Include stock item purchase price in pricing cache (#4292)

* Add setting to control pricing calculation from stock items

* Bug fix for displaying a "null" setting

* Add new fields to PartPricing model

* Add code for calculation of min/max stock item costs

* Update pricing display to use stock item pricing

* Add unit testing for new pricing features

* Automatically update pricing when stock item is created or edited

* Increment API version

* Improvements for price rendering

* Update based on feedback:

- Roll stock item pricing into purchase pricing
- Simplify models
- Update unit tests

InvenTree/part/test_pricing.py

@@ -10,6 +10,7 @@ import common.settings
 import company.models
 import order.models
 import part.models
+import stock.models
 from InvenTree.helpers import InvenTreeTestCase
 from InvenTree.status_codes import PurchaseOrderStatus
 
@@ -234,6 +235,54 @@ class PartPricingTests(InvenTreeTestCase):
             self.assertEqual(pricing.internal_cost_max, Money(10, currency))
             self.assertEqual(pricing.overall_max, Money(10, currency))
 
+    def test_stock_item_pricing(self):
+        """Test for stock item pricing data"""
+
+        # Create a part
+        p = part.models.Part.objects.create(
+            name='Test part for pricing',
+            description='hello world',
+        )
+
+        # Create some stock items
+        prices = [
+            (10, 'AUD'),
+            (5, 'USD'),
+            (2, 'CAD'),
+        ]
+
+        for price, currency in prices:
+
+            stock.models.StockItem.objects.create(
+                part=p,
+                quantity=10,
+                purchase_price=price,
+                purchase_price_currency=currency
+            )
+
+        # Ensure that initially, stock item pricing is disabled
+        common.models.InvenTreeSetting.set_setting('PRICING_USE_STOCK_PRICING', False, None)
+
+        pricing = p.pricing
+        pricing.update_pricing()
+
+        # Check that stock item pricing data is not used
+        self.assertIsNone(pricing.purchase_cost_min)
+        self.assertIsNone(pricing.purchase_cost_max)
+        self.assertIsNone(pricing.overall_min)
+        self.assertIsNone(pricing.overall_max)
+
+        # Turn on stock pricing
+        common.models.InvenTreeSetting.set_setting('PRICING_USE_STOCK_PRICING', True, None)
+
+        pricing.update_pricing()
+
+        self.assertIsNotNone(pricing.purchase_cost_min)
+        self.assertIsNotNone(pricing.purchase_cost_max)
+
+        self.assertEqual(pricing.overall_min, Money(1.176471, 'USD'))
+        self.assertEqual(pricing.overall_max, Money(6.666667, 'USD'))
+
     def test_bom_pricing(self):
         """Unit test for BOM pricing calculations"""