CODEWITHSUNDEEP
pythondjangodjango-modelsnullfield
user3182532
user3182532

Reputation: 1127

Django: non-nullable field without a default

In Django I use manage.py makemigrations and manage.py migrate on the following models.py file:

class Family(models.Model):
    comment1 = models.CharField(max_length=80)
    #comment2 = models.CharField(max_length=80)

After this successful initialization, I changed models.py to (I just uncomment the new model field which is basically a copy of the other model field):

class Family(models.Model):
    comment1 = models.CharField(max_length=80)
    comment2 = models.CharField(max_length=80)

Now when I try to makemigrations again I get the following error:

You are trying to add a non-nullable field 'comment' to family 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 Select an option:

Why didn't I get this error upon intialization in the first place?

Upvotes: 4

Views: 9236

Answers (6)

Andrii
Andrii

Reputation: 1

Just select option 1. Then set a default. It will create a migration script with the property preserve_default=False which means the default is used only for the migration. It will not affect the default settings in the database.

https://docs.djangoproject.com/en/4.2/ref/migration-operations/#alterfield

Upvotes: 0

Reza Hamzenejad
Reza Hamzenejad

Reputation: 1

You can add this: default=None or default="something" or add null=True, blank=True.

Upvotes: -1

joe-khoa
joe-khoa

Reputation: 610

I have faced a same issue, in my case:

Focus on the alert:

...non-nullable field 'comment' to family...

  • model: Family
  • field: comment

Just add one more attr in the field comment of the model family:

default=''

Upvotes: 0

arpit shukla
arpit shukla

Reputation: 31

image1=models.ImageField(upload_to='app/image12',help_text="hi", null=True)

That is, set null= True'in the field.

It happens when you change your model after stored database.

Upvotes: 3

Mehrdad Pedramfar
Mehrdad Pedramfar

Reputation: 11073

Others are right. you should set a default value for that field. but there is a a trick that you can solve this. but it is not a good way... only if you have no choice.
1. comment all of your table
2. run makemigrations and migrate
3. uncomment your table
4.2. run makemigrations and migrate again

Upvotes: 3

Anurag Meena
Anurag Meena

Reputation: 166

If you want to make it non nullable without default. you have to provide value for the same field when you create migration file. thats why it asks for the option. type "1" in terminal while python manage.py makemigrations and then provide a value for the field for previously saved row(if any).

Let me know if this helps.

Upvotes: 0

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