Django错误：ValueError

Question

我有两个模型，即时通讯做一个自定义表单，以便我可以查看和保存表单从我的HTML到数据库。但是当我尝试保存时，我得到这个错误。

回溯

Environment: 


Request Method: POST 
Request URL: http://127.0.0.1:8008/ 

Django Version: 1.4 
Python Version: 2.7.3 
Installed Applications: 
('django.contrib.auth', 
'django.contrib.contenttypes', 
'django.contrib.sessions', 
'django.contrib.sites', 
'django.contrib.messages', 
'django.contrib.staticfiles', 
'SecondBlog.blog', 
'django.contrib.admin', 
'django.contrib.admindocs') 
Installed Middleware: 
('django.middleware.common.CommonMiddleware', 
'django.contrib.sessions.middleware.SessionMiddleware', 
'django.middleware.csrf.CsrfViewMiddleware', 
'django.contrib.auth.middleware.AuthenticationMiddleware', 
'django.contrib.messages.middleware.MessageMiddleware') 


Traceback: 
File "c:\Python27\lib\site-packages\django\core\handlers\base.py" in get_response 
    111.       response = callback(request, *callback_args,  **callback_kwargs) 
File "f:\apt3\SecondBlog\SecondBlog\blog\views.py" in home 
    10.   if form.is_valid(): 
File "c:\Python27\lib\site-packages\django\forms\forms.py" in is_valid 
    124.   return self.is_bound and not bool(self.errors) 
File "c:\Python27\lib\site-packages\django\forms\forms.py" in _get_errors 
    115.    self.full_clean() 
File "c:\Python27\lib\site-packages\django\forms\forms.py" in full_clean 
    272.   self._post_clean() 
File "c:\Python27\lib\site-packages\django\forms\models.py" in _post_clean 
    309.   self.instance = construct_instance(self, self.instance, opts.fields,  opts.exclude) 
File "c:\Python27\lib\site-packages\django\forms\models.py" in construct_instance 
    51.    f.save_form_data(instance, cleaned_data[f.name]) 
File "c:\Python27\lib\site-packages\django\db\models\fields\__init__.py" in save_form_data 
    454.   setattr(instance, self.name, data) 
File "c:\Python27\lib\site-packages\django\db\models\fields\related.py" in __set__ 
    366.         self.field.name,  self.field.rel.to._meta.object_name)) 

Exception Type: ValueError at/
Exception Value: Cannot assign "u'Sasa'": "Book.author" must be a "Author" instance. 

models.py

class Author(models.Model): 
    name = models.CharField(max_length = 30) 


    class Book(models.Model): 
    author = models.ForeignKey(Author) 
    title = models.CharField(max_length = 100) 

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

forms.py

class CustomForm(ModelForm): 
    author = forms.CharField() 
    def save(self, commit=True): 
     author = Author.objects.get_or_create(name=self.cleaned_data['author']) 

     instance = super(CustomForm, self).save(commit=commit) 
     instance.author = author 
     if commit: 
      instance.save() 
     return instance 

    class Meta: 
     model = Book 
     fields = ('author','title',) 

views.py

def home(request): 
    if request.method == 'POST': 
     form = CustomForm(request.POST) 
     if form.is_valid(): 

      print "all validated" 
      form.save() 
      return HttpResponseRedirect('index.html') 
     else: 
      print "failed" 
    else: 
     form = CustomForm() 

    variables = RequestContext(request, {'form' : form}) 
    return render_to_response('index.html', variables) 

非常感谢。

Answer 1

我尝试你的代码并做一些测试，不管我做什么我总是会得到那个错误。因为在作者创建之前，该书首先执行导致实例错误。

我修改了您的代码。我删除您的保存方法，并将其更改为现在正在工作的清理方法。

class CustomForm(forms.ModelForm): 
    author = forms.CharField() 

    def clean(self): 
     cleaned_data = super(CustomForm, self).clean() 
     author = cleaned_data.get("author") 

     if not author: 
      raise forms.ValidationError("Please enter an author") 

     data = Author.objects.create(name=author) 

     cleaned_data['author'] = data 

     return cleaned_data 

    class Meta: 
     model = Book 
     fields = ('author','title',) 

Answer 2

的问题是，它甚至没有让你的代码，将笔者的实例，因为超类的保存方法有其设置使用文本字段，这是在错误发生。

你可以尝试或者使用pop调用超，或与作者实例替换该值之前删除从cleaned_data的author值。

编辑例如

def save(self, commit=True): 
    author = Author.objects.get_or_create(name=self.cleaned_data.pop('author')) 

    instance = super(CustomForm, self).save(commit=commit) 

Answer 3

的问题是不是与节约，但表单的验证。基本上，您可以为Book创建一个自定义版本的模型表单，其中有两个字段author和title。默认情况下，author字段将显示为作者类型的参考浏览窗口小部件。

但是，您对author = forms.CharField()所做的操作是告诉窗体显示简单的文本输入字段，而不是作者参考选择器。当它试图验证这个..好吧，它不能。

你需要做的是过程验证之前author值，你可以在clean()功能，您可以添加到您的CustomForm

def clean(self): 
    self.cleaned_data['author'] = Author.objects.get_or_create(name=self.cleaned_data['author']) 
    return self.cleaned_data 

一个非常类似的问题，这样做是how to change form field in method is_valid()