mongoengine know when to delete document - django

Question

New to django. I'm doing my best to implement CRUD using Django, mongodb, and mongoengine. I'm able to query the database and render my page with the correct information from the database. I'm also able to change some document fields using javascript and do an Ajax POST back to the original Django View class with the correct csrf token.
The data payload I'm sending back and forth is a list of each Document Model (VirtualPageModel) serialized to json (each element contains ObjectId string along with the other specific fields from the Model.)
This is where it starts getting murky. In order to update the original document in my View Class post function I do an additional query using the object id and loop through the dictionary items, setting the respective fields each time. I then call save and any new data is pushed to the Mongo collection correctly.
I'm not sure if what I'm doing to update existing documents is correct or in the spirit of django's abstracted database operations. The deeper I get the more I feel like I'm not using some fundamental facility earlier on (provided by either django or mongoengine) and because of this I'm having to make things up further downstream.
The way my code is now I would not be able to create a new document (although that's easy enough to fix). However what I'm really curious about is how I would know when to delete a document which existed in the initial query, but was removed by the user/javascript code? Am I overthinking things and the contents of my POST should contain a list of ObjectIds to delete (sounds like a security risk although this would be an internal tool.)
I was assuming that my View Class might maintain either the original document objects (or simply ObjectIds) it queried and I could do my comparisions off of that set, but I can't seem to get that information to persist (as a class variable in VolumeSplitterView) from its inception to when I received the POST at the end.
I would appreciate if anyone could take a look at my code. It really seems like the "ease of use" facilities of Django start to break when paired with Mongo and/or a sufficiently complex Model schema which needs to be directly available to javascript as opposed to simple Forms.
I was going to use this dev work to become django battle-hardened in order to tackle a future app which will be much more complicated and important. I can hack on this thing all day and make it functional, but what I'm really interested in is anyone's experience in using Django + MongoDB + MongoEngine to implement CRUD on a Database Schema which is not vary Form-centric (think more nested metadata).
Thanks.
model.py: uses mongoengine Field types.
class MongoEncoder(JSONEncoder):
def default(self, o):
if isinstance(o, VirtualPageModel):
data_dict = (o.to_mongo()).to_dict()
if isinstance(data_dict.get('_id'), ObjectId):
data_dict.update({'_id': str(data_dict.get('_id'))})
return data_dict
else:
return JSONEncoder.default(self, o)
class SubTypeModel(EmbeddedDocument):
filename = StringField(max_length=200, required=True)
page_num = IntField(required=True)
class VirtualPageModel(Document):
volume = StringField(max_length=200, required=True)
start_physical_page_num = IntField()
physical_pages = ListField(EmbeddedDocumentField(SubTypeModel),
default=list)
error_msg = ListField(StringField(),
default=list)
def save(self, *args, **kwargs):
print('In save: {}'.format(kwargs))
for k, v in kwargs.items():
if k == 'physical_pages':
self.physical_pages = []
for a_page in v:
tmp_pp = SubTypeModel()
for p_k, p_v in a_page.items():
setattr(tmp_pp, p_k, p_v)
self.physical_pages.append(tmp_pp)
else:
setattr(self, k, v)
return super(VirtualPageModel, self).save(*args, **kwargs)
views.py: My attempt at a view
class VolumeSplitterView(View):
#initial = {'key': 'value'}
template_name = 'click_model/index.html'
vol = None
start = 0
end = 20
def get(self, request, *args, **kwargs):
self.vol = self.kwargs.get('vol', None)
records = self.get_records()
records = records[self.start:self.end]
vp_json_list = []
img_filepaths = []
for vp in records:
vp_json = json.dumps(vp, cls=MongoEncoder)
vp_json_list.append(vp_json)
for pp in vp.physical_pages:
filepath = get_file_path(vp, pp.filename)
img_filepaths.append(filepath)
data_dict = {
'img_filepaths': img_filepaths,
'vp_json_list': vp_json_list
}
return render_to_response(self.template_name,
{'data_dict': data_dict},
RequestContext(request))
def get_records(self):
return VirtualPageModel.objects(volume=self.vol)
def post(self, request, *args, **kwargs):
if request.is_ajax:
vp_dict_list = json.loads(request.POST.get('data', []))
for vp_dict in vp_dict_list:
o_id = vp_dict.pop('_id')
original_doc = VirtualPageModel.objects.get(id=o_id)
try:
original_doc.save(**vp_dict)
except Exception:
print(traceback.format_exc())