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.

Pimpernel

Answer 1

render_option has been removed from Django 1.11 onwards. This is what I did to achieve this. A little bit of digging and this seems straightforward and neat. Works with Django 2.0+

class CustomSelect(forms.Select):
    def __init__(self, attrs=None, choices=()):
        self.custom_attrs = {}
        super().__init__(attrs, choices)

    def create_option(self, name, value, label, selected, index, subindex=None, attrs=None):
        index = str(index) if subindex is None else "%s_%s" % (index, subindex)
        if attrs is None:
            attrs = {}
        option_attrs = self.build_attrs(self.attrs, attrs) if self.option_inherits_attrs else {}
        if selected:
            option_attrs.update(self.checked_attribute)
        if 'id' in option_attrs:
            option_attrs['id'] = self.id_for_label(option_attrs['id'], index)

        # setting the attributes here for the option
        if len(self.custom_attrs) > 0:
            if value in self.custom_attrs:
                custom_attr = self.custom_attrs[value]
                for k, v in custom_attr.items():
                    option_attrs.update({k: v})

        return {
            'name': name,
            'value': value,
            'label': label,
            'selected': selected,
            'index': index,
            'attrs': option_attrs,
            'type': self.input_type,
            'template_name': self.option_template_name,
        }


class MyModelChoiceField(ModelChoiceField):

    # custom method to label the option field
    def label_from_instance(self, obj):
        # since the object is accessible here you can set the extra attributes
        if hasattr(obj, 'type'):
            self.widget.custom_attrs.update({obj.pk: {'type': obj.type}})
        return obj.get_display_name()

The form:

class BookingForm(forms.ModelForm):

    customer = MyModelChoiceField(required=True,
                                  queryset=Customer.objects.filter(is_active=True).order_by('name'),
                                  widget=CustomSelect(attrs={'class': 'chosen-select'}))

The output which I needed is as:

  <select name="customer" class="chosen-select" required="" id="id_customer">
      <option value="" selected="">---------</option>
      <option value="242" type="CNT">AEC Transcolutions Private Limited</option>
      <option value="243" type="CNT">BBC FREIGHT CARRIER</option>
      <option value="244" type="CNT">Blue Dart Express Limited</option>

Plauen

Great way to override the options. Do you know a way to override SELECT's 'name' and 'id' ? Can't find this anywhere – Sensorimotor

You could shorten the code by calling super().create_option(). – Kink

Answer 2

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.

Chrome

Ok, so I should create a full SelectWidget. I will try it, thank you. – Pimpernel

Answer 3

I run into this question many times when searching by

'how to customize/populate Django SelectField options'

The answer provided by Dimitris Kougioumtzis is quite easy

Hope it could help somebody like me.

# forms.py
from django.forms import ModelForm, ChoiceField
from .models import MyChoices

class ProjectForm(ModelForm):
    choice = ChoiceField(choices=[
        (choice.pk, choice) for choice in MyChoices.objects.all()])

# admin.py
class ProjectAdmin(BaseAdmin):
    form = ProjectForm
    ....

Orpine

Any suggestion on how to overide 'id' and 'name' of the Select element? – Sensorimotor

Answer 4

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>

Backstop

This is for common field. And I already do that, but how do you do that for option of a SelectWidget ? – Pimpernel

This doesn't explain how to add attrs to the <option> elements in a <select>. – Kink

Answer 5

http://code.djangoproject.com/browser/django/trunk/django/newforms/widgets.py?rev=7083

As seen under the class Select(Widget):, there is no way to add the style attribute to an option tag. To this, you will have to subclass this widget and add such functionality.

The class Select(Widget): definition only adds style attribute to the main select tag.

Iconography