django中model文件中外键怎么设置默认值为空?
class Book(models.Model): name = models.CharField(max_length=10) pub_date = models.DateField() classification = models.ForeignKey(Classification, on_delete=models.DO_NOTHING, null=True) student = models.ForeignKey(Student, on_delete=models.DO_NOTHING, null=True) author = models.CharField(max_length=8) content = models.CharField(max_length=50) |
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