Mongoengine Document object can't update using from_json

Question

From here,

I need to update my existing document data using from_json.

When I am using from_json like

>> user = User.objects(pk=2).first()
>> print user.to_json()

above shows

>> {"_id": 1, "_cls": "User", "name": "OldName"}

now I update existing user object

>> user = user.from_json(json.dumps({"_id": 1, "_cls": "User", "name": "NewName"}))
>> user.save()
>> print user.to_json()

it shows

>> {"_id": 1, "_cls": "User", "name": "NewName"}

But it cannot update in DB.

Again I querying same user it shows

>> {"_id": 1, "_cls": "User", "name": "OldName"}

My Question is how can I update existing data using document object method from_json?

Answer 1

For me the following worked:

user.update(**mydictname) #mydictname contains the dictionary of values I want to update
user.save()
user.reload() #not doing this makes the changes available only after the object is reloaded elsewhere

Answer 2

That I'm afraid is a common issue and probably not been resolved yet, this is a link to the source code of MongoEngine and you can search "from_json" to see if you can hack around by figuring out what this function is actually doing: https://github.com/MongoEngine/mongoengine/blob/master/mongoengine/queryset/base.py;

For me, I simply iterate over the (key, value) of the json data and set that manually by:

Batman = User.objects.get('user_id'='blah')
data = {'username':'batman', 'password':'iLoveGotham'}
for (key, val) in data.items():
  Batman[key] = val
Batman.save()

It works, but hopefully the from_json function could actually work so that this process would become more elegant.

Answer 3

Does it not update if you search in a Mongo Shell for the document either? If not, stop reading here. Saving does not automatically update the object, but I think if you call something like:

>> user = user.from_json(json.dumps({"_id": 1, "_cls": "User", "name": "NewName"}))
>> user.save()
>> user.reload()
>> print user.to_json()

Just learning Mongoengine myself, but here is a good resource: http://docs.mongoengine.org/guide/