Automatic ordering implementation in Django Models

gistfile1.py

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#                                                 #
#   Default concrete implementations are below.   #
#                                                 #
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class FormEntry(AbstractFormEntry):
    form = models.ForeignKey("Form", related_name="entries")


class FieldEntry(AbstractFieldEntry):
    entry = models.ForeignKey("FormEntry", related_name="fields")


class Form(AbstractForm):
    pass


class Field(AbstractField):
    """
    Implements automated field ordering.
    """

    form = models.ForeignKey("Form", related_name="fields")
    order = models.IntegerField(_("Order"), null=True, blank=True)

    class Meta(AbstractField.Meta):
        ordering = ("order",)

    def save(self, *args, **kwargs):
        if self.order is None:
            self.order = self.form.fields.count()
        super(Field, self).save(*args, **kwargs)

    def delete(self, *args, **kwargs):
        fields_after = self.form.fields.filter(order__gte=self.order)
        fields_after.update(order=models.F("order") - 1)
        super(Field, self).delete(*args, **kwargs)