django: related field has invalid lookup

I have the following models

class SchoolClass(models.Model):
    id = models.AutoField(primary_key = True)
    class_name = models.TextField()
    level = models.IntegerField()
    taught_by = models.ManyToManyField(User,related_name="teacher_teaching",through='TeachSubject')
    attended_by = models.ManyToManyField(User,related_name='student_attending',through='StudentClassHistory')

    def __unicode__(self):
        return self.class_name
    class Meta:
        db_table = 'classes'

class StudentClassHistory(models.Model):
    student = models.ForeignKey(User)
    year = models.IntegerField(default=datetime.date.today().year)
    semester = models.In开发者_C百科tegerField()
    attended_class  = models.ForeignKey(SchoolClass) 

    class Meta:
        db_table = 'student_class_history'

When i try to run the following query

User.objects.filter(student_attending__studentclasshistory__year=2011)

i got the error Related Field has invalid lookup: year. That's strange, because i omitted year and the available fields are Cannot resolve keyword '' into field. Choices are: attended_class, id, semester, student, year

How is this so?

Also, with through in my model attribute, can I just remove related_name?

The problem is that year is a field lookup, so Django thinks you're trying to extract the year from something which isn't a date. You should write:

User.objects.filter(student_attending__studentclasshistory__year__exact=2011)

(Also, you ought to make the default for year a callable, i.e.:

year = models.IntegerField(default=lambda: datetime.date.today().year)

)