CODEWITHSUNDEEP
pythondjangopython-3.xlinuxdjango-models
M.J
M.J

Reputation: 325

Error in models, TypeError: on_delete must be callable

When I run the following command:

python manage.py makemigrations

I have this error:


  File "/home/user/project/myvirt/forum/boards/models.py", line 9, in <module>
    class Topic(models.Model):
  File "/home/user/project/myvirt/forum/boards/models.py", line 12, in Topic
    board = models.ForeignKey(Board, related_name='topics', on_delete='cascade')
  File "/usr/local/lib/python3.7/dist-packages/django/db/models/fields/related.py", line 801, in __init__
    raise TypeError('on_delete must be callable.')
TypeError: on_delete must be callable.

My models.py content is:


from django.db import models
from django.contrib.auth.models import User
# Create your models here.

class Board(models.Model):
    name = models.CharField(max_length=30, unique=True)
    description = models.CharField(max_length=100)

class Topic(models.Model):
    subject = models.CharField(max_length=255)
    last_updated = models.DateTimeField(auto_now_add=True)
    board = models.ForeignKey(Board, related_name='topics', on_delete='cascade')
    creator = models.ForeignKey(User, related_name='topics', on_delete='cascade')

class Post(models.Model):
    message = models.TextField(max_length=4000)
    topic = models.CharField(Topic, related_name='posts', on_delete='cascade')
    created_by = models.CharField(User, related_name='posts', on_delete='cascade')
    created_at = models.DateTimeField(auto_now_add=True)
    updated_by = models.CharField(User, related_name='posts', on_delete='cascade')
    updated_at = models.DateTimeField(null=True)

This is an exercise in sample forum and seems to be a problem with on_delete='cascade'.

Update:

I am using Django version 3.

Upvotes: 0

Views: 727

Answers (2)

tangrwx
tangrwx

Reputation: 46

The error message on_delete must be callable indicates that it should be callable instead of string.

Following the Django official documentation ForeignKey, and here is a example:

from django.db import models

class Car(models.Model):
    manufacturer = models.ForeignKey(
        'Manufacturer',
        on_delete=models.CASCADE,
    )

Upvotes: 1

wfehr
wfehr

Reputation: 2225

The problem is that in your model fields you are assigning a string for on_delete. (-> `on_delete='cascade')

What you need to do is to assign (as the error tells you) a callable, like CASCADE.

Example:

from django.db import models

class MyModel(models.Model):
    my_relation = models.ForeignKey(
        MyOtherModel,
        on_delete=models.CASCADE,
    )
    ...

Furthermore: You are setting related_name=XYZ on all your fields. This is incorrect, because a related_name can only be assigned to fields which handle relations, like ForeignKey.

Also see docs.

Upvotes: 2

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