Django Generic Relations - Object of Type ** is Not JSON Serializable

Question

Still new to Django so bear with me.

I am trying to follow Django example https://docs.djangoproject.com/en/2.2/ref/contrib/contenttypes/.

I am trying to use tests.py to create notes for student 1.

Here is tests.py:

from django.test import TestCase
from gsndb.models import *
from django.contrib.contenttypes.models import ContentType
from django.contrib.auth.models import User

# Create your tests here.

student = Student.objects.get(id=4)
text = "The student is content"
user = User.objects.get(id=2)

new_note = Note(text=text, content_object = student, user = user)

new_note.save()

I am wanting this to create a note for student 1. However when I run the test, I get this error:

Object of type 'Student' is not JSON serializable

Here is the traceback:

Environment:


Request Method: GET
Request URL: http://localhost/gsndb/note/

Django Version: 2.1.7
Python Version: 3.6.8
Installed Applications:
['django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'corsheaders',
 'rest_framework',
 'user_app.apps.UserAppConfig',
 'gsndb.apps.GsndbConfig']
Installed Middleware:
['corsheaders.middleware.CorsMiddleware',
 'django.middleware.security.SecurityMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware']



Traceback:

File "/usr/lib/python3.6/site-packages/django/core/handlers/exception.py" in inner
  34.             response = get_response(request)

File "/usr/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
  156.                 response = self.process_exception_by_middleware(e, request)

File "/usr/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
  154.                 response = response.render()

File "/usr/lib/python3.6/site-packages/django/template/response.py" in render
  106.             self.content = self.rendered_content

File "/usr/lib/python3.6/site-packages/rest_framework/response.py" in rendered_content
  72.         ret = renderer.render(self.data, accepted_media_type, context)

File "/usr/lib/python3.6/site-packages/djangorestframework_camel_case2/render.py" in render
  9.                                                          **kwargs)

File "/usr/lib/python3.6/site-packages/rest_framework/renderers.py" in render
  107.             allow_nan=not self.strict, separators=separators

File "/usr/lib/python3.6/site-packages/rest_framework/utils/json.py" in dumps
  28.     return json.dumps(*args, **kwargs)

File "/usr/lib/python3.6/json/__init__.py" in dumps
  238.         **kw).encode(obj)

File "/usr/lib/python3.6/json/encoder.py" in encode
  199.         chunks = self.iterencode(o, _one_shot=True)

File "/usr/lib/python3.6/json/encoder.py" in iterencode
  257.         return _iterencode(o, 0)

File "/usr/lib/python3.6/site-packages/rest_framework/utils/encoders.py" in default
  68.         return super(JSONEncoder, self).default(obj)

File "/usr/lib/python3.6/json/encoder.py" in default
  180.                         o.__class__.__name__)

Exception Type: TypeError at /gsndb/note/
Exception Value: Object of type 'Student' is not JSON serializable

Here is models.py

class Note(models.Model):
    user = models.ForeignKey(
        get_user_model(),
        on_delete = models.PROTECT,
    )
    created = models.DateTimeField(default = timezone.now)
    text = models.TextField()

    # Below the mandatory fields for generic relation
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('content_type','object_id')

class Student(models.Model):
    current_school = models.ForeignKey(
        "School",
        null = True,
        on_delete = models.PROTECT,
    )
    current_program = models.ForeignKey(
        "Program",
        null = True,
        on_delete = models.PROTECT,
    )
    first_name = models.CharField(max_length = 35, blank=True)
    last_name = models.CharField(max_length = 35, blank=True)
    middle_name = models.CharField(max_length = 35, blank=True)
    """Establish choices for Gender"""
    GENDER_CHOICES = (
        ("M", 'Male'),
        ("F", 'Female'),
        ("NB", 'NonBinary'),
    )
    gender = models.CharField(
            max_length = 2,
            blank = True,
            choices = GENDER_CHOICES,
    )
    birth_date = models.DateField(null = True)
    state_id = models.BigIntegerField(null = True)
    """Establish choices for Grade Year"""
    GRADE_YEAR_CHOICES = (
        (0, 'Kindergarten'),
        (1, 'First Grade'),
        (2, 'Second Grade'),
        (3, 'Third Grade'),
        (4, 'Fourth Grade'),
        (5, 'Fifth Grade'),
        (6, 'Sixth Grade'),
        (7, 'Seventh Grade'),
        (8, 'Eighth Grade'),
        (9, 'Ninth Grade'),
        (10, 'Tenth Grade'),
        (11, 'Eleventh Grade'),
        (12, 'Twelfth Grade'),
    )
    grade_year = models.SmallIntegerField(
        choices = GRADE_YEAR_CHOICES,
        null = True,
    )
    reason_in_program = models.TextField(blank=True)
    notes = GenericRelation(Note)

Here is serializers.py:

class NoteSerializer(serializers.ModelSerializer):
    class Meta:
        model = Note
        fields = ("user",
            "created",
            "text",
            "content_type",
            "object_id",
            "content_object")

class StudentSerializer(serializers.BaseSerializer):

        def to_representation(self, student_obj):
            notes = NoteSerializer(many = True)
            notes_json = notes.data

            return {
                "current_school": student_obj.current_school.id,
                "current_program": student_obj.current_program.id,
                "first_name": student_obj.first_name,
                "last_name": student_obj.last_name,
                "middle_name": student_obj.middle_name,
                "gender": student_obj.gender,
                "birth_date": student_obj.birth_date,
                "state_id": student_obj.state_id,
                "grade_year": student_obj.grade_year,
                "reason_in_program": student_obj.reason_in_program,
                "notes": notes_json,
            }

Here is my views.py:

class NoteList(generics.ListCreateAPIView):
    queryset = Note.objects.all()
    serializer_class = NoteSerializer

Thanks for your time!

Answer 1

Figured out my problem. It was in my views.

My view was

class NoteSerializer(serializers.ModelSerializer):
    class Meta:
        model = Note
        fields = ("user",
            "created",
            "text",
            "content_type",
            "object_id",
            "content_object")

I needed to remove "content_object" because it wasn't JSON serializable. It needed to look like this:

class NoteSerializer(serializers.ModelSerializer):
    class Meta:
        model = Note
        fields = ("user",
            "created",
            "text",
            "content_type",
            "object_id")

Thanks for all the help!