CODEWITHSUNDEEP
pythondjangodjango-models
Harshit verma
Harshit verma

Reputation: 548

OnetoOne (primary_key=Tue) to ForeignKey in Django

I have a OnetoOne field with primary_key=True in a model. Now I want to change that to a ForeignKey but cannot since there is no 'id'.

From this:

user = models.OneToOneField(User, primary_key=True, on_delete=models.CASCADE)

To this:

user1 = models.ForeignKey(User, related_name='questionnaire', on_delete=models.CASCADE)

Showing this while makemigrations:

You are trying to add a non-nullable field 'id' to historicaluserquestionnaire without a default; we can't do that (the database needs something to populate existing rows). Please select a fix: 1) Provide a one-off default now (will be set on all existing rows with a null value for this column) 2) Quit, and let me add a default in models.py

So how to do that? Thanks!

Upvotes: 0

Views: 1299

Answers (3)

natehawkboss
natehawkboss

Reputation: 113

The problem is that your trying to remove the primary key, but Django is then going to add a new primary key called "id". This is non-nullable and unique, so you can't really provide a one-off default.

The easiest solution is to just create a new model and copy your table over in a SQL migration, using the old user_id to populate the id field. Be sure to reset your table sequence to avoid collisions.

Upvotes: 1

Hashir
Hashir

Reputation: 400

Django models have a default ID attribute. Since you changed the model, the previous data records has now conflicts with your new column attributes because when previous records were added, there were no ForeignKey. Remember, In your foreignkey, null values are not allowed. There are multiple fixes to your solution. Follow these step one-by-one and see what resolves your eror.

  • Delete your migrations file and run migrations again

Set NULL=True in your foreign key

OR

Delete previous records of the table to resolve the conflict, so that when you run migrations, it adds a default value of id itself

instead of deleting, you can also try and change your migrations files directly like this

https://stackoverflow.com/a/29074241/11979793

Upvotes: 1

Subham Subhasis Patra
Subham Subhasis Patra

Reputation: 131

just delete your previous migrations 

e.g 

    migrations:
          |
          |- 001.initail.py
          |- 002.examplefiles.py

you just have to delete you most recent migrations and

run the command

python3 manage.py makemigrations
python3 manage.py migrate

Upvotes: 1

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