Why is Django setting default values to all existing model attributes?

Question

I have a model called Book. Book has the following attributes: title, release_date and condition where condition has a default value set to "new". I created some of Books in django admin site. After I created a new attribute for this model called category which it has a default value set to "No category". Why is django setting category = "new" to all existing books instead of "No category". With the books that I add after the migration Django set them correctly. Why is this happening.

class Book(models.Model):
class ConditionType(models.TextChoices):
    USED = "Used"
    NEW = "New"

class Category(models.TextChoices):
    ACTION_ADVENTURE = "Action and Adventure"
    CLASSIC = "Classic"
    MYSTERY = "Mystery"
    FANTASY = "Fantasy"
    HORROR = "Horror"
    LITERERY_FICTION = "Literary Fiction"
    SCIENCE_FICTION = "Science Fiction"
    NON_FICTION = "Non-Fiction"
    NO_CAT = "No category"

title = models.CharField(
    max_length=150,
    null=False,
)
release_date = models.DateField()
condition = models.CharField(
    max_length=12,
    choices=ConditionType.choices,
    default=ConditionType.NEW,
)
category = models.CharField(
    max_length=40,
    choices=Category.choices,
    default=Category.NO_CAT,
)

After the first migration I added the category field btw.

Answer 1

As far as I know, django needs some field value (as NULL) for the existing rows in database. Maybe you accidentally typed "new" when it asked you for filling those blank field values?