Django get_object_or_404 with select_related causes form checkbox widget weird behavior : Django 1.4 bug?

Question

I come with a really strange Django 1.4 behaviour wich sounds like a bug to me. I looked anywhere if someone experienced it, but didn't find anything.

My concern is about Django form creation using ModelForm, with a model containing boolean field.

Let Post and Topic two models wich should look like :

class Topic(models.Model):
    my_bool = models.BooleanField(default=False)

class Post(models.Model):
    topic = models.ForeignKey(Topic, related_name='posts')

Now, I'm gonna try to generate a form using TopicForm a class definied elsewhere :

post = Post.objects.get(pk=id_post)
f = TopicForm(instance=post.topic)
print f

It works fine : if in DB my_bool is False, the checkbox is not checked. If my_bool is True, the checkbox is checked. Here is the result :

<p><label for="id_my_bool">my_bool:</label> <input type="checkbox" name="my_bool" id="id_my_bool" /></p>

The problem !

OK, so here is the problem : if I use get_object_or_404 to get my Post object, then my_bool field will always be checked ! Look at this :

post = get_object_or_404(Post.objects.select_related('topic'), pk=id_post)
f = TopicForm(instance=post.topic)
print f

Output (weird) :

<p><label for="id_my_bool">my_bool:</label> <input checked="checked" type="checkbox" name="my_bool" value="0" id="id_my_bool" /></p>

Nota : I tryed several other ways to get the Post object, which all work fine :

• post = Post.objects.filter(pk=id_post)[0]
• post = get_object_or_404(Post, pk=id_post)
• post = Post.objects.get(pk=id_post)

The only thing which makes it bug is :

post = get_object_or_404(Post.objects.select_related('topic'), pk=id_post)

Comments

• With Django 1.3, there wasn't any problem with it : only Django 1.4 makes it bug.
• I found some Django 1.4 bugs which seemed to be related, like :
  • https://code.djangoproject.com/ticket/17747
  • https://code.djangoproject.com/ticket/17114
  • http://groups.google.com/group/django-developers/browse_thread/thread/7d895b2f5fc9ef4b
• I do not use MySQL GIS backend, but django.db.backends.mysql.

Have you got any idea ?

Thank you very much in advance !

Answer 1

Had the same bug in my app and found opened ticket. It seems the main problem is in pair select_related & MySQL: MySQL returns integers for booleans but Django can't associate them with corresponding model when using select_related; consequently, CheckboxInput gets value 0 instead of False and treats it like value in checkbox list.

You can:

1. use patch from ticket;
2. or avoid using select_related;

3. or patch CheckboxInput widget:

   class SingleCheckboxInput(forms.CheckboxInput):
       def render(self, name, value, attrs=None):
           if value in (0, 1):
               value = bool(value)
           return super(SingleCheckboxInput, self).render(name, value, attrs)
   
   class TopicForm(django.forms.ModelForm):
       class Meta:
           model = Topic
           widgets = {'my_bool': SingleCheckboxInput}
   

Answer 2

I see a similar bug, where if I uncheck all boxes, POST data is empty! if I uncehck only one, POST data arrives. Instead of calling get_object_or_404(), examine your inbound request.POST data.