django asking to add default values

Question

I am new to django and I am facing some problem.

This was my previous model.

class Blog(models.Model):
    name = models.CharField(max_length=100)
    tagline = models.TextField()

I added some data to this model. After that I added one more field to it. Now my model looks like this..

class Blog(models.Model):
    name = models.CharField(max_length=100)
    tagline = models.TextField()
    age = models.IntegerField()

When I ran the command python manage.py makemigrations I got the following error which is obvious.

You are trying to add a non-nullable field 'age' to blog 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:

I don't want to add default so I deleted the table contents by accessing db.sqlite3

But again after running python manage.py makemigrations I am getting the same error.why?

Answer 1

Even though you have deleted the table, any changes to your Django model will always refer to the previous migration of that model, hence it still requires you to set a default value. If you're still in development, then you could delete the migrations for that model and then makemigrations again. But, this is terrible practice and you should never do this unless you are consciously squashing your models, the better way is to do what Django is telling you and set a default. This'll help in the long run anyways with error handling.

The other answers address how to set defaults quite well.