django-rest-framework: How Do I Serialize a Field That Already Contains JSON?

Question

I am pretty new to the django-rest-framework, so could use some help.

I have an object with a TextField that is a string containing JSON.

I\'m using django-r

Answer 1

You can simply decode the json into python object:

json_obj = json.loads(model.json_text)

Once you serialize your object, replace this field with the decoded object:

data = serializer.data
data["field"] = json_obj
return Response(data)

Answer 2

I solved this another way:

1: use a JSON-Field for the JSON content (django-jsonfield or django-json-field should be fine). These then will to loads/dumps as needed

2: in my serializer, use the transform-method to prevent the data added as string to the response

class MyModelSerializer(serializers.ModelSerializer):
    def transform_myjsonfield(self, obj, value):
        return obj.myjsonfield

    class Meta:
        model = MyModel

If you need write-access, you only have to add a method validate_myjsonfield which converts back.

(of course, this could be also done with a custom DRF serializer field.

Answer 3

Here is what works for me on, djangorestframework==3.9.1:

import json

from rest_framework import serializers

from .models import WeatherLocation


class WeatherLocationSerializer(serializers.ModelSerializer):
    LocationId = serializers.CharField(source='location_id')
    City = serializers.CharField(source='city')
    Region = serializers.CharField(source='region')
    Name = serializers.CharField(source='name')
    Country = serializers.CharField(source='country')
    WeatherForecastLongTermTimePeriods = serializers.JSONField(required=False, allow_null=True,
                                                               source='weather_forecast_long_term_time_periods')
    WeatherForecastShortTermTimePeriods = serializers.JSONField(required=False, allow_null=True,
                                                                source='weather_forecast_short_term_time_periods')

    def to_representation(self, instance):
        ret = super(WeatherLocationSerializer, self).to_representation(instance)
        ret['WeatherForecastLongTermTimePeriods'] = json.loads(ret['WeatherForecastLongTermTimePeriods'])
        ret['WeatherForecastShortTermTimePeriods'] = json.loads(ret['WeatherForecastShortTermTimePeriods'])
        return ret

    class Meta:
        model = WeatherLocation
        fields = ['LocationId', 'City', 'Region', 'Name', 'Country',
                  'WeatherForecastLongTermTimePeriods', 'WeatherForecastShortTermTimePeriods', ]

I thought there would be an easier way to do this, but by changing the behaviour of to_representation, I can convert my text fields to JSON. For reference, here is my models.py:

from django.db import models


class WeatherLocation(models.Model):
    """
    Weather app schema, from southparc
    """
    location_id = models.CharField(primary_key=True, null=False, blank=False, default=None, max_length=254,
                                   editable=True)
    region = models.CharField(max_length=2, null=False, blank=False)
    city = models.CharField(null=False, blank=False, max_length=254)
    province = models.CharField(null=True, blank=True, max_length=254)
    name = models.CharField(null=True, blank=True, max_length=254)
    country = models.CharField(null=True, blank=True, max_length=254)

    # JSON fields
    weather_forecast_long_term_time_periods = models.TextField(default="", blank=True)
    weather_forecast_short_term_time_periods = models.TextField(default="", blank=True)

    # Dates
    created_date = models.DateTimeField(auto_now_add=True)
    modified_date = models.DateTimeField(auto_now=True)

Hope that helps. If you use a JSONField that is supported by Postgres, I'm sure you won't need to do this. I'm using a TextField to save my JSON here. I thought that specifying the field type as serializers.JSONField on the serializer would be enough but its not the case.