Can I make the foreign key field optional in Django model

Question

I have this code

subject      = models.ForeignKey(subjects)
location     = models.ForeignKey(location)
publisher    =  models.ForeignKey(publisher)

There its not always possible that I have three values of books. so sometimes if I don't know subject or location, or publisher. Then I want to keep them empty

But if I have then I need select box to select. is it possible like that

Answer 1

In order to accomplish this, the on_delete argument is necessary along with blank=True and null=True, and it would be better if you do it this way.

subject = models.ForeignKey(subjects, on_delete=models.SET_NULL, blank=True, null=True)

Answer 2

null=True

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subject=models.ForeignKey(subjects, on_delete=models.CASCADE, default=None, blank=True, null=True)

Field.null

If True, Django will store empty values as NULL in the database. Default is False.

Avoid using null on string-based fields such as CharField and TextField. If a string-based field has null=True, that means it has two possible values for “no data”: NULL, and the empty string. In most cases, it’s redundant to have two possible values for “no data;” the Django convention is to use the empty string, not NULL. One exception is when a CharField has both unique=True and blank=True set. In this situation, null=True is required to avoid unique constraint violations when saving multiple objects with blank values.