ForeignKey的NOT NULL约束失败（NULL=True）

Question

我有两个模型，即Applicant和LoanRequest。每当创建Applicant实例时，就会向进行API调用的函数发送一个信号。来自调用的数据以及发送信号的实例的主键被保存为LoanRequest

但是，当我保存LoanRequest时，会出现以下错误：

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

这是我的密码：

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"])

非常新的Django，将非常感谢帮助

Answer 1

LoanRequest有一个字段

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

由于dealer_id没有null=True，因此在不提供dealer_id的情况下创建LoanRequest实例将引发数据库错误

您需要在LoanRequest的实例化中提供一个dealer_id，它应该是一个Dealer实例，或者更改LoanRequest模型，以便dealer_id字段具有null=True

请参阅上面的评论：在Django模型外键上使用后缀_id，这样做几乎总是不正确的

Answer 2

指定blank=True而不指定null=True对于ForeignKey不是很有用

改用这个：

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

这将使该字段成为可选字段。否则，每次创建LoanRequest时都必须指定Dealer