Fix normalization

src/pretix/helpers/models.py

@@ -20,6 +20,7 @@
 # <https://www.gnu.org/licenses/>.
 #
 import copy
+from decimal import Decimal
 
 from django.core.files import File
 from django.db import models
@@ -57,6 +58,21 @@ def flatten_choices(choices):
             yield value_or_group, label_or_nested
 
 
+def _normalize_decimal(d: Decimal) -> Decimal:
+    """
+    Strips trailing zeros, e.g.
+
+    20.000 → 20
+    20.010 → 20.01
+    20.100 → 20.1
+
+    But unlike of Decimal.normalize(), 20.000 will not become 2e+1
+    """
+    normalized = d.normalize()
+    sign, digit, exponent = normalized.as_tuple()
+    return normalized if exponent <= 0 else normalized.quantize(1)
+
+
 class NormalizedDecimalField(DecimalField):
     """
     Variant of DecimalField that never outputs the trailing zeros, so we always have normalized decimals internally.
@@ -65,5 +81,5 @@ class NormalizedDecimalField(DecimalField):
 
     def from_db_value(self, value, expression, connection):
         if value is not None:
-            value = value.normalize()
+            value = _normalize_decimal(value)
         return value