How do I access a method from my Model in Django in React - json

Question

In the following model...
class Question(models.Model):
question_text = models.CharField(max_length=200)
likes = models.IntegerField(default=0)
dislikes = models.IntegerField(default=0)
pub_at = models.DateTimeField(auto_now_add=True)
category = models.ForeignKey(
Category, on_delete=models.SET_NULL, null=True)
def __str__(self):
return f"{self.question_text}"
def validity(self):
total_likes = self.likes + self.dislikes
if total_likes != 0:
return (self.likes / total_likes) * 100
else:
return 100
I want to be able to access Question.objects.get(pk=1).validity() assuming that pk=1 exists in this case. In python shell I can do this easily. But how do I do this using React. I am able to get all my questions and the fields in React without a problem but I don't think I have a way to access the validity method I created.

Answer 1

In this case I would suggest the following. First, remove the property from the model:
# models.py
class Question(models.Model):
question_text = models.CharField(max_length=200)
likes = models.IntegerField(default=0)
dislikes = models.IntegerField(default=0)
pub_at = models.DateTimeField(auto_now_add=True)
category = models.ForeignKey(
Category, on_delete=models.SET_NULL, null=True)
def __str__(self):
return f"{self.question_text}"
Then add a SerializerMethodField (docs) to your serializer. It is read-only and can be used to pass computed values to your views:
# serializers.py
class QuestionSerializer(serializers.ModelSerializer):
validity = serializers.SerializerMethodField()
class Meta:
model = Question
fields = ['question_text', 'likes', 'dislikes', 'pub_at', 'category', 'validity']
def get_validity(self, instance):
total_likes = instance.likes + instance.dislikes
# Your approach is not wrong. This is a more explicit way of dealing with that particular error type
try:
return (instance.likes / total_likes) * 100
except ZeroDivisionError:
return 100
Bear in mind that the Foreign Key category will be serialized as its database unique id value (Primary Key) in this case.

Answer 2

You might want to use the #property decorator so that you can access the value the same way you would access any of the other fields on your Question model:
class Question(models.Model):
question_text = models.CharField(max_length=200)
likes = models.IntegerField(default=0)
dislikes = models.IntegerField(default=0)
pub_at = models.DateTimeField(auto_now_add=True)
category = models.ForeignKey(
Category, on_delete=models.SET_NULL, null=True)
def __str__(self):
return f"{self.question_text}"
#property
def validity(self):
total_likes = self.likes + self.dislikes
percentage = (self.likes / total_likes) * 100
return percentage
Explanations can be found in the docs or here. Keep in mind that it will not be saved like the other attributes as columns on the database when you run migrations.

Answer 3

I am answering my own question here I found a solution to. Although, #property does work when rendering using a simple Django template when using React and rendering json responses validity is still not available.
In my serializers.py file I did the following...
class QuestionSerializer(serializers.ModelSerializer):
validity = serializers.ReadOnlyField()
class Meta:
model = Question
fields = '__all__'
Take away the #property from the models as it is no longer needed. This has worked for me and you can go to the Django rest_framework or test it in your React application to see if you have access to this.
I would like to know if there are any issues doing this and/or a better way. I was also trying to do validity = serializers.Field() instead of validity = serializers.ReadOnlyField() but got an error saying I needed a Field.to_representation() that takes in self, value as positional arguments.
What arguments exactly do I pass in here. I tried self, Question.validity and did not work. I am not sure what I am doing here.
As an update the method in the model I updated to...
def validity(self):
total_likes = self.likes + self.dislikes
if total_likes != 0:
return (self.likes / total_likes) * 100
else:
return 100
I did not notice before and does not really matter for the question but division by zero is not allowed being that by default division by zero will always occur.