Cannot deserialize properly a response using pymongo

Question

I was using an API that were written in NodeJS, but for some reasons I had to re-write the code in python. The thing is that the database is in MongoDB, and that the response to all the queries (with large results) includes a de-serialized version with$id as, for example {$oid: "f54h5b4jrhnf}.

this object id representation with the nested $iod instead of just the plain string that Node use to return, is messing with the front end, and I haven't been able to find a way to get just the string, rather than this nested object (other than iterate in every single document and extract the id string) without also changing the way the front end treat the response

is there a solution to get a json response of the shape [{"_id":"63693f438cdbc3adb5286508", etc...} ?

I tried using pymongo and mongoengine, both seems unable to de-serialize in a simple way

Answer 1

You have several options (more than mentioned below).

MongoDB

In a MongoDB query, you could project/convert all ObjectIds to a string using "$toString".

Python

Iterate, like you mention in your question.

--OR--

You could also define/use a custom pymongo TypeRegistry class with a custom TypeDecoder and use it with a collection's CodecOptions so that every ObjectId read from a collection is automatically decoded as a string.

Here's how I did it with a toy database/collection.

from bson.objectid import ObjectId
from bson.codec_options import TypeDecoder

class myObjectIdDecoder(TypeDecoder):
    bson_type = ObjectId
    def transform_bson(self, value):
        return str(value)

from bson.codec_options import TypeRegistry
type_registry = TypeRegistry([myObjectIdDecoder()])

from bson.codec_options import CodecOptions
codec_options = CodecOptions(type_registry=type_registry)

collection = db.get_collection('geojson', codec_options=codec_options)

# the geojson collection _id field values have type ObjectId
# but because of the custom CodecOptions/TypeRegistry/TypeDecoder
# all ObjectId's are decoded as strings for python
collection.find_one()["_id"]
# returns '62ae621406926107b33b523c' I.e., just a string.