Limit characters user can enter in input in django view OR html?

Question

I had various occasions where I wanted to but couldn’t limit characters user types in html input. For example what would I do if I would only want numbers and letters? No other like £-“<#>{[. And what would I do if I would want them to only enter uppercase letters? Thanks for help:)

Answer 1

There's a couple of ways you can do this, through Django Form validation, HTML attributes or Javascript.

Django Validation + HTML attributes

class TheForm(forms.ModelForm):
    class Meta:
        model = ModuleChoice
        fields = (
            'text',
            )

    def __init__(self,  *args, **kwargs):
        super(TheForm, self).__init__(*args, **kwargs)

        # HTML attributes:
            # Max Length, user physically couldn't type more than 35
            # some fields also can have the `pattern` attribute which allows you to have REGEX
        self.fields['text'].widget.attrs={'class': 'form-control', 'maxlength': '35'}


    def is_valid(self):
        valid = super(TheForm, self).is_valid()
        if not self.cleaned_data.get('text'):
            self.add_error('text', 'text needs a Value')
            valid = False

        invalidChars = [ '£', '-', '“', '<', '#', '>', '{', '[' ]
        if any([c in self.cleaned_data.get('text') for c in invalidChars]):
            # error ( {field}, {msg} )
            self.add_error('text', 'These £-“<#>{[ characters are Illegal.')
            valid = False

        if self.cleaned_data.get('text').islower():
            self.add_error('text', 'All Letters Must be all Upper Case.')
            valid = False

        # you could also do Regex:
        import re
        if re.findall('^Nealium.*Uncool$', self.cleaned_data.get('text')):
            self.add_error('text', 'You cannot say Nealium is Uncool.')
            valid = False

        # the sky is the limit..
        if The.objects.filter(text=self.cleaned_data.get('text')).count():
            self.add_error('text', 'Duplicate Text.')
            valid = False

        return valid

you would then put, below, in your template and if you re-render the page with the invalid form it'll show them.

{% if form.errors %}{{form.errors}}{% endif %}

Or you can use, below, so access your errors in the template

print(form.errors)
print(form.errors.as_data())

Doing it through Javascript is very Similar to the is_valid() in Django Forms, you'd just override the default form.save event and add a few if statements above submitting it

---

Edit

Yes, you could do it in the View- Specifically in the POST:

def theview(request):
    if request.method == 'POST'
        valid = True
        text = request.POST.get('text')

        invalidChars = [ '£', '-', '“', '<', '#', '>', '{', '[' ]
        if any([c in text for c in invalidChars]):
            msg = 'These £-“<#>{[ characters are Illegal.'
            valid = False

        # other validation

        if valid:
            The.object.create(text=text)
            render(request, 'success.html')
        # not valid

Or you could do it in the Template if you're manually rendering the Form fields

<form method="post">
    <input id="id_text" name="text" maxlength="35"/>
    <submit>Submit</submit>
</form>

---

but if you are rendering your forms in the Template like:

<form method="post">
    {% csrf_token %}
    {{ form }}
    <input type="submit" value="Submit">
</form>

or:

<form method="post">
    {% csrf_token %}
    {{ form.text }}
    <input type="submit" value="Submit">
</form>

and your View looks like:

def theview(request):
    form = TheForm()

    if request.method == 'POST'
        form = TheForm(request.POST)
        if form.is_valid():
            form.save()

            render(request, 'success.html')
      
    data = {
        'form': form,
    }
    return render(request, 'form.html', data)

You might as well do it through the Form object (which was the 1st example)