want to return percentage in Django Rest Framework

Question

• I wanted to return the percentage of every poll options_data in response.
• I'm Expecting output Like in below.

{
    "response": true,
    "return_code": "remove_vote_success",
    "result": {
        "id": 9,
        "user_id": 2,
        "question": "what would you like to see more of on our channel?",
        "created_on": "2022-09-06T05:52:39",
        "active": true,
        "options_data": [
            {
                "id": 25,
                "poll_id": 9,
                "option_text": "Video editing tutorials",
                "percentage_count": 50.0
            },
            {
                "id": 26,
                "poll_id": 9,
                "option_text": "Clipchamp product updates",
                "percentage_count": 10.0
            },
            {
                "id": 27,
                "poll_id": 9,
                "option_text": "Social media growth tips"
                "percentage_count": 40.0
            },
            {
                "id": 28,
                "poll_id": 9,
                "option_text": "Clipchamp tips and tricks",
                "percentage_count": 0.0
            }
        ]
    },
    "message": "Vote get successfully."
}

• this is my models.py

class Polls(models.Model):
    user = models.ForeignKey(User, related_name="polls_data", on_delete=models.CASCADE)
    question = models.TextField(max_length=250, blank=False, null=False)
    created_on = models.DateTimeField(default=timezone.now)
    active = models.BooleanField(default=True)


class Options(models.Model):
    poll = models.ForeignKey(Polls, related_name="options_data", on_delete=models.CASCADE)
    option_text = models.CharField(max_length=255)


class Vote(models.Model):
    user = models.ForeignKey(User, related_name="vote_data", on_delete=models.CASCADE)
    poll = models.ForeignKey(Polls, on_delete=models.CASCADE)
    option = models.ForeignKey(Options, on_delete=models.CASCADE)

• this is my serializer.py

class OptionsSerializer(serializers.ModelSerializer):

    class Meta:
        model = Options
        fields = ('id', 'poll_id', 'option_text')

class PollsSerializer(serializers.ModelSerializer):
    
    options_data = OptionsSerializer(many=True, read_only=True)

    class Meta:
        model = Polls
        fields = ('id','user_id', 'question', 'created_on', 'active',  'options_data')

Answer 1

if we return values direct in response there maybe you will face ZeroDivisionError. so for code efficiency use this.

class OptionsSerializer(serializers.ModelSerializer):

    percentage_count = serializers.SerializerMethodField()

    class Meta:
        model = Options
        fields = ('id', 'poll_id', 'option_text', 'percentage_count')

    def get_percentage_count(self, obj): 
       total_votes = Vote.objects.filter(poll_id=obj.poll).count()
       share_of_votes = Vote.objects.filter(option_id=obj).count()
       try:
            percentage = Decimal((share_of_votes / total_votes) * 100).quantize(Decimal('.01'))
       except ZeroDivisionError:
            return 0 
       return percentage

class PollsSerializer(serializers.ModelSerializer):
    
    options_data = OptionsSerializer(many=True, read_only=True)

    class Meta:
        model = Polls
        fields = ('id','user_id', 'question', 'created_on', 'active',  'options_data')

Answer 2

In your OptionsSerializeradd a field that takes the .count() of the option in question and divide by the count() of all answers for that question. (then multiply that by 100 to get to percentage)

class OptionsSerializer(serializers.ModelSerializer):
    percentage_count = serializers.SerializerMethodField()

    ...

    def get_percentage_count(self, obj): 
       total_votes = Vote.objects.filter(poll=obj.poll).count()
       share_of_votes = Vote.objects.filter(option=obj).count()
       return Decimal(
           (share_of_answers / total) * 100
       ).quantize(Decimal('.01'))