How do I enforce 2 decimal places on API response in Django?

Question

I am making a small API server in Django. For one of my fields, I am using a decimal field which is responsible for representing $ dollar values, so I would like to have 2 decimal places at all times. But I'm struggling to have the exact format.

I'm using rest_framework and my base level response is encoded as a string with the following serializer is:

price = serializers.DecimalField(max_digits=10, decimal_places=2, required=True)

string representation

There is an option to turn off string coercion with "COERCE_DECIMAL_TO_STRING": False in settings.py, but then I face a problem that Decimal is not JSON serializable, and have to use FloatField where I cannot specify a format and end up with only 1 decimal place:

price = serializers.FloatField(required=True)

float representation

I searched for setting up FloatField format on the serializer but did not find any related option. I believe I also tried some other serializers like this one and did not achieve the goal, which is:

How do I enforce 2 decimal places on API response in Django?

Answer 1

Decimal is not supported by json, so formatting float is the only solution. You need to use a custom json encoder that specifies float format for json response and that formatted json is returned from the api.

Your encoder can look something like this:

# Encode Floats as "decimal" with two decimal places
class DecimalEncoder(json.JSONEncoder):
def encode(self, obj):

    if isinstance(obj, dict):
        result = '{'
        for key, value in obj.items():
            if isinstance(value, float):
                encoded_value = format(value, '.2f')
            else:
                encoded_value = json.JSONEncoder.encode(self, value)

            result += f'"{key}": {encoded_value}, '

        result = result[:-2] + '}'
        return result
    return json.JSONEncoder.encode(self, obj)

Reference: https://www.geeksforgeeks.org/json-data-types/