[Django]-Error in admin: __str__ returned non-string (type NoneType)

I had a similar issue. The problem was that the primary key for one row was null ( I dont know how that happened). I couldnt delete the row because of cascade issues. so I had to change the str mmethod to somthing like this.

def __str__(self):
    if self.customerName==None:
        return "ERROR-CUSTOMER NAME IS NULL"
    return self.customerName

Check out the class that you have referred to in

        models.ForeignKey 

The problem lies in the

        __str__() 

method of one of those classes.
Then, add

                             or ''

in the return statement of that class like this.

        def __str__(self):
            return self.title or ''

def __str__(self):
        return str(self.topic)

Use str to make it type string.
Then it’s not not-string type.

For this error you can use two solutions

first solution: you can comment it out below code

 def __str__(self):
    return self.id

to

 #def __str__(self):
 #  return self.id

secound solution: you can return the string from the object

 def __str__(self):
    return str(self.id)

that’s works for me:

    def __str__(self):
    return f"{self.category}"

Just use "f" string

You can also delete the instances in the model causing this problem from the django shell python manage.py shell . This helps when you are dealing with a model with lots of related models like mine.

Typically this problem is caused by altering model fields and
migrating, such that the instances are incompatible with each other
and related fields

If you are trying to use __str__() to return the value of a ForeignKey or a OneToOneField this would return error

Example:

def __str__():
    return self.user  # where user is a key to other model class

It should be:

def __str__():
    return self.user.__str__() 
    # Or basically any other way that would explicitly unbox the value inside the related model class.

In my case I had the same issue and its origin was that: for the field used in the __str__ functions, has null values saved in the data base.

So I can solve the issue doing somethings like this:

update table
set field_for_STR_use = 'any value'
where field_for_STR_use is null or field_for_STR_use = ''

after that, I only refreshed my view and the problem had disappeared.

There was one of the foreign reference which was returning non string field. I changed it to string field or you can change to str(foreign-key-return-element)
name = models.CharField(max_length=200, unique=True) # name of the article
parent = models.ForeignKey(‘self’,on_delete=models.DO_NOTHING,related_name=’category_parent_item’, default=None, null=True) # Store child items
created_at = models.DateTimeField(auto_now=True) # Creation date
updated_at = models.DateTimeField(auto_now=True) # Updation Date
user = models.ForeignKey(get_user_model(),

on_delete=models.DO_NOTHING,related_name=’category_update_user’, default=None, null=True) #User who updated the Article

def __str__(self):
    return self.name ----------> this was an integer field initially in foreign reference

In my case, I had a different model that was called by another one that had the default snippet from VSCode as:

def __str__(self):
    return

This was causing the error, even when it was showing in the log another place.

Toto_tico is right, although the above error can also occur when you fail to return a str property of your django model within the str(self) method:

Class model and(models.Model):
    Class Meta:
       verbose_name = "something"

    title = models.CharField(max_length=100)
    email = models.CharField(max_length=100)

    #Error instance:
    def __str__(self):
       self.title

    #Right way
    def __str__(self):
       return self.title

So it is highly advised to return the str property within the

def str(self)

method to avoid errors in the Django admin panel when trying to make changes to a particular data within a model table:

    def __str__(self):
       return self.property

I hope this will help someone.