I'm using a ModelForm class to generate a bunch of checkboxes for a ManyToManyField but I've run into one problem: while the default behaviour automatically checks the appropriate boxes (when I'm editing an object), I can't figure out how to get that information in my own custom templatetag.

Here's what I've got in my model:

...
from django.forms import CheckboxSelectMultiple, ModelMultipleChoiceField

interests = ModelMultipleChoiceField(widget=CheckboxSelectMultiple(), queryset=Interest.objects.all(), required=False)
...

And here's my templatetag:

@register.filter
def alignboxes(boxes, cls):
    """
        Details on how this works can be found here:
            http://docs.djangoproject.com/en/1.1/howto/custom-template-tags/
    """

    r = ""
    i = 0
    for box in boxes.field.choices.queryset:
        r += "<label for=\"id_%s_%d\" class=\"%s\"><input type=\"checkbox\" name=\"%s\" value=\"%s\" id=\"id_%s_%d\" /> %s</label>\n" % (
            boxes.name,
            i,
            cls,
            boxes.name,
            box.id,
            boxes.name,
            i,
            box.name
        )
        i = i + 1

    return mark_safe(r)

The thing is, I'm only doing this so I can wrap some simpler markup around these boxes, so if someone knows how to make that happen in an easier way, I'm all ears. I'd be happy with knowing a way to access whether or not a box should be checked though.