from django.template import Library, Node, Variable

register = Library()

class LoadFormObjectsNode( Node ):
    def __init__( self, form_objects, var_name ):
        self.var_name = var_name
        form, self.field = form_objects.split('.')
        self.form = Variable(form)

    def render( self, context ):
        form = self.form.resolve( context )
        object_ids = form.data.getlist(self.field)
        objects = form.fields[self.field].queryset
        objects = objects.filter(pk__in=object_ids)
        context[self.var_name] = objects
        return ''


@register.tag
def load_form_objects( parser, token ):
    """Parse template tag: {% load_form_objects form.objects as objects %}"""
    bits = token.contents.split()
    if len( bits ) != 4:
        raise TemplateSyntaxError, "load_form_objects form.objects as objects"
    if bits[2] != 'as':
        raise TemplateSyntaxError, "third argument to the load_form_objects tag must be 'as'"
    return LoadFormObjectsNode( bits[1], bits[3] )