from_db_value() takes 4 positional arguments but 5 were given Django

user_7949229 0
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i have simple django notification table with the following structure

+-------------------------------+--------------+------+-----+---------+----------------+
| Field                         | Type         | Null | Key | Default | Extra          |
+-------------------------------+--------------+------+-----+---------+----------------+
| id                            | int(11)      | NO   | PRI | NULL    | auto_increment |
| level                         | varchar(20)  | NO   |     | NULL    |                |
| unread                        | tinyint(1)   | NO   |     | NULL    |                |
| actor_object_id               | varchar(255) | NO   |     | NULL    |                |
| verb                          | varchar(255) | NO   |     | NULL    |                |
| description                   | longtext     | YES  |     | NULL    |                |
| target_object_id              | varchar(255) | YES  |     | NULL    |                |
| action_object_object_id       | varchar(255) | YES  |     | NULL    |                |
| timestamp                     | datetime(6)  | NO   |     | NULL    |                |
| public                        | tinyint(1)   | NO   |     | NULL    |                |
| action_object_content_type_id | int(11)      | YES  | MUL | NULL    |                |
| actor_content_type_id         | int(11)      | NO   | MUL | NULL    |                |
| recipient_id                  | int(11)      | NO   | MUL | NULL    |                |
| target_content_type_id        | int(11)      | YES  | MUL | NULL    |                |
| deleted                       | tinyint(1)   | NO   |     | NULL    |                |
| emailed                       | tinyint(1)   | NO   |     | NULL    |                |
| data                          | longtext     | YES  |     | NULL    |                |

And all what i want is to fetch the content so this is my view

@api_view(['GET'])
@login_required()
def getnotifications(request, page):

    try:
        if page == None:
            page = 1

        userID = request.user
        unreadnum = Notification.objects.filter(recipient=request.user,
                                                unread=True).count()
        notifs = Notification.objects.filter(recipient=userID, unread=True).distinct().order_by(
            '-timestamp')
        print("got ntifs")
        paginator = Paginator(notifs, 10)
        paginatednotifs = paginator.page(page)
        return Response(
            {"notifications": NotificationSerializer(paginatednotifs,many=True, context={"user": request.user}).data,
             "unread": unreadnum,"has_next":paginatednotifs.has_next()})


    except Exception as e:
        print("========")
        print(str(e))
        return Response(
            {"notifications": str(e)})

and thus view's serilizer is like this :

class NotificationSerializer(serializers.ModelSerializer):
    actor = serializers.SerializerMethodField()
    target = serializers.SerializerMethodField()

    class Meta:
        model = Notification
        fields = ("id","actor", "target","timestamp","verb")

    def get_actor(self,obj):
        user = Useraccount.objects.get(user__id=obj.actor_object_id)
        return UserAccountSerializer(user,many=False,context={"user":self.context["user"]}).data

    def get_target(self,obj):

        if obj.target_content_type.model == "action":

            action = ActstreamAction.objects.get(id=obj.target_object_id)
            return ActionNotificationSerializer(action,many=False).data
        return {"targetType":obj.target_content_type.model,"action":obj.action_object_content_type.model}

i tried to make many modifications in the serilizer and the view but always and always the same error

from_db_value() takes 4 positional arguments but 5 were given

i couldn't find this from_db_value() function i'm really having a hard time with this problem, and i know just the basics about Django

i'm using

  • django : 1.11.18
  • djangorestframework : 3.6.4
  • mysql : 5.7.25

A traceback for the error:

Traceback (most recent call last):
  File "<homedir>/project/webServer/app/myNotifications/views.py", line 66, in getnotifications
    {"notifications": NotificationSerializer(paginatednotifs,many=True, context={"user": request.user}).data,
  File "<homedir>/virtualenv/lib/python3.6/site-packages/rest_framework/serializers.py", line 739, in data
    ret = super(ListSerializer, self).data
  File "<homedir>/virtualenv/lib/python3.6/site-packages/rest_framework/serializers.py", line 263, in data
    self._data = self.to_representation(self.instance)
  File "<homedir>/virtualenv/lib/python3.6/site-packages/rest_framework/serializers.py", line 657, in to_representation
    self.child.to_representation(item) for item in iterable
  File "<homedir>/virtualenv/lib/python3.6/site-packages/rest_framework/serializers.py", line 657, in <listcomp>
    self.child.to_representation(item) for item in iterable
  File "/usr/lib/python3.6/_collections_abc.py", line 883, in __iter__
    v = self[i]
  File "<homedir>/virtualenv/lib/python3.6/site-packages/django/core/paginator.py", line 145, in __getitem__
    self.object_list = list(self.object_list)
  File "<homedir>/virtualenv/lib/python3.6/site-packages/django/db/models/query.py", line 250, in __iter__
    self._fetch_all()
  File "<homedir>/virtualenv/lib/python3.6/site-packages/django/db/models/query.py", line 1121, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
  File "<homedir>/virtualenv/lib/python3.6/site-packages/django/db/models/query.py", line 62, in __iter__
    for row in compiler.results_iter(results):
  File "<homedir>/virtualenv/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 847, in results_iter
    row = self.apply_converters(row, converters)
  File "<homedir>/virtualenv/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 832, in apply_converters
    value = converter(value, expression, self.connection, self.query.context)
TypeError: from_db_value() takes 4 positional arguments but 5 were given
django-rest-framework django
2 Answers

TL;DR:

Most likely, jsonfield package is not incompatible with Django==1.11.18

Details:

You are using Django in version 1.11.18, which requires 5 positional arguments for from_db_value method and do not support JSONFields.

You are also using django-notifications package, which internally uses jsonfield>=1.0.3 package. Since there is no max. version set, django-notifications uses the newest version of jsonfield package.

The newest versions of jsonfield (3.0.0 and higher) doesn't support Django below 2.2. One of the reasons is that it takes only 4 arguments instead of 5.

The highest version of jsonfield that supports Django 1.11 is jsonfield==2.1.1

Please check the version of installed jsonfield package (use grep only if you're on unix sytem):

pip freeze | grep jsonfield

If it's 3.0.0 or more, you may try to downgrade it to 2.1.1. Be aware that it may (or may not) cause other compatibility issues with other packages.

user_57117330

I got the same error:

  File "/home/django/lee3/lib/python3.8/site-packages/django/db/models/sql/compiler.py", line 833, in apply_converters
    value = converter(value, expression, self.connection, self.query.context)
TypeError: from_db_value() takes 4 positional arguments but 5 were given

The 'from_db_value' it was complaining about was in /picklefield/fields.py.

Changed line 184: def from_db_value(self, value, expression, connection): to: def from_db_value(self, value, expression, connection, context=None): Everything works fine now.

user_142906890
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