Provide mapping model to json and back with custom fields

services.py

import abc

from django.forms.models import model_to_dict


class Mapping(abc.ABC):
    model = None
    fields = {}

    @classmethod
    def json_to_model(cls, json):
        return cls.model(
            **{
                field: json.get(mapped)
                for field, mapped in cls.fields.items()
                if json.get(mapped)
            }
        )

    @classmethod
    def model_to_json(cls, instance):
        return {
            cls.fields[field]: value
            for field, value in model_to_dict(
                instance, fields=list(cls.fields)
            ).items()
        }

    @classmethod
    def update_model(cls, instance, json):
        for field, mapped in cls.fields.items():
            value = json.get(mapped)
            if value:
                setattr(instance, field, value)
        instance.save()


class PositionMapping(Mapping):
    model = Position
    fields = {
        'ext_position_id': 'ext_position_id',
        'delivery_order': 'delivery_order_id',
        'consignment': 'consignment_id'
    }