在表单中创建对象之前如何检查外键的详细信息？

Question

在我正在开发的Django项目中，有一个名为Course的模型，它包含许多Assignment对象。

这是models.py的一部分：

class Assignment(models.Model):
    course = models.ForeignKey(Course, related_name='get_assignments')
    name = models.CharField(max_length=200)
    ipaddress = models.CharField(null=True, max_length=500)
    publish_type = models.CharField(max_length=50, default="Scheduled")
    type_of_lab = models.CharField(max_length=50, default="Lab")
    timeduration = models.DurationField(default=timedelta(seconds=0), null=True)
    late_duration = models.DurationField(default=timedelta(seconds=0), null=True)
    exam_group_id = models.CharField(max_length=50, null=True)
    serial_number = models.IntegerField()
    program_language = models.CharField(max_length=32)
    duration = models.DurationField(default=timedelta(seconds=0), null=True)
    freezing_duration = models.DurationField(default=timedelta(seconds=0), null=True)
    deadline = models.DateTimeField(null=True)
    freezing_deadline = models.DateTimeField(null=True)
    publish_on = models.DateTimeField(null='true')
    bulk_add = models.FileField(max_length = 800,upload_to=assignment_bulk_upload_path, null=True)

通过表单创建分配时，将使用某些功能来验证表单。这是forms.py的一部分：

class AssignmentForm(forms.Form):
    assignment_type = forms.BooleanField(required=False, widget=forms.HiddenInput())
    name = forms.CharField(label="Assignment Name", widget=forms.TextInput(attrs={'placeholder':'Assignment Name (200 Characters or fewer)','maxlength':200}))
    Typeof = (('Lab', 'Lab'), ('Exam', 'Exam'))
    publishtype = (('Scheduled', 'Scheduled'), ('On Demand', 'On Demand'))
    publish_type = forms.ChoiceField(
        choices=publishtype,
        label="Choose type of Publish (Default : Scheduled)"
    )
    duration = forms.DurationField(
        label="Assignment Duration",
        required=False,
        help_text="Assignment Duration, input format is HH:MM:SS "
    )
    freezing_duration = forms.DurationField(
        label="Freezing extra time",
        required=False,
        help_text="Extra time for students to freeze submission, input format is HH:MM:SS "
    )
    bulk_add = forms.FileField(
        error_messages={'invalid': 'File was not a valid tar file.'},
        required=False,
        label="Add sections and/or test cases in bulk",     
)
    #
    #
    # some more code
    #
    #

    def clean_bulk_add(self):
        assig1 = self.cleaned_data['name']
        course1 = self.this_course
        user1 = course1.owner
        tot1 = 30 + len(str(user1)) + len(str(course1.title)) + len(str(assig1)) + len(str(self.cleaned_data['bulk_add']))
        if tot1 > 700 :
            raise forms.ValidationError("Assignment or Course name is too long: "+str(tot1))
        return self.cleaned_data['bulk_add']
    def clean_name(self):
        if not hasattr(self, 'this_course'):
            return self.cleaned_data['name']
        try:
            _ =Assignment.objects.filter(trash=False).get(name=self.cleaned_data['name'], course=self.this_course)
            raise forms.ValidationError('This assignment already exists in this course.')
        except Assignment.DoesNotExist:
            pass
       return self.cleaned_data['name']

正如您在验证AssignmentForm时所看到的，我想使用创建它的课程名称。因此，在函数clean_bulk_add中，我编写了course1 = self.this_course。

然后显示AttributeError 'AssignmentForm' object has no attribute 'this_course'。那么，如何获得要在其中创建作业的课程的名称？