python - Django:分配尚未创建的类的外键

Question

我有关系数据库，其中一个关系如下所示:

Student < --- > Major_enrollments

所以我需要在两个表中创建一个带有第二个表外键的列。鉴于事实，如果我定义类，例如首先是学生，我会收到这样的错误通知:“NameError: name 'Major_enrollments' is not defined”。

这是我写的一段代码(models.py):

class Students(models.Model):

    nr_album = models.IntegerField()
    fName = models.CharField(max_length=70)
    lName = models.CharField(max_length=70)
    pesel = models.BigIntegerField()
    address = models.CharField(max_length=100)
    major_enrollments = models.ForeignKey(Major_enrollments) #<---THAT DOESN'T WORK

    def __unicode__(self):
        return unicode(self.pesel)


    class Meta:
        db_table='Students'

class Major_enrollments(models.Model):
    majors = models.ForeignKey(Majors)
    students = models.ForeignKey(Students)

    def __unicode__(self):
        return unicode(self.id)

    class Meta:
        db_table='Major_enrollments'

Answer 1

您可以使用类名(作为字符串)而不是类本身:

class Students(models.Model):

    nr_album = models.IntegerField()
    fName = models.CharField(max_length=70)
    lName = models.CharField(max_length=70)
    pesel = models.BigIntegerField()
    address = models.CharField(max_length=100)
    major_enrollments = models.ForeignKey('Major_enrollments')

    def __unicode__(self):
        return unicode(self.pesel)


    class Meta:
        db_table='Students'