odoo 9 AssertionError assert self in records and field in fs
finally I found the problem:
the problem is that the method of the computed field is not exist (I renamed it accidentally). so when odoo try to get the value of this field it failed, and show this strange error
while I am trying to update value that affect computed field I got this error:

Odoo Server Error
  Traceback (most recent call last):
    File "/Users/abdalla/projects/greenway/odoo-server/openerp/http.py", line 647, in _handle_exception
      return super(JsonRequest, self)._handle_exception(exception)
    File "/Users/abdalla/projects/greenway/odoo-server/openerp/http.py", line 684, in dispatch
      result = self._call_function(**self.params)
    File "/Users/abdalla/projects/greenway/odoo-server/openerp/http.py", line 320, in _call_function
      return checked_call(self.db, *args, **kwargs)
    File "/Users/abdalla/projects/greenway/odoo-server/openerp/service/model.py", line 118, in wrapper
      return f(dbname, *args, **kwargs)
    File "/Users/abdalla/projects/greenway/odoo-server/openerp/http.py", line 313, in checked_call
      result = self.endpoint(*a, **kw)
    File "/Users/abdalla/projects/greenway/odoo-server/openerp/http.py", line 963, in call
      return self.method(*args, **kw)
    File "/Users/abdalla/projects/greenway/odoo-server/openerp/http.py", line 513, in response_wrap
      response = f(*args, **kw)
    File "/Users/abdalla/projects/greenway/odoo-server/addons/web/controllers/main.py", line 904, in call_kw
      return self._call_kw(model, method, args, kwargs)
    File "/Users/abdalla/projects/greenway/odoo-server/addons/web/controllers/main.py", line 896, in _call_kw
      return getattr(request.registry.get(model), method)(request.cr, request.uid, *args, **kwargs)
    File "/Users/abdalla/projects/greenway/odoo-server/openerp/api.py", line 250, in wrapper
      return old_api(self, *args, **kwargs)
    File "/Users/abdalla/projects/greenway/odoo-server/openerp/api.py", line 381, in old_api
      result = method(recs, *args, **kwargs)
    File "/Users/abdalla/projects/greenway/odoo-server/openerp/models.py", line 6036, in onchange
      record.mapped(field_seq)
    File "/Users/abdalla/projects/greenway/odoo-server/openerp/models.py", line 5534, in mapped
      recs = recs._mapped_func(operator.itemgetter(name))
    File "/Users/abdalla/projects/greenway/odoo-server/openerp/models.py", line 5514, in _mapped_func
      vals = [func(rec) for rec in self]
    File "/Users/abdalla/projects/greenway/odoo-server/openerp/models.py", line 5752, in getitem
      return self._fields[key].get(self, type(self))
    File "/Users/abdalla/projects/greenway/odoo-server/openerp/fields.py", line 829, in get
      self.determine_value(record)
    File "/Users/abdalla/projects/greenway/odoo-server/openerp/fields.py", line 927, in determine_value
      record._prefetch_field(self)
    File "/Users/abdalla/projects/greenway/odoo-server/openerp/api.py", line 248, in wrapper
      return new_api(self, *args, **kwargs)
    File "/Users/abdalla/projects/greenway/odoo-server/openerp/models.py", line 3295, in _prefetch_field
      assert self in records and field in fs
  AssertionError