In Django REST Framework, a ModelSerializer typically maps model fields to serializer fields automatically. But what if you want to include a computed or dynamic value that isn’t a direct field on your model?

That’s where SerializerMethodField comes in.

What is SerializerMethodField?

SerializerMethodField is a read-only field that gets its value by calling a method on the serializer class. This method lets you compute or customize a value at runtime based on the serialized object or request context.

It’s perfect for:

• Custom computed fields

• Conditional data

• Related model logic

Syntax

from rest_framework import serializers

class MySerializer(serializers.ModelSerializer):
    custom_field = serializers.SerializerMethodField()

    class Meta:
        model = MyModel
        fields = ['id', 'name', 'custom_field']

    def get_custom_field(self, obj):
        return obj.name.upper()

• The method name must be get_<field_name>

• The method receives the instance (obj) being serialized

Example: Book and Author

models.py

class Author(models.Model):
    name = models.CharField(max_length=100)

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.ForeignKey(Author, on_delete=models.CASCADE)
    pages = models.IntegerField()

serializers.py

class BookSerializer(serializers.ModelSerializer):
    author_name = serializers.SerializerMethodField()
    is_lengthy = serializers.SerializerMethodField()

    class Meta:
        model = Book
        fields = ['title', 'author_name', 'pages', 'is_lengthy']

    def get_author_name(self, obj):
        return obj.author.name

    def get_is_lengthy(self, obj):
        return obj.pages > 300

Sample Output

{
  "title": "Django Mastery",
  "author_name": "Jane Austen",
  "pages": 350,
  "is_lengthy": true
}

Using Context in SerializerMethodField

You can also access the serializer context, such as the request user.

class BookSerializer(serializers.ModelSerializer):
    is_favorite = serializers.SerializerMethodField()

    class Meta:
        model = Book
        fields = ['title', 'is_favorite']

    def get_is_favorite(self, obj):
        user = self.context['request'].user
        return obj in user.favorite_books.all()

When instantiating the serializer:

BookSerializer(book_instance, context={'request': request})

Nested Use Case

class AuthorSerializer(serializers.ModelSerializer):
    book_count = serializers.SerializerMethodField()

    class Meta:
        model = Author
        fields = ['id', 'name', 'book_count']

    def get_book_count(self, obj):
        return obj.book_set.count()

This will return how many books the author has written, even though book_count isn't a model field.

✅ Benefits

⚠️ Common Pitfalls

Advanced Example: Conditional Discount

class ProductSerializer(serializers.ModelSerializer):
    discount_price = serializers.SerializerMethodField()

    class Meta:
        model = Product
        fields = ['name', 'price', 'discount_price']

    def get_discount_price(self, obj):
        user = self.context['request'].user
        if user.is_staff:
            return obj.price * 0.8
        return obj.price

Full Working Example

models.py

class Book(models.Model):
    title = models.CharField(max_length=100)
    pages = models.IntegerField()
    published_date = models.DateField()

serializers.py

class BookSerializer(serializers.ModelSerializer):
    is_new_release = serializers.SerializerMethodField()

    class Meta:
        model = Book
        fields = ['title', 'pages', 'published_date', 'is_new_release']

    def get_is_new_release(self, obj):
        from datetime import date, timedelta
        return obj.published_date >= date.today() - timedelta(days=30)

Output

{
  "title": "Learn Django",
  "pages": 250,
  "published_date": "2025-05-01",
  "is_new_release": true
}

Best Practices

✅ Summary

Conclusion

SerializerMethodField is a powerful feature in Django REST Framework that allows you to expose custom, dynamic, or computed fields without cluttering your models. Use it when you need flexibility in what your serializers output—whether it’s user-specific logic, conditional formatting, or extra metadata.