") &lt; last_date:
                          first_date = multi_date_due.date_due
              else:   
                  first_date = None
              record.date_due = first_date
  </code></pre>
  
  <p>XML code:</p>
  
  <pre><code>&lt;record id="invoice_supplier_form" model="ir.ui.view"&gt;
      &lt;field name="name"&gt;account.invoice.supplier.form&lt;/field&gt;
      &lt;field name="model"&gt;account.invoice&lt;/field&gt;
      &lt;field name="inherit_id" ref="account.invoice_supplier_form"/&gt;
      &lt;field name="arch" type="xml"&gt;
          &lt;data&gt;
              &lt;xpath expr="//field[@name='date_due']" position="replace"&gt;
                  &lt;field name="date_due"/&gt;
              &lt;/xpath&gt;
              &lt;xpath expr="//field[@name='date_due']" position="after"&gt;
                  &lt;field name="multi_date_due" widget="one_to_many_list"&gt;
                      &lt;tree string="Multiple due dates"&gt;
                          &lt;field name="date_due" string="Due date"/&gt;
                          &lt;field name="invoice" invisible="1"/&gt;
                      &lt;/tree&gt;
                  &lt;/field&gt;
              &lt;/xpath&gt;
          &lt;/data&gt;
      &lt;/field&gt;
  &lt;/record&gt;
  </code></pre>
  
  <p>This solution does not works for me:
  <a href="https://stackoverflow.com/questions/28834086/odoo-8-compute-field-with-store-true-cant-store-in-database">Odoo 8 - Compute Field with &quot;store=True&quot; can&#39;t store in database</a></p>
  
  <p>Thanks!</p>