formOoject.is_valid()調用如下方法:

return self.is_bound and not self.error

其中is_bound可以認為是否是有傳入(綁定) 
重點是self.error
進入這個方法‘

1     @property
2     def errors(self):
3         "Returns an ErrorDict for the data provided for the form"
4         if self._errors is None:
5             self.full_clean()
6         return
 
 self._errors

從第5行得知,這個方法的核心是full_clean(),查看他的方法:

 1  def full_clean(self):
 2         """
 3         Cleans all of self.data and populates self._errors and
 4         self.cleaned_data.
 5         """
 6         self._errors = ErrorDict()
 7         if not self.is_bound:  # Stop further processing.
 

 8             return
 9         self.cleaned_data = {}
10         # If the form is permitted to be empty, and none of the form data has
11         # changed from the initial data, short circuit any validation.
12         if self.empty_permitted and not self.has_changed():
13             return
14 
15
 
 self._clean_fields()
16 self._clean_form()
17         self._post_clean()

重點在於15,16,17行

首先查看15行的實現:

 1     def _clean_fields(self):
 2         for name, field in self.fields.items():
 3             # value_from_datadict() gets the data from the data dictionaries.
 4             # Each widget type knows how to retrieve its own data, because some
 5             # widgets split data over several HTML fields.
 6             if field.disabled:
 7                 value = self.get_initial_for_field(field, name)
 8             else:
 9                 value = field.widget.value_from_datadict(self.data, self.files, self.add_prefix(name))
10             try:
11                 if isinstance(field, FileField):
12                     initial = self.get_initial_for_field(field, name)
13                     value = field.clean(value, initial)
14                 else:
15                     value = field.clean(value)
16                 self.cleaned_data[name] = value
17                 if hasattr(self, ‘clean_%s‘ % name):
18                     value = getattr(self, ‘clean_%s‘ % name)()
19                     self.cleaned_data[name] = value
20             except ValidationError as e:
21                 self.add_error(name, e)
註意17,18行;這裏提供了一個鉤子.既  clean_字段 ,這裏通過反射的形式進行調用

接下來是16行:

1     def _clean_form(self):
2         try:
3             cleaned_data = self.clean()
4         except ValidationError as e:
5             self.add_error(None, e)
6         else:
7             if cleaned_data is not None:
8                 self.cleaned_data = cleaned_data
這裏,第3行調用了鉤子,我們可以覆寫這個方法

最後是17行:

1     def _post_clean(self):
2         """
3         An internal hook for performing additional cleaning after form cleaning
4         is complete. Used for model validation in model forms.
5         """
6         pass
鉤子

Django --form驗證