title: Error: Element '<field name="x y z">' cannot be located in parent view
body: <p>I have created a computed field in python code, bom.py (please see below) and added that field in the view bom_view.xml. The field name is "old_default_code" and associated function in python code is _old_default_code(). However, when I try to update (refresh) the module I am getting an error: </p>
  
  <pre><code>"Error details: "Field `old_default_code" does not exist"
  </code></pre>
  
  <p>What am I doing wrong?</p>
  
  <p>Here is the code snippet from bom.py:</p>
  
  <pre><code>class mrp_bom(osv.osv):
      _inherit = 'mrp.bom'
  
          def _old_default_code(self, cr, uid, ids, name, arg, context=None):
              return True
  
      _columns = {'x_roll_material': fields.float('Standard Material Cost', digits=(16, 4), readonly=True),
          'x_bom_time_average': fields.float('Average BOM Lead Time', digits=(16, 4), readonly=True),
          'x_bom_time_last': fields.float('Last BOM Lead Time', digits=(16, 4), readonly=True),
          'old_default_code' : fields.function(_old_default_code, type='char', size=32, method=True, store=False, multi=False) }
  </code></pre>
  
  <p>and here is the XML code:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;openerp&gt;
      &lt;data&gt;
          &lt;!-- mrp_bom --&gt;
          &lt;record id="adamson_mrp_bom_form_view" model="ir.ui.view"&gt;
              &lt;field name="name"&gt;adamson.mrp.bom.form.view&lt;/field&gt;
              &lt;field name="model"&gt;mrp.bom&lt;/field&gt;
              &lt;field name="type"&gt;form&lt;/field&gt;
              &lt;field name="inherit_id" ref="mrp.mrp_bom_form_view" /&gt;
              &lt;field name="arch" type="xml"&gt;
                  &lt;field name="old_default_code" /&gt;
                  &lt;xpath expr="//notebook/page[@string='Components']/field/tree[@string='Components']/field[@name='sequence']" position="before" &gt;
  
                       &lt;button class="oe_inline oe_stat_button" type="object" string="Go!" icon="gtk-go-forward" name="action_go" 
                       attrs="{'invisible':[('old_default_code','=', False)]}"  /&gt;
                                 &lt;/xpath&gt;
  </code></pre>