json serialize python and mongoengine object mix

Question

json.dumps(o) converts a native python object to json
o.to_json() converts a mongoengine object such as Document to json

How do you convert a mixed object?
e.g a python dict, with mongoengine objects as its values?

Are there tools for this? Or should I create a custom JSONEncoder class?

If I do override the encoder, could I create a decoder that reconstructs also the mongoengine objects?

Jonathan Livni · Accepted Answer · 2014-10-07 12:15:19Z

1

The following encoder serializes python\mongoengine object mixes

import json
from mongoengine.base import BaseDocument

class MongoengineObjectsJsonEncoder(json.JSONEncoder):
    def default(self, o):
        if isinstance(o, BaseDocument):
            return o._data
        elif isinstance(o, datetime):
            return o.isoformat()
        else:
            return json.JSONEncoder.default(self, o)

Notes:

This encoder does not add any signature regarding where the python objects end and mongoengine objects begin, so it can't be automatically deserialized correctly to python\mongoengine objects, but rather it will deserialize to a single python object
I've also added datetime object serialization to ISO 8601 format

answered Oct 7, 2014 at 12:15

Jonathan Livni

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5 Comments

Ross Over a year ago

That won't work, the default json encoder cant handle mongo's data types correctly as bson is a supertype of json. MongoEngine just uses pymongo (see bson.json_utils) for the encoding of individual objects or querysets so you should use that for documents eg: return json_utils.dumps(o.to_mongo())

Jonathan Livni Over a year ago

@Ross - do you mean instead of the specific line return o._data?

Jonathan Livni Over a year ago

@Ross - Assuming yes on the above comment, AFAIK if default() returns a str instead of a dict then later in the decoding the entire object will remain as a string, so maybe you mean return o.to_mongo()

Jonathan Livni Over a year ago

@Ross ping on my questions above :)

Dmitry Yudin Over a year ago

i solved my problem by from bson.json_util import dumps and in the end return dumps(o)

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