ForeignKey 的 NOT NULL 约束失败（null=True）

Question

I have two models, namely Applicant and LoanRequest . Whenever an Applicant instance is created, a signal is sent to a function that makes an API call. The data from the call, along with the primary key of the instance that sent the signal, is saved to as a LoanRequest .

When I save the LoanRequest , however, it gives the following error:

django.db.utils.IntegrityError: NOT NULL constraint failed: queues_loanrequest.dealer_id_id

Here's my code:

class Applicant(models.Model):
    app_id = models.CharField(max_length=100)
    first_name = models.CharField(max_length=100)
    last_name = models.CharField(max_length=100)
    email = models.CharField(max_length=100)
    date_posted = models.DateTimeField(default=timezone.now)

    def __str__(self):
        return self.first_name + " " + self.last_name


class LoanRequest(models.Model):
    loan_request_id = models.CharField(max_length=100)
    app_id = models.ForeignKey(Applicant, on_delete=models.CASCADE)
    FICO_score = models.CharField(max_length=100)
    income_risk_score = models.CharField(max_length=100)
    DTI = models.CharField(max_length=100)
    date_requested = models.DateTimeField(default=timezone.now)
    loan_request_status = models.CharField(max_length=100,blank=True)
    dealer_id = models.ForeignKey(Dealer, on_delete=models.CASCADE,blank=True)

def credit_check(sender, instance, **kwargs):
    credit_json = get_credit(instance.pk) #credit information for applicant
    credit_json = json.loads(credit_json)
    new_request = LoanRequest.objects.create(app_id=instance, FICO_score=credit_json["ficco-score"],
                                income_risk_score=credit_json["income-risk-score"],
                               DTI=credit_json["DTI"])

Very new to Django, would greatly appreciate help!

Answer 1

LoanRequest has a field

dealer_id = models.ForeignKey(Dealer, on_delete=models.CASCADE,blank=True)

Because dealer_id doesn't have null=True , creating a LoanRequest instance without supplying a dealer_id will raise the database error you've got.

You need to either supply a dealer_id in the instantiation of the LoanRequest , which should be a Dealer instance, or else change your LoanRequest model so that the dealer_id field has null=True .

Please see comment above re: using the suffix _id on a Django model foreign key - it's nearly always incorrect to do so.

Answer 2

Specifying blank=True without null=True is not very useful for a ForeignKey.

Use this instead:

dealer_id = models.ForeignKey(Dealer, on_delete=models.CASCADE, blank=True, null=True) 

This would make the field optional. Otherwise, you would have to specify the Dealer every time you create a LoanRequest .