python---django中form组件（数据添加前使用自定义方法进行验证，以及源码分析）

from app02.models import Userfrom django.core.exceptions import ValidationError

class AjaxForm(forms.Form):
    user = fields.CharField(
        required=True,
        min_length=3,
        max_length=7,
    )
    email = fields.EmailField(
        required=True,
    )

    #自定义方法 clean_字段名
    #必须返回值self.cleaned_data[‘user‘]
    #如果出错抛出raise ValidationError("error...")
　　#会在基础验证成功后，使用自定义方法进行验证
    def clean_user(self):
        v = self.cleaned_data[‘user‘]
        if User.objects.filter(username=v).count():
            #重复了
            raise ValidationError("用户名已存在")
        return v

    def clean_email(self):

        return self.cleaned_data[‘email‘]

def ajax(req):
    if req.method == "GET":
        obj = AjaxForm()
        return render(req,"ajax.html",{"obj":obj})
    else:
        ret={}
        obj = AjaxForm(req.POST)
        if obj.is_valid():  #在使用is_valid之后才会将数据进行验证
            ret[‘status‘]="OK"
            return HttpResponse(json.dumps(ret))
        else:
            print(obj.errors)
            ret[‘message‘]=obj.errors
            return HttpResponse(json.dumps(ret))

class BaseForm:
       def is_valid(self):
        """
        Returns True if the form has no errors. Otherwise, False. If errors are
        being ignored, returns False.
        """若是表单数据正确，则返回true
        return self.is_bound and not self.errors #是属性方法，进行字段验证

self.is_bound = data is not None or files is not None #data传入表单数据不为空，所以is_bound=true

    @property
    def errors(self):
        "Returns an ErrorDict for the data provided for the form"#返回错误信息为表单数据
        if self._errors is None:  #初始self._errors是null    
            self.full_clean()　　　#进入该方法
        return self._errors

    def full_clean(self):
        """
        Cleans all of self.data and populates self._errors and
        self.cleaned_data.
        """
        self._errors = ErrorDict()   #初始化错误字典
        if not self.is_bound:  # Stop further processing.
            return
        self.cleaned_data = {}　　　　#初始化正确数据
        # If the form is permitted to be empty, and none of the form data has
        # changed from the initial data, short circuit any validation.
        if self.empty_permitted and not self.has_changed():  #如果允许为空，并且数据为从初始状态进行改变，则直接返回
            return
　　　　 #下面是开始验证的方法
        self._clean_fields()
        self._clean_form()
        self._post_clean()

    def _clean_fields(self):
　　　　  #循环字段，在form组件中设置的字段，该字段来自于DeclarativeFieldsMetaclass的__new__
        for name, field in self.fields.items():
            # value_from_datadict() gets the data from the data dictionaries.
            # Each widget type knows how to retrieve its own data, because some
            # widgets split data over several HTML fields.
            if field.disabled:
                value = self.get_initial_for_field(field, name)
            else:
                value = field.widget.value_from_datadict(self.data, self.files, self.add_prefix(name))
            try:
                if isinstance(field, FileField):
                    initial = self.get_initial_for_field(field, name)
                    value = field.clean(value, initial)
                else:
                    value = field.clean(value)
                self.cleaned_data[name] = value
　　　　　　　　　#上面尝试进行正则验证，验证成功后，开始下面逻辑
　　　　　　　　  #会调用 clean_%s方法name是字段名，这就是我们的自定义方法，我们可以在已经满足正则验证后的数据
　　　　　　　　  #上再次进行自定义函数的验证，比如验证数据库数据的唯一性处理
                if hasattr(self, ‘clean_%s‘ % name):
                    value = getattr(self, ‘clean_%s‘ % name)()
                    self.cleaned_data[name] = value　　#注意：最终的值取决于自定义方法：前提是已经存在该方法
            except ValidationError as e:     #在自定义方法上，如果验证出错，我们需要抛出该错误让该方法进行捕获
                self.add_error(name, e)