Question

Trying to use Django MongoDBForms to replace ModelForms but I get this really weird error when saving the instance of the form.

During save(), mongoengine.Document checks for the cascade keyword in the _meta dict which MongoDBForm wraps.

MongoDBForm then throws a KeyError from getitem

What’s that cascade key it’s looking for?!

Am I doing it wrong?

Request Method: POST
Request URL:    http://localhost:8000/add_item/Books
Django Version: 1.4.2
Exception Type: KeyError
Exception Value:    
0
Exception Location: /Users/holografix/.virtualenvs/troca/lib/python2.7/site-packages/mongodbforms/documentoptions.py in __getitem__, line 171
Python Executable:  /Users/holografix/.virtualenvs/troca/bin/python
Python Version: 2.7.3

The model from models.py

class GenericItem(Document):
    owner_id = IntField(required=True)
    title = StringField(max_length=70, required=True)
    description = StringField(max_length=140, required=True)
    value = IntField()
    location = GeoPointField()
    offers = ListField(EmbeddedDocumentField('Offer'))

    def __unicode__(self):
        return self.title

    class Meta:
        abstract = False
        app_label = 'troca_app'
        db_table = 'generic_item'
        allow_inheritance = True

ModelForm equivalent in forms.py

class ModelFormGenericItem(DocumentForm):
   class Meta:
       document = GenericItem
       fields = ('title', 'value', 'description')

View where I process the form

@login_required
def add_item(request, category):

    if request.method == 'POST':        

        if category == 'Muffins':
            form = ModelFormMuffin(request.POST)        

        elif category == 'Cameras':
            form = ModelFormCameras(request.POST)        

        else:        
            form = ModelFormGenericItem(request.POST)

        form = ModelFormGenericItem(request.POST)

        if form.is_valid():
            #process the data in form.cleaned_data

            instance = form.save(commit = False)
            instance.owner_id = request.user.id
            instance.save(safe=True, cascade=)

            return HttpResponseRedirect('/thanks/')

    else:
        # Ensure that this is a "final" category:
        p = get_object_or_404( Category, categoryTitle = category )        
        i = Category.objects.filter( parentCategory = p )
        if i.count() != 0:
            raise Http404

        if category == 'Muffins':
            form = ModelFormMuffin()

        elif category == 'Cameras':
            form = ModelFormCameras()

        else:        
            form = ModelFormGenericItem()

    return render(request, 'item.html', {
        'form': form,
        'category': category,
    } )

More from the Django error:

/Users/holografix/Documents/development/troca_proj/troca_app/views.py in add_item
            instance.save() ...
▶ Local vars
/Users/holografix/.virtualenvs/troca/lib/python2.7/site-packages/mongoengine/document.py in save
            warn_cascade = not cascade and 'cascade' not in self._meta ...
▶ Local vars
/Users/holografix/.virtualenvs/troca/lib/python2.7/site-packages/mongodbforms/documentoptions.py in __getitem__
        return self.meta[key] ...
▶ Local vars

Answer 1

EDIT:
Implementing a contains() method for documentoptions.py seems to fix it without needing to change anything else.

Ended up hacking around this issue as I have no idea why it’s happening…

Added a “has_key()” method to mongodbforms.documentoptions as such:

def has_key(self, key):
    return self.meta.has_key(key)

and changing the offending line from mongoengine from the in operator to a check on the has_key() method:

warn_cascade = not cascade and not self._meta.has_key('cascade')

If anyone could answer just WTF the original error is popping up, that’d be awesome!