ModelMultipleChoiceField' object has no attribute 'to_field_name' - django

Question

These are my files:
models.py:
class Pierwszy(models.model):
name = models.CharField(max_length=15,blank =True, null= True)
extra = models.CharField(max_length=15,blank =True, null= True)
kids = models.ManyToManyField('Pierwszy', related_name="pierwszy_children", null=True, blank=True)
class Drugi(Pierwszy):
ext_name = models.CharField(max_length=15,blank =True, null= True)
views.py:
class DrugiForm(ModelForm):
def __init__(self, *args, **kwargs):
super(DrugiForm, self).__init__(*args, **kwargs)
instance = getattr(self, 'instance', None)
if instance and instance.pk:
if instance.name is not None:
self.fields['name'].widget.attrs['readonly'] = True
class Meta:
model = Drugi
fields = ('ext_name','name','kids','extra')
widgets = {
'kids' : forms.ModelMultipleChoiceField(queryset=None, widget=forms.CheckboxSelectMultiple()),
}
hidden = {
'extra'
}
template:
<form method="post">{% csrf_token %}
{{ form.non_field_errors }}
{% for hidden in form.hidden_fields %}
{{ hidden }}
{% endfor %}
{% for field in form.visible_fields %}
<div class="fieldWrapper">
{{ field.errors }}
{{ field.label_tag }}: {{ field }}
</div>
{% endfor %}
<p><input type="submit" value="Send message" /></p>
</form>
On this stage I just want to see the current state of object. I don't want to edit fields.
I use queryset=None for kids' widget, because I don't want to show all possibilities, just show list of names (name field) connected to instance.
i'm not sure where should I add filter to queryset (in widget def or in init), but the biggest problem is that, whatever I do, I get
ModelMultipleChoiceField' object has no attribute 'to_field_name'
And I'm stacked now. On Google there's only one case, but this is about overriding the widget/Field - which is not my case.

Answer 1

The widgets dictionary expects the values to be widget instances such as TextArea(), TextInput(), etc.
If you want to use forms.ModelMultipleChoiceField, you could do something like this
class DrugiForm(ModelForm):
kids = forms.ModelMultipleChoiceField(queryset=Pierwszy.objects.none(), widget=forms.CheckboxSelectMultiple())
def __init__(self, *args, **kwargs):
super(DrugiForm, self).__init__(*args, **kwargs)
instance = getattr(self, 'instance', None)
if instance and instance.pk:
if instance.name is not None:
self.fields['name'].widget.attrs['readonly'] = True
class Meta:
model = Drugi
fields = ('ext_name','name','kids','extra')