Support fractional VAT rates

Allow fractional tax rates, up to 6 decimal places.

Author: Steve Singer, with some fixes from me

Fixes #164

postgresqleu/invoices/migrations/0021_alter_vatrate_vatpercent.py

@@ -0,0 +1,20 @@
+# Generated by Django 3.2.22 on 2024-09-29 02:12
+
+import django.core.validators
+from django.db import migrations
+import postgresqleu.invoices.models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('invoices', '0020_regtransfer_processor'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='vatrate',
+            name='vatpercent',
+            field=postgresqleu.util.fields.NormalizedDecimalField(decimal_places=6, default=0, max_digits=9, validators=[django.core.validators.MaxValueValidator(100), django.core.validators.MinValueValidator(0)], verbose_name='VAT percentage'),
+        ),
+    ]

postgresqleu/invoices/models.py

@@ -12,7 +12,7 @@
 
 from postgresqleu.util.validators import ListOfEmailAddressValidator
 from postgresqleu.util.checksum import luhn
-from postgresqleu.util.fields import LowercaseEmailField
+from postgresqleu.util.fields import LowercaseEmailField, NormalizedDecimalField
 from postgresqleu.accounting.models import Account, JournalEntry
 
 
@@ -238,10 +238,8 @@ class Meta:
 class VatRate(models.Model):
     name = models.CharField(max_length=100, blank=False, null=False)
     shortname = models.CharField(max_length=16, blank=False, null=False, verbose_name="Short name")
-    vatpercent = models.IntegerField(null=False, default=0, verbose_name="VAT percentage",
-                                     validators=[MaxValueValidator(100), MinValueValidator(0)])
+    vatpercent = NormalizedDecimalField(null=False, default=0, verbose_name="VAT percentage", max_digits=9, decimal_places=6, validators=[MaxValueValidator(100), MinValueValidator(0)])
     vataccount = models.ForeignKey(Account, null=False, blank=False, on_delete=models.CASCADE, verbose_name="VAT account")
-
     _safe_attributes = ('vatpercent', 'shortstr', 'shortname', 'name')
 
     def __str__(self):

postgresqleu/util/fields.py

@@ -1,3 +1,4 @@
+from decimal import Decimal
 from django.db import models
 from django.core.exceptions import ValidationError
 from .forms import ImageBinaryFormField, PdfBinaryFormField
@@ -117,3 +118,11 @@ def to_python(self, value):
 class UserModelChoiceField(ModelChoiceField):
     def label_from_instance(self, obj):
         return "{0} - {1} {2} <{3}>".format(obj.username, obj.first_name, obj.last_name, obj.email)
+
+
+class NormalizedDecimalField(models.DecimalField):
+    def from_db_value(self, value, expression, connection):
+        return value.quantize(Decimal(1)) if value == value.to_integral() else value.normalize()
+
+    def to_python(self, value):
+        return super().to_python(value).quantize(Decimal(1)) if value == value.to_integral() else value.normalize()

template/confreg/admin_backend_form.html

@@ -234,8 +234,8 @@
 
    $('.backend-vat-field').each(function(i, e) {
       $(e).change(function(e) {
-         if ($(this).hasClass('backend-vat-reg-field')) { vatrate = 1.{{conference.vat_registrations.vatpercent|default:0}};}
-         else if ($(this).hasClass('backend-vat-sponsor.field')) { vatrate = 1.{{conference.vat_sponsorship.vatpercent|default:0}};}
+         if ($(this).hasClass('backend-vat-reg-field')) { vatrate = 1 + {{conference.vat_registrations.vatpercent|default:0}}/100;}
+         else if ($(this).hasClass('backend-vat-sponsor-field')) { vatrate = 1 + {{conference.vat_sponsorship.vatpercent|default:0}}/100;}
          else return;
          if (vatrate == 1) return;