Floating point API bug (#3877)

* Add unit tests for internalpricebreak

- Exposes an existing bug

* Ensure that rounding-decimal and prices are rounded correctly

- Force remove trailing digits / reduce precision

InvenTree/InvenTree/fields.py

@@ -91,6 +91,18 @@ class InvenTreeModelMoneyField(ModelMoneyField):
         kwargs['form_class'] = InvenTreeMoneyField
         return super().formfield(**kwargs)
 
+    def to_python(self, value):
+        """Convert value to python type."""
+        value = super().to_python(value)
+        return round_decimal(value, self.decimal_places)
+
+    def prepare_value(self, value):
+        """Override the 'prepare_value' method, to remove trailing zeros when displaying.
+
+        Why? It looks nice!
+        """
+        return round_decimal(value, self.decimal_places, normalize=True)
+
 
 class InvenTreeMoneyField(MoneyField):
     """Custom MoneyField for clean migrations while using dynamic currency settings."""
@@ -126,11 +138,16 @@ class DatePickerFormField(forms.DateField):
         )
 
 
-def round_decimal(value, places):
+def round_decimal(value, places, normalize=False):
     """Round value to the specified number of places."""
-    if value is not None:
-        # see https://docs.python.org/2/library/decimal.html#decimal.Decimal.quantize for options
-        return value.quantize(Decimal(10) ** -places)
+
+    if type(value) in [Decimal, float]:
+        value = round(value, places)
+
+        if normalize:
+            # Remove any trailing zeroes
+            value = InvenTree.helpers.normalize(value)
+
     return value
 
 
@@ -140,18 +157,14 @@ class RoundingDecimalFormField(forms.DecimalField):
     def to_python(self, value):
         """Convert value to python type."""
         value = super().to_python(value)
-        value = round_decimal(value, self.decimal_places)
-        return value
+        return round_decimal(value, self.decimal_places)
 
     def prepare_value(self, value):
         """Override the 'prepare_value' method, to remove trailing zeros when displaying.
 
         Why? It looks nice!
         """
-        if type(value) == Decimal:
-            return InvenTree.helpers.normalize(value)
-        else:
-            return value
+        return round_decimal(value, self.decimal_places, normalize=True)
 
 
 class RoundingDecimalField(models.DecimalField):

InvenTree/InvenTree/serializers.py

@@ -34,13 +34,14 @@ class InvenTreeMoneySerializer(MoneyField):
     def __init__(self, *args, **kwargs):
         """Overrite default values."""
         kwargs["max_digits"] = kwargs.get("max_digits", 19)
-        kwargs["decimal_places"] = kwargs.get("decimal_places", 4)
+        self.decimal_places = kwargs["decimal_places"] = kwargs.get("decimal_places", 4)
         kwargs["required"] = kwargs.get("required", False)
 
         super().__init__(*args, **kwargs)
 
     def get_value(self, data):
         """Test that the returned amount is a valid Decimal."""
+
         amount = super(DecimalField, self).get_value(data)
 
         # Convert an empty string to None
@@ -49,7 +50,9 @@ class InvenTreeMoneySerializer(MoneyField):
 
         try:
             if amount is not None and amount is not empty:
+                # Convert to a Decimal instance, and round to maximum allowed decimal places
                 amount = Decimal(amount)
+                amount = round(amount, self.decimal_places)
         except Exception:
             raise ValidationError({
                 self.field_name: [_("Must be a valid number")],

InvenTree/part/test_api.py

@@ -1,5 +1,6 @@
 """Unit tests for the various part API endpoints"""
 
+from decimal import Decimal
 from random import randint
 
 from django.urls import reverse
@@ -2430,3 +2431,65 @@ class PartAttachmentTest(InvenTreeAPITestCase):
         self.assertEqual(data['part'], 1)
         self.assertEqual(data['link'], link)
         self.assertEqual(data['comment'], 'Hello world')
+
+
+class PartInternalPriceBreakTest(InvenTreeAPITestCase):
+    """Unit tests for the PartInternalPrice API endpoints"""
+
+    fixtures = [
+        'category',
+        'part',
+        'params',
+        'location',
+        'bom',
+        'company',
+        'test_templates',
+        'manufacturer_part',
+        'supplier_part',
+        'order',
+        'stock',
+    ]
+
+    roles = [
+        'part.change',
+        'part.add',
+        'part.delete',
+        'part_category.change',
+        'part_category.add',
+        'part_category.delete',
+    ]
+
+    def test_create_price_breaks(self):
+        """Test we can create price breaks at various quantities"""
+
+        url = reverse('api-part-internal-price-list')
+
+        breaks = [
+            (1.0, 101),
+            (1.1, 92.555555555),
+            (1.5, 90.999999999),
+            (1.756, 89),
+            (2, 86),
+            (25, 80)
+        ]
+
+        for q, p in breaks:
+            data = self.post(
+                url,
+                {
+                    'part': 1,
+                    'quantity': q,
+                    'price': p,
+                },
+                expected_code=201
+            ).data
+
+            self.assertEqual(data['part'], 1)
+            self.assertEqual(
+                round(Decimal(data['quantity']), 4),
+                round(Decimal(q), 4)
+            )
+            self.assertEqual(
+                round(Decimal(data['price']), 4),
+                round(Decimal(p), 4)
+            )