Allow stock items to be reallocated for build items (#5693)

* Allow stock items to be reallocated for build items

* Refactor create check

* Fix quantity calculation, Add tests

InvenTree/build/serializers.py

@@ -866,10 +866,6 @@ class BuildAllocationItemSerializer(serializers.Serializer):
                 'output': _('Build output cannot be specified for allocation of untracked parts'),
             })
 
-        # Check if this allocation would be unique
-        if BuildItem.objects.filter(build_line=build_line, stock_item=stock_item, install_into=output).exists():
-            raise ValidationError(_('This stock item has already been allocated to this build output'))
-
         return data
 
 
@@ -914,12 +910,16 @@ class BuildAllocationSerializer(serializers.Serializer):
 
                 try:
                     # Create a new BuildItem to allocate stock
-                    BuildItem.objects.create(
+                    build_item, created = BuildItem.objects.get_or_create(
                         build_line=build_line,
                         stock_item=stock_item,
-                        quantity=quantity,
-                        install_into=output
+                        install_into=output,
                     )
+                    if created:
+                        build_item.quantity = quantity
+                    else:
+                        build_item.quantity += quantity
+                    build_item.save()
                 except (ValidationError, DjangoValidationError) as exc:
                     # Catch model errors and re-throw as DRF errors
                     raise ValidationError(detail=serializers.as_serializer_error(exc))

InvenTree/build/test_api.py

@@ -753,6 +753,80 @@ class BuildAllocationTest(BuildAPITest):
         self.assertEqual(allocation.bom_item.pk, 1)
         self.assertEqual(allocation.stock_item.pk, 2)
 
+    def test_reallocate(self):
+        """Test reallocating an existing built item with the same stock item.
+
+        This should increment the quantity of the existing BuildItem object
+        """
+
+        # Find the correct BuildLine
+        si = StockItem.objects.get(pk=2)
+
+        right_line = None
+        for line in self.build.build_lines.all():
+            if line.bom_item.sub_part.pk == si.part.pk:
+                right_line = line
+                break
+
+        self.post(
+            self.url,
+            {
+                "items": [
+                    {
+                        "build_line": right_line.pk,
+                        "stock_item": 2,
+                        "quantity": 3000,
+                    }
+                ]
+            },
+            expected_code=201
+        )
+
+        # A new BuildItem should have been created
+        self.assertEqual(self.n + 1, BuildItem.objects.count())
+
+        allocation = BuildItem.objects.last()
+
+        self.assertEqual(allocation.quantity, 3000)
+        self.assertEqual(allocation.bom_item.pk, 1)
+        self.assertEqual(allocation.stock_item.pk, 2)
+
+        # Try to allocate more than the required quantity (this should fail)
+        self.post(
+            self.url,
+            {
+                "items": [
+                    {
+                        "build_line": right_line.pk,
+                        "stock_item": 2,
+                        "quantity": 2001,
+                    }
+                ]
+            },
+            expected_code=400
+        )
+
+        allocation.refresh_from_db()
+        self.assertEqual(allocation.quantity, 3000)
+
+        # Try to allocate the remaining items
+        self.post(
+            self.url,
+            {
+                "items": [
+                    {
+                        "build_line": right_line.pk,
+                        "stock_item": 2,
+                        "quantity": 2000,
+                    }
+                ]
+            },
+            expected_code=201
+        )
+
+        allocation.refresh_from_db()
+        self.assertEqual(allocation.quantity, 5000)
+
 
 class BuildOverallocationTest(BuildAPITest):
     """Unit tests for over allocation of stock items against a build order.