I have a method generate_certificate(), that uses a base image from default storage in django and edits it through pillow library and saves that image to the default djnago storage and returns file path.

def generate_certificate(name, certification):
    base_image_path = os.path.join(settings.MEDIA_ROOT, 'certificates', 'Certificate.png')
    font_path = os.path.join(settings.MEDIA_ROOT, 'fonts', 'font.ttf')

    if not os.path.exists(base_image_path):
        raise FileNotFoundError(f"Base certificate image not found at {base_image_path}")

    img = Image.open(base_image_path)
    d = ImageDraw.Draw(img)

    location = (143, 155)
    text_color = (100, 100, 100)
    font = ImageFont.truetype(font_path, 40)
    d.text(location, name, fill=text_color, font=font)

    location = (360, 215)
    font = ImageFont.truetype(font_path, 18)
    d.text(location, certification, fill=text_color, font=font)

    location = (200, 310)
    font = ImageFont.truetype(font_path, 15)
    d.text(location, '2024-08-07', fill=text_color, font=font)

    file_name = f"{name.split(' ')[0]}_{random.randint(0, 255)}.png"
    file_stream = BytesIO()
    img.save(file_stream, format='PNG')
    file_stream.seek(0)

    # Save the file to the media directory and return the relative path
    file_path = default_storage.save(f'certificates/{file_name}', ContentFile(file_stream.read()))

    return file_path  # Return the relative path

I am using this method in a post method view that creates a record for UserCertification model. The request payload has the all the data except the image which is generated in the view. as below:

def post(self, request):
try:

user = request.data.get('user')
certification = request.data.get('certification')
score = request.data.get('score')

            certificate_url = generate_certificate(user, certification)
            print(f"Generated certificate file path: {certificate_url}")  # Debugging
            data = {
                'user': user,
                'certification': certification,
                'score': score,
                'certificate': certificate_url,
            }
            serializer = UserCertificationSerializer(data=data)
    
            if serializer.is_valid():
                serializer.save()
                print(serializer.data)
                return Response(serializer.data, status=HTTP_201_CREATED)
            else:
                return Response({"message": "Invalid Json"}, status=HTTP_400_BAD_REQUEST)
        except Exception as e:
            return Response({"message": str(e)}, status=HTTP_400_BAD_REQUEST)

So when i hit the api through postman the postman returns null in the certificate field instead of the url of the file as shown below however when i use django admin to add user certification that correctly saves the file on the server and also fills the certification field with the correct url.

{
    "user": 6,
    "certification": 8,
    "score": "90.00",
    "certificate": null,
    "completion_date": "2024-08-09"

}

The serilizer and the model is :

class UserCertification(models.Model):
    user = models.ForeignKey(User,on_delete=models.CASCADE)
    certification = models.ForeignKey(Certification,on_delete=models.CASCADE)
    score = models.DecimalField(decimal_places=2,max_digits=4)
    certificate = models.ImageField(upload_to='certificates/', null=True)
    completion_date = models.DateField(default=date.today)
    
    class Meta:
        unique_together = ('user', 'certification')

class UserCertificationSerializer(serializers.ModelSerializer):
    certificate = serializers.SerializerMethodField()

    class Meta:
        model = UserCertification
        fields = ['user', 'certification', 'score', 'certificate', 'completion_date']
    
    def get_certificate(self, obj):
        if obj.certificate:
            url = obj.certificate.url
            print(f"Certificate URL: {url}")  # Debugging
            return url
        print("Certificate URL is None")  # Debugging
        return None

I am expecting that when i hit the api though postman the certificate field should be filled with url of the saved file that is generated through the generate_certificate method.

I am guessing that there is a problem with the return value of the generate_certificate method as when the serializer is run it prints: Certificate URL is None

But cant figure it out.`

I tried this post Save a generated PIL image into an ImageField in django as well but could not figure out.