python之Django:分配尚未创建的类的外键

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' 

请您参考如下方法:

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'