Test whether the slug is unique within a given time period.

def validate_unique_slug(self, cleaned_data):
        """
        Test whether the slug is unique within a given time period.
        """
        date_kwargs = {}
        error_msg = _("The slug is not unique")

        # The /year/month/slug/ URL determines when a slug can be unique.
        pubdate = cleaned_data['publication_date'] or now()
        if '{year}' in appsettings.FLUENT_BLOGS_ENTRY_LINK_STYLE:
            date_kwargs['year'] = pubdate.year
            error_msg = _("The slug is not unique within it's publication year.")
        if '{month}' in appsettings.FLUENT_BLOGS_ENTRY_LINK_STYLE:
            date_kwargs['month'] = pubdate.month
            error_msg = _("The slug is not unique within it's publication month.")
        if '{day}' in appsettings.FLUENT_BLOGS_ENTRY_LINK_STYLE:
            date_kwargs['day'] = pubdate.day
            error_msg = _("The slug is not unique within it's publication day.")

        date_range = get_date_range(**date_kwargs)

        # Base filters are configurable for translation support.
        dup_filters = self.get_unique_slug_filters(cleaned_data)
        if date_range:
            dup_filters['publication_date__range'] = date_range

        dup_qs = EntryModel.objects.filter(**dup_filters)

        if self.instance and self.instance.pk:
            dup_qs = dup_qs.exclude(pk=self.instance.pk)

        # Test whether the slug is unique in the current month
        # Note: doesn't take changes to FLUENT_BLOGS_ENTRY_LINK_STYLE into account.
        if dup_qs.exists():
            raise ValidationError(error_msg)