Refactor previous code for looking up "previous" and "next" serial numbers

- Old way was extremely inefficient, especially when large spaces existed between serial numbers
- New method reduces O(n) to O(1)

InvenTree/stock/models.py

@@ -273,6 +273,55 @@ class StockItem(MPTTModel):
 
         self.serial_int = serial_int
 
+    def get_next_serial_number(self, include_variants=True, reverse=False):
+        """
+        Get the "next" serial number for the part this stock item references.
+
+        e.g. if this stock item has a serial number 100, we may return the stock item with serial number 101
+
+        Note that this only works for "serialized" stock items with integer values
+
+        Args:
+            include_variants: True if we wish to include stock for variant parts
+            reverse: True if we want to return the "previous" (lower) serial number
+
+        Returns:
+            A StockItem object matching the requirements, or None
+
+        """
+
+        if not self.serialized:
+            return None
+
+        # Find only serialized stock items
+        items = StockItem.objects.exclude(serial=None).exclude(serial='')
+
+        if include_variants:
+            # Match against any part within the variant tree
+            items = items.filter(part__tree_id=self.part.tree_id)
+        else:
+            # Match only against the specific part
+            items = items.filter(part=self.part)
+
+        serial = self.serial_int
+
+        if reverse:
+            # Select only stock items with lower serial numbers, in decreasing order
+            items = items.filter(serial_int__lt=serial)
+            items = items.order_by('-serial_int')
+        else:
+            # Select only stock items with higher serial numbers, in increasing order
+            items = items.filter(serial_int__gt=serial)
+            items = items.order_by('serial_int')
+
+        if items.count() > 0:
+            item = items.first()
+
+            if item.serialized:
+                return item
+
+        return None
+
     def save(self, *args, **kwargs):
         """
         Save this StockItem to the database. Performs a number of checks:

InvenTree/stock/views.py

@@ -101,43 +101,16 @@ class StockItemDetail(InvenTreeRoleMixin, DetailView):
     model = StockItem
 
     def get_context_data(self, **kwargs):
-        """ add previous and next item """
+        """
+        Add information on the "next" and "previous" StockItem objects,
+        based on the serial numbers.
+        """
+
         data = super().get_context_data(**kwargs)
 
         if self.object.serialized:
-
+            data['previous'] = self.object.get_next_serial_number(reverse=True)
-            serial_elem = {}
+            data['next'] = self.object.get_next_serial_number()
-
-            try:
-                current = int(self.object.serial)
-
-                for item in self.object.part.stock_items.all():
-
-                    if item.serialized:
-                        try:
-                            sn = int(item.serial)
-                            serial_elem[sn] = item
-                        except ValueError:
-                            # We only support integer serial number progression
-                            pass
-
-                serials = serial_elem.keys()
-
-                # previous
-                for nbr in range(current - 1, min(serials), -1):
-                    if nbr in serials:
-                        data['previous'] = serial_elem.get(nbr, None)
-                        break
-
-                # next
-                for nbr in range(current + 1, max(serials) + 1):
-                    if nbr in serials:
-                        data['next'] = serial_elem.get(nbr, None)
-                        break
-
-            except ValueError:
-                # We only support integer serial number progression
-                pass
 
         data['ownership_enabled'] = common.models.InvenTreeSetting.get_setting('STOCK_OWNERSHIP_CONTROL')
         data['item_owner'] = self.object.get_item_owner()