python之Django-Models:TypeError:强制转换为 Unicode:需要字符串或缓冲区，用户发现

我要显示值

(last name and first name)

作为外键来自模型。我希望这些值以选择的形式出现，以便用户可以选择他们想要将对象分配给的学生的姓名。

比如我有student form和Testscore form，当老师要提交学生的考试成绩时，在test form中会有一个包含学生姓名的下拉表单，所以老师可以选择哪个学生他想把考试成绩分配给。

写完下面的代码后，我得到了这个错误:

TypeError at /submiit_test/ 
 
coercing to Unicode: need string or buffer, User found 

模型.py

class Student(models.Model): 
     user=models.ForeignKey(User,unique=True) 
     pic=models.ImageField(upload_to="profile_image") 
     first_name=models.CharField(max_length=100) 
     last_name=models.CharField(max_length=100) 
 
class TestScore(models.Model): 
    user=models.ForeignKey(User) 
    studd=models.ForeignKey(Student) 
    year=models.CharField(max_length=20) 
    subject_1=models.CharField(max_length=50, choices=SUBJECT_CHOICES) 
    score_1=models.CharField(max_length=50) 
    subject_2=models.CharField(max_length=50, choices=SUBJECT_CHOICES) 
    score_2=models.CharField(max_length=50) 
    subject_3=models.CharField(max_length=50, choices=SUBJECT_CHOICES) 
    score_3=models.CharField(max_length=50) 
 
    def __unicode__(self): 
        return unicode(self.studd) 
 
 class TestScoreForm(ModelForm): 
      class Meta: 
         model=TestScore 
         fields=('year','studd','subject_1','score_1','subject_2','score_2','subject_3','score_3') 

View .py

def test_submit(request): 
    if request.method=="POST": 
       form=TestScoreForm(request.POST, request.FILES) 
       if form.is_valid(): 
            data=form.cleaned_data 
            newtest=TestScore( 
               user=request.user, 
               studd=data['studd'], 
               year=data['year'], 
               subject_1=data['subject_1'], 
               score_1=data['score_1'], 
               subject_2=data['subject_2'], 
               score_2=data['score_2'], 
               subject_3=data['subject_3'], 
               score_3=data['score_3']) 
           newtest.save() 
           return HttpResponse('thanks') 
        else: 
            return HttpResponse('fill the form correctly') 
     else: 
        return render_to_response('posttest.html',{'TestScoreForm':TestScoreForm,'TestScore':TestScore},context_instance=RequestContext(request)) 

请您参考如下方法:

我已经修好了。这是从

Student

模型。我不得不将其更改为

def __unicode__(self): 
     return '%s' % (self.user)