Implement auto-rounding decimal field

Ref: https://stackoverflow.com/questions/37958130/automatically-round-djangos-decimalfield-according-to-the-max-digits-and-decima

InvenTree/InvenTree/fields.py

@@ -8,6 +8,8 @@ from .validators import allowable_url_schemes
 from django.forms.fields import URLField as FormURLField
 from django.db import models as models
 from django.core import validators
+from django import forms
+from decimal import Decimal
 
 
 class InvenTreeURLFormField(FormURLField):
@@ -25,3 +27,33 @@ class InvenTreeURLField(models.URLField):
         return super().formfield(**{
             'form_class': InvenTreeURLFormField
         })
+
+
+def round_decimal(value, places):
+    """
+    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)
+    return value
+
+
+class RoundingDecimalFormField(forms.DecimalField):
+    def to_python(self, value):
+        value = super(RoundingDecimalFormField, self).to_python(value)
+        return round_decimal(value, self.decimal_places)
+
+
+class RoundingDecimalField(models.DecimalField):
+    def to_python(self, value):
+        value = super(RoundingDecimalField, self).to_python(value)
+        return round_decimal(value, self.decimal_places)
+
+    def formfield(self, **kwargs):
+        defaults = {
+            'form_class': RoundingDecimalFormField
+        }
+        defaults.update(kwargs)
+        return super(RoundingDecimalField, self).formfield(**kwargs)

InvenTree/company/forms.py

@@ -6,6 +6,7 @@ Django Forms for interacting with Company app
 from __future__ import unicode_literals
 
 from InvenTree.forms import HelperForm
+from InvenTree.fields import RoundingDecimalFormField
 
 from .models import Company
 from .models import SupplierPart
@@ -64,6 +65,10 @@ class EditSupplierPartForm(HelperForm):
 class EditPriceBreakForm(HelperForm):
     """ Form for creating / editing a supplier price break """
 
+    quantity = RoundingDecimalFormField(max_digits=10, decimal_places=5)
+
+    cost = RoundingDecimalFormField(max_digits=10, decimal_places=5)
+
     class Meta:
         model = SupplierPriceBreak
         fields = [

InvenTree/company/migrations/0011_auto_20200318_1114.py

@@ -0,0 +1,20 @@
+# Generated by Django 2.2.9 on 2020-03-18 11:14
+
+import InvenTree.fields
+import django.core.validators
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('company', '0010_auto_20200201_1231'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='supplierpricebreak',
+            name='cost',
+            field=InvenTree.fields.RoundingDecimalField(decimal_places=5, max_digits=10, validators=[django.core.validators.MinValueValidator(0)]),
+        ),
+    ]

InvenTree/company/migrations/0012_auto_20200318_1114.py

@@ -0,0 +1,20 @@
+# Generated by Django 2.2.9 on 2020-03-18 11:14
+
+import InvenTree.fields
+import django.core.validators
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('company', '0011_auto_20200318_1114'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='supplierpricebreak',
+            name='quantity',
+            field=InvenTree.fields.RoundingDecimalField(decimal_places=5, default=1, max_digits=15, validators=[django.core.validators.MinValueValidator(1)]),
+        ),
+    ]

InvenTree/company/models.py

@@ -21,7 +21,7 @@ from django.conf import settings
 
 from markdownx.models import MarkdownxField
 
-from InvenTree.fields import InvenTreeURLField
+from InvenTree.fields import InvenTreeURLField, RoundingDecimalField
 from InvenTree.status_codes import OrderStatus
 from common.models import Currency
 
@@ -381,9 +381,9 @@ class SupplierPriceBreak(models.Model):
 
     part = models.ForeignKey(SupplierPart, on_delete=models.CASCADE, related_name='pricebreaks')
 
-    quantity = models.DecimalField(max_digits=15, decimal_places=5, default=1, validators=[MinValueValidator(1)])
+    quantity = RoundingDecimalField(max_digits=15, decimal_places=5, default=1, validators=[MinValueValidator(1)])
 
-    cost = models.DecimalField(max_digits=10, decimal_places=5, validators=[MinValueValidator(0)])
+    cost = RoundingDecimalField(max_digits=10, decimal_places=5, validators=[MinValueValidator(0)])
 
     currency = models.ForeignKey(Currency, blank=True, null=True, on_delete=models.SET_NULL)