In Django form, custom SelectField and SelectMultipleField

Question

I am using Django everyday now for three month and it is really great. Fast web application development.

I have still one thing that I cannot do exactly how I want to. It is the SelectField and SelectMultiple Field.

I want to be able to put some args to an option of a Select.

I finally success with the optgroup :

class EquipmentField(forms.ModelChoiceField):
    def __init__(self, queryset, **kwargs):
        super(forms.ModelChoiceField, self).__init__(**kwargs)
        self.queryset = queryset
        self.to_field_name=None

        group = None
        list = []
        self.choices = []

        for equipment in queryset:
            if not group:
                group = equipment.type

            if group != equipment.type:
                self.choices.append((group.name, list))
                group = equipment.type
                list = []
            else:
                list.append((equipment.id, equipment.name))

But for another ModelForm, I have to change the background color of every option, using the color property of the model.

Do you know how I can do that ?

Thank you.

Answer 1

What you need to do, is to change the output which is controlled by the widget. Default is the select widget, so you can subclass it. It looks like this:

class Select(Widget):
    def __init__(self, attrs=None, choices=()):
        super(Select, self).__init__(attrs)
        # choices can be any iterable, but we may need to render this widget
        # multiple times. Thus, collapse it into a list so it can be consumed
        # more than once.
        self.choices = list(choices)

    def render(self, name, value, attrs=None, choices=()):
        if value is None: value = ''
        final_attrs = self.build_attrs(attrs, name=name)
        output = [u'<select%s>' % flatatt(final_attrs)]
        options = self.render_options(choices, [value])
        if options:
            output.append(options)
        output.append('</select>')
        return mark_safe(u'\n'.join(output))

    def render_options(self, choices, selected_choices):
        def render_option(option_value, option_label):
            option_value = force_unicode(option_value)
            selected_html = (option_value in selected_choices) and u' selected="selected"' or ''
            return u'<option value="%s"%s>%s</option>' % (
                escape(option_value), selected_html,
                conditional_escape(force_unicode(option_label)))
        # Normalize to strings.
        selected_choices = set([force_unicode(v) for v in selected_choices])
        output = []
        for option_value, option_label in chain(self.choices, choices):
            if isinstance(option_label, (list, tuple)):
                output.append(u'<optgroup label="%s">' % escape(force_unicode(option_value)))
                for option in option_label:
                    output.append(render_option(*option))
                output.append(u'</optgroup>')
            else:
                output.append(render_option(option_value, option_label))
        return u'\n'.join(output)

It's a lot of code. But what you need to do, is to make your own widget with an altered render method. It's the render method that determines the html that is created. In this case, it's the render_options method you need to change. Here you could include some check to determine when to add a class, which you could style.

Another thing, in your code above it doesn't look like you append the last group choices. Also you might want to add an order_by() to the queryset, as you need it to be ordered by the type. You could do that in the init method, so you don't have to do it all over when you use the form field.

Answer 2

You should not mess with form fields for adding some custom attributes to the rendered html tag. But you should subclass and add a these to the Widget.

From the docs: customizing-widget-instances

You can submit attrs dictionary to the form Widgets, that render as attributes on the output form widgets.

class CommentForm(forms.Form):
    name = forms.CharField(
                widget=forms.TextInput(attrs={'class':'special'}))
    url = forms.URLField()
    comment = forms.CharField(
               widget=forms.TextInput(attrs={'size':'40'}))
Django will then include the extra attributes in the rendered output:

>>> f = CommentForm(auto_id=False)
>>> f.as_table()
<tr><th>Name:</th><td><input type="text" name="name" class="special"/></td></tr>
<tr><th>Url:</th><td><input type="text" name="url"/></td></tr>
<tr><th>Comment:</th><td><input type="text" name="comment" size="40"/></td></tr>