Django REST Framework: object is None only on one attribute, but not other

Question

I have been having trouble understanding why the object (obj) passed into field_to_native() changes from Nonetype to a correct object once I change the attribute...

Here's the original issue: Splitting model instance for serializer into 3 different fields

mariodev from stackoverflow helped me on the original issue, but a strange bug both of us cannot figure out:

Here's the code where it seems to have the problem:

COORD = dict(x=0, y=1, z=2)
class CoordField(serializers.Field):
    def field_to_native(self, obj, field_name):
        #retrieve and split coords
        coor = obj.xyz.split('x')
        return int(coor[COORD[field_name]])

class NoteSerializer(serializers.ModelSerializer):
    owner = serializers.Field(source='owner.username')
    firstname = serializers.Field(source='owner.first_name')
    lastname = serializers.Field(source='owner.last_name')
    x = CoordField()
    y = CoordField()
    z = CoordField()


class Meta:
    model = Note
    fields = ('id','owner','firstname','lastname','text','color','time','x', 'y', 'z')

xyz is a instance in the model Note. According to the traceback, when I do obj.xyz, the obj = None.

Weirdly, if I do obj.color, the obj returns correctly (Note: someuser)

I don't understand how the obj can change just by changing the attribute.

What's beyond me is that the JSON data 'x' 'y' and 'z' ARE being passed to the view, and my div boxes get the correct left, top, and z-index CSS data. If this works, why am I getting an error?

If there's an error, why is the data still getting through?

style="left: 343px; top: 110px; z-index: 3;"

As you can see, the x,y,z DID pass through.

Any enlightenment would be wonderful! Thanks a bunch!

Here's the traceback in text view:

Traceback:
File "/home1/thecupno/python2.7/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response
  140.                     response = response.render()
File "/home1/thecupno/python2.7/lib/python2.7/site-packages/django/template/response.py" in render
  105.             self.content = self.rendered_content
File "/home1/thecupno/python2.7/lib/python2.7/site-packages/rest_framework/response.py" in rendered_content
  59.         ret = renderer.render(self.data, media_type, context)
File "/home1/thecupno/python2.7/lib/python2.7/site-packages/rest_framework/renderers.py" in render
  582.         post_form = self.get_rendered_html_form(view, 'POST', request)
File "/home1/thecupno/python2.7/lib/python2.7/site-packages/rest_framework/renderers.py" in get_rendered_html_form
  485.             data = serializer.data
File "/home1/thecupno/python2.7/lib/python2.7/site-packages/rest_framework/serializers.py" in data
  510.                 self._data = self.to_native(obj)
File "/home1/thecupno/python2.7/lib/python2.7/site-packages/rest_framework/serializers.py" in to_native
  309.             value = field.field_to_native(obj, field_name)
File "/home1/thecupno/django/notes/desk/serializers.py" in field_to_native
  10.         coor = obj.xyz#.split('x')      <-- I commented out .split, and the problem still persists.
Exception Type: AttributeError at /desk/restnote/
Exception Value: 'NoneType' object has no attribute 'xyz'

Could you provide a complete failing case? At the moment it's a little hard to understand what's going on - for example, where is that traceback coming from, if you get a successful response? — Hamish
– Hamish, Commented Sep 29, 2013 at 20:54
Okay, so I am able to get JSON data of 'x', 'y', 'z' from my getJSON on my HTML page. What's weird is, when I visit the REST Web API url, it says "Nonetype has no attribute xyz" when it clearly just processed xyz into separete 'x' 'y' 'z' JSON. It seems if it's being processed 2 times, one with the object, and one without. If I use another attribute (like color), the object returns correctly. Because I have an server error, I cannot do anything else. What's weird is that even with a server error, it still gives me GET data... — Kevin Tomiyoshi Yang
– Kevin Tomiyoshi Yang, Commented Sep 29, 2013 at 22:36
Basically, if I do obj.xyz, with the DEBUG tool in Django, it says obj = None. When I do obj.color, it returns correctly as <Note: someusername>. Yet, in my getJSON() on my HTML page, I still got the JSON data for obj.xyz. What? — Kevin Tomiyoshi Yang
– Kevin Tomiyoshi Yang, Commented Sep 29, 2013 at 22:40

Kevin Tomiyoshi Yang · Accepted Answer · 2013-09-30 06:56:45Z

3

I have solved my own problem. The solution was to make sure the the serializer returns None if the object is none.

Here's the corretion to the top code portion:

COORD = dict(x=0, y=1, z=2)
class CoordField(serializers.Field):
def field_to_native(self, obj, field_name):
    if obj is None:
        return None
    else:
        #retrieve and split coords
        coor = obj.xyz.split('x')
        return int(coor[COORD[field_name]])

Hope this helps fellow Django programmers!

answered Sep 30, 2013 at 6:56

Kevin Tomiyoshi Yang

1061 silver badge10 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Django REST Framework: object is None only on one attribute, but not other

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related