django rest_framework ModelSerializerでカスタムフィールドを使用する

# models.py

class Monster(models.Model):
    first_name = models.CharField(max_length=255)
    last_name = models.CharField(max_length=255)

    @property
    def full_name(self):
        return self.first_name + self.last_name

class MonsterSerializer(serializer.ModelSerializer)
    class Meta:
        model = Monster
        readonly_fields = ("full_name)
    # sourceでプロパティ名入れる
    full_name = serializer.ReadOnlyField(source="full_name", read_only=True)