Django：多选表单字段的验证器

I have a multiple choice field in my form where users are given a list of fields, and they can select a maximum of three choices. I've defined a custom validator for restricting users from selecting more than three fields.

我的表单中有一个多选字段，用户可以在其中获得字段列表，并且最多可以选择三个选项。我已经定义了一个自定义验证器来限制用户选择三个以上的字段。

forms.py

class EvangelizedForm(forms.ModelForm):
    area_of_interest = forms.CharField(
        max_length=1230,
        widget=forms.CheckboxSelectMultiple(
            choices=Evangelized.AREA_CHOICES),
        help_text="Areas of interest(Upto 3)")

I have defined a custom form validator named len_area in models.py as follows:

我在models.py中定义了一个名为len_area的自定义表单验证器，如下所示：

def len_area(li):
    if len(li) > 3:
        raise ValidationError("Please select a maximum of three fields only")

models.py

class Evangelized(models.Model):
    AREA_CHOICES = (
        ('Govt', 'Govt'),
        ('Entertainment', 'Entertainment'),
        ('Automobile', 'Automobile'),
        ('Careers', 'Careers'),
        ('Books','Books'),
        ('Family', 'Family'),
        ('Food', 'Food'),
        ('Gaming', 'Gaming'),
        ('Beauty', 'Beauty'),
        ('Sports','Sports'),
        ('Events', 'Events'),
        ('Business', 'Business'),
        ('Travel', 'Travel'),
        ('Health', 'Health'),
        ('Technology','Technology'),
    ) 
    area_of_interest = models.CharField(
        max_length=1280,
        validators=[len_area])

However, the ValidationError message gets thrown at the user at all times, i.e even when the selected fields are three or less than three.

但是，ValidationError消息始终被抛出，即使所选字段为三个或少于三个。

What seems to be wrong with my validator function?

我的验证器功能似乎有什么问题？

2 个解决方案

#1

My guess is that value, returned by CheckboxSelectMultiple's value_from_datadict method, is list [u'abc', u'xyz']. Then it is converted to string [u'abc', u'xyz'] by field's to_python method (actually, it is u"[u'abc', u'xyz']"). After validators are run. Length of this string is more than 3, that's why you got ValidationError.

我的猜测是，CheckboxSelectMultiple的value_from_datadict方法返回的值是list [u'abc'，u'xyz']。然后它通过字段的to_python方法转换为字符串[u'abc'，u'xyz']（实际上，它是你“[u'abc'，u'xyz']”）。验证器运行后。这个字符串的长度超过3，这就是你得到ValidationError的原因。

You should use ManyToManyField.

您应该使用ManyToManyField。

#2

The reason why my validator wasn't working as intended was because the argument passed to the validator, say [u'abc', u'xyz'], was a string and not a list as I earlier thought while defining my validator. As a result, as rightly pointed out by @f43d65, the length of the argument exceeded 3 every single time, and hence the ValidationError was being raised.

我的验证器没有按预期工作的原因是因为传递给验证器的参数，比如[u'abc'，u'xyz']，是一个字符串而不是我之前在定义验证器时所考虑的列表。结果，正如@ f43d65正确指出的那样，参数的长度每次都超过3，因此引发了ValidationError。

I made the following changes in my validator in order for it to work as intended:

我在验证器中进行了以下更改，以使其按预期工作：

def len_area(li):
    if li.count("u'") > 3:
        raise ValidationError("Please select a maximum of three fields only")

#1