Django CheckboxSelectMultiple override 'choices' from ModelForm - django

Question

I would like to be able to extract different information in my django form:
That's my form:
<form action="" method="post">{% csrf_token %}
{{ form.as_p }}
<input type="submit" value="Submit" />
</form>
class InstanceForm(ModelForm):
class Meta:
model = models.BaseAsset
widgets = {
'labels': LabelIconCheckboxSelectMultiple()
}
The model:
class AssetClass(models.Model):
default_labels = models.ManyToManyField(Label, null=True, blank=True)
pass
the M2M reference field
class Label(models.Model):
explanation = models.CharField(null=True, max_length=63)
svgpreview = models.CharField(null=True, max_length=31)
def __unicode__(self):
return unicode(self.explanation)
pass
Now, the HTML code generated by the {{ form.as_p }} is as follows:
<li><label for="id_labels_0"><input type="checkbox" name="labels" value="1" id="id_labels_0" /> Consult owner before using</label></li>
<li><label for="id_labels_1"><input type="checkbox" name="labels" value="2" id="id_labels_1" /> This item is broken</label></li>
Which means it's clearly using the __unicode__ rendering of the model 'Label'. How can I change that behavior in the Select widget, so that it would use a different function to populate it's choices? I'm trying to get it, in the reasonably portable way, to print '<img src="{{label.svgpreview}}" alt="{{label.explanation}}"...>' next to the checkbox?

Answer 1

You will override forms.widgets.CheckboxSelectMultiple class:
This is CheckboxSelectMultiple class and its render function:
class CheckboxSelectMultiple(SelectMultiple):
def render(self, name, value, attrs=None, choices=()):
if value is None: value = []
has_id = attrs and 'id' in attrs
final_attrs = self.build_attrs(attrs, name=name)
output = [u'<ul>']
# Normalize to strings
str_values = set([force_unicode(v) for v in value])
for i, (option_value, option_label) in enumerate(chain(self.choices, choices)):
# If an ID attribute was given, add a numeric index as a suffix,
# so that the checkboxes don't all have the same ID attribute.
if has_id:
final_attrs = dict(final_attrs, id='%s_%s' % (attrs['id'], i))
label_for = u' for="%s"' % final_attrs['id']
else:
label_for = ''
cb = CheckboxInput(final_attrs, check_test=lambda value: value in str_values)
option_value = force_unicode(option_value)
rendered_cb = cb.render(name, option_value)
option_label = conditional_escape(force_unicode(option_label))
output.append(u'<li><label%s>%s %s</label></li>' % (label_for, rendered_cb, option_label))
output.append(u'</ul>')
return mark_safe(u'\n'.join(output))
So what you will do :
class MyCheckboxSelectMultiple(CheckboxSelectMultiple):
def render(self, name, value, attrs=None, choices=()):
#put your code to have custom checkbox control with icon
#...
output.append(u'<li><label%s>%s %s</label></li>' % (label_for, rendered_cb, option_label)) # especially you will be working on this line
#...
Then where you are using widgets=CheckboxSelectMultiple() it will become widgets=MyCheckboxSelectMultiple()

Answer 2

Reading django.forms.models.ModelChoiceField gives a hint:
# this method will be used to create object labels by the QuerySetIterator.
# Override it to customize the label.
def label_from_instance(self, obj):
"""
This method is used to convert objects into strings; it's used to
generate the labels for the choices presented by this object. Subclasses
can override this method to customize the display of the choices.
"""
return smart_unicode(obj)
ok, but how do I override it per-instance of ModelForm - this gets overridden in few places throughout django.forms
Considering the following code:
class InstanceForm(ModelForm):
class Meta:
model = models.BaseAsset
widgets = {
'labels': forms.CheckboxSelectMultiple()
}
def __init__(self, *args, **kwargs):
def new_label_from_instance(self, obj):
return obj.svgpreview
super(InstanceForm, self).__init__(*args, **kwargs)
funcType = type(self.fields['labels'].label_from_instance)
self.fields['labels'].label_from_instance = funcType(new_label_from_instance, self.fields['labels'], forms.models.ModelMultipleChoiceField)
This is somewhat creepy - basically, it's a more bizzare implementation of this:
Override a method at instance level
Please read the comments in the referenced thread to understand why this might be a bad idea in general..

Answer 3

You don't have to do the "creepy" instance-level override to take proper advantage of the documented django.forms.models.ModelChoiceField.label_from_instance() method.
Building on the AssetClass and Label objects in the original post:
class AssetSvgMultiField(forms.ModelMultipleChoiceField):
"""
Custom ModelMultipleChoiceField that labels instances with their svgpreview.
"""
def label_from_instance(self, obj):
return obj.svgpreview
class InstanceForm(forms.ModelForm):
default_labels = AssetSvgMultiField(queryset=Label.objects.all())
class Meta:
model = models.AssetClass
widgets = {
'default_labels': forms.CheckboxSelectMultiple()
}

Answer 4

This is explained in the Django documentation here:
https://docs.djangoproject.com/en/1.9/ref/forms/fields/#django.forms.ModelChoiceField.to_field_name
You can see the ModelChoiceField class calling the method on the field here:
https://github.com/django/django/blob/1155843a41af589a856efe8e671a796866430049/django/forms/models.py#L1174
If you're not overriding choices explicitly, then your code might look like this:
class RectificationAssetMultiField(forms.ModelMultipleChoiceField):
def label_from_instance(self, obj):
return '[{0.pk}] {0.label} ({0.location})'.format(obj)
class RectificationForm(forms.ModelForm):
items = RectificationAssetMultiField(
required=False,
queryset=InspectionItem.objects.all(),
widget=forms.CheckboxSelectMultiple,
label="Non-compliant Assets"
)
class Meta:
model = Rectification
fields = ('ref', 'items', 'status')
Be careful that this will only work if you're not setting choices directly (see _get_choices in the above URL).
If instead you wanted to override choices (for a more efficient result than a queryset, or something better expressed as a ValuesList) then you would have something like this:
class RectificationAssetMultiField(forms.ModelMultipleChoiceField):
def label_from_instance(self, obj):
return '[{0.pk}] {0.label} ({0.location})'.format(obj)
class RectificationForm(forms.ModelForm):
items = RectificationAssetMultiField(
required=False,
queryset=InspectionItem.objects.none(),
widget=forms.CheckboxSelectMultiple,
label="Non-compliant Assets"
)
def __init__(self, *args, **kwargs):
super(RectificationForm, self).__init__(*args, **kwargs)
self.fields['items'].choices = (InspectionItem.objects
.active()
.noncompliant()
.filter(property_id=self.instance.property_id)
.values_list('pk', 'label') # pass a key value pair
)
class Meta:
model = Rectification
fields = ('ref', 'items', 'status')

Answer 5

Don't use {{ form.as_p }} if you don't like that rendering.
Loop over the form instead:
<form action="/contact/" method="post">
{% for field in form %}
<div class="fieldWrapper">
{{ field.errors }}
{{ field.label_tag }}: {{ field }}
</div>
{% endfor %}
<p><input type="submit" value="Send message" /></p>
</form>
You are then free to use whatever HTML you want.
From: https://docs.djangoproject.com/en/dev/topics/forms/#looping-over-the-form-s-fields