How to serialize cleaned_data if it contains models? - django

Question

I'm trying to serialize some form data so that I can stuff it into a hidden field until the user is ready to submit the whole form (think of a wizard).
I'm trying this:
print simplejson.dumps(vehicle_form.cleaned_data)
But I keep getting errors like this:
<VehicleMake: Honda> is not JSON serializable
Really I just need it to output the PK for "Honda".
This doesn't work either:
print serializers.serialize('json', vehicle_form.cleaned_data)
Gives:
'str' object has no attribute '_meta'
Presumably because it's iterating over the keys, which are all strings, whereas I think it expects a queryset, which I don't have.
So how do I do this?
Okay, so far I've come up with this:
from django.utils.simplejson import JSONEncoder, dumps, loads
from django.utils.functional import curry
from django.db.models import Model
from django.db.models.query import QuerySet
from django.core.serializers import serialize
class DjangoJSONEncoder(JSONEncoder):
def default(self, obj):
if isinstance(obj, Model):
return obj.pk
elif isinstance(obj, QuerySet):
return loads(serialize('json', obj, ensure_ascii=False))
return JSONEncoder.default(self, obj)
json_encode = curry(dumps, cls=DjangoJSONEncoder)
json_decode = loads
Based on the answers I found [here][1]. Now I'm trying this:
json = json_encode(vehicle_form.cleaned_data)
data = json_decode(json)
vehicle = Vehicle(**data)
The first 2 lines work perfectly, but the 3rd results in an exception:
Cannot assign "3": "Vehicle.model" must be a "VehicleModel" instance.
Getting close! Not sure how to deal with this one though...

Answer 1

This is a bit of a hack, but I don't know of a better way:
try:
vehicle_data = simplejson.loads(request.POST['vehicle_data'])
except ValueError:
vehicle_data = []
vehicle_data.append(vehicle_form.raw_data())
request.POST['vehicle_data'] = simplejson.dumps(vehicle_data)
It grabs the JSON data from hidden field in your form and decodes it into a Python dict. If it doesn't exist, it starts a new list. Then it appends the new raw/uncleaned data and re-encodes it and dumps it into the hidden field.
For this to work you need to either make a copy of the POST data (request.POST.copy()) so that it becomes mutable, or hack it like I did: request.POST._mutable = True
In my form template I put this:
<input type="hidden" name="vehicle_data" value="{{request.POST.vehicle_data}}" />
And lastly, to access the raw data for a form I added these methods:
from django.forms import *
def _raw_data(self):
return dict((k,self.data[self.add_prefix(k)]) for k in self.fields.iterkeys())
def _raw_value(self, key, value=None):
if value is None:
return self.data[self.add_prefix(key)]
self.data[self.add_prefix(key)] = value
Form.raw_data = _raw_data
Form.raw_value = _raw_value
ModelForm.raw_data = _raw_data
ModelForm.raw_value = _raw_value
Since .data returns too much data (in fact, it just returns the POST data you initially passed in), plus it's got the prefixes, which I didn't want.