Filtering Foreign Key Based on Another SlugRelatedField in POST Requests in Django Rest Framework

userciZl 0
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I'm using Django Rest Framework and have a model with multiple ForeignKey relationships and am POSTing their slugs rather than id. The issue is that the second ForeignKey requires a queryset that is filtered based on the first. Here is a not-so-perfect example:

# models.py
class Student(models.Model):
    slug = models.SlugField(...)

class Class_(models.Model):
    slug = models.SlugField(...)

class ReportCard(models.Model)
    student = models.ForeignKey(Student)
    class_ = models.ForeignKey(Class_)
    grade = models.CharField(...)

# serializers.py
class ReportCardSerializer(serializers.ModelSerializer):
    student = serializers.SlugRelatedField(queryset=models.Student.objects.all(), slug_field='slug')
    class_ = serializers.SlugRelatedField(queryset=models.Class_.objects.filter(???), slug_field='slug')  # need to filter based on student here

    class Meta:
        model = models.ReportCard
        fields = '__all__'  # use all fields

How do I do this? student in the serializer does not return the model and I don't know how to access the data inside of ReportCardSerializer to grab the string from the POST request to manually filter class_.

django-rest-framework django python
1 Answers

in your case, you don't need to validate in a get request, it's enough validating in a post request so override validate method:

class ReportCardSerializer(serializers.ModelSerializer):
    student = serializers.SlugRelatedField(queryset=models.Student.objects.all(), slug_field='slug')
    class_ = serializers.SlugRelatedField(queryset=models.Class_.objects.all(), slug_field='slug')

    class Meta:
        model = models.ReportCard
        fields = '__all__'

    def validate(self, data):
        student = data.get('student')
        class_ = data.get('class_')

        if check class_ is valid for the student, if not raise error:
            raise serializers.ValidationError("class_ is invalid")
        return data
Mukhtor0
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