相关疑难解决方法(0)

作为这个问题的后续内容,我想确定正在发生的实际错误.我做错了什么,或者这是一个错误？

    f = {'groups__isnull': 'True'}
    students1 = models.Student.objects.filter( **f )
    students2 = models.Student.objects.filter(groups__isnull=True)

这两个查询应该相同,但不是.

作为参考,我的模型:

class Student (models.Model):
    user = models.ForeignKey(User, unique=True, null=False, related_name='student')
    teacher = models.ForeignKey(User, null=False, related_name='students')
    assignment = models.ForeignKey(LabJournal, blank=True, null=True, related_name='students')

class JournalGroup (models.Model):
    title = models.CharField(null=False, max_length=256)
    owner = models.ForeignKey(User, null=True, related_name='journal_groups')
    members = models.ManyToManyField(Student, blank=True, related_name='groups')