I am making a notes app. When I try to create a foreign key to link the user and its notes, im getting an error while using

python manage.py migrate

. I am very new to foreign keys, I looked at the Django docs, this is how they created a foreign key.

here's the code :

from django.db import models

class User(models.Model):
    username = models.CharField(max_length=50)
    email = models.EmailField(max_length=50)



class Note(models.Model):
    body = models.TextField(null=True, blank=True)
    updated = models.DateTimeField(auto_now=True)
    created = models.DateTimeField(auto_now_add=True)
    author = models.ForeignKey(User, on_delete=models.CASCADE)


    def __str__(self):
        return self.body[0:50]

here's the error :

django.db.utils.IntegrityError: NOT NULL constraint failed: new__api_note.author_id

CodePudding user response：

Your issue is that that there are existing notes in the database that do not have a author_id field, but you have not set a default value and neither allowed to to be kept blank. Thus it's a IntegrityError to add the field.

You can solve this in 2 ways:

Allow the field to be blank

1. Delete the last migration in your migrations folder
2. Edit the author field like this:

author = models.ForeignKey(User, on_delete=models.CASCADE, null=True)

3. Run makemigrations and migrate

Set a default value for the field

1. Delete the last migration from the migrations folder. You can also edit it but simply deleting it is easiest
2. Run makemigrations again
3. During make migration, it will prompt you if you want to provide a default value for the field. Select "Provie a one of value for now"
4. Type models.User.objects.all().first() or alternatively some other "defalt" author for existing notes
5. Run migrate

You can also solve the problem by removing all existing notes from the database