Function to predict the next purchase order number

InvenTree/order/fixtures/order.yaml

@@ -4,7 +4,7 @@
 - model: order.purchaseorder
   pk: 1
   fields:
-    reference: 0001
+    reference: '0001'
     description: "Ordering some screws"
     supplier: 1
 
@@ -12,7 +12,7 @@
 - model: order.purchaseorder
   pk: 2
   fields:
-    reference: 0002
+    reference: '0002'
     description: "Ordering some more screws"
     supplier: 3
 

InvenTree/order/models.py

@@ -24,7 +24,7 @@ from stock import models as stock_models
 from company.models import Company, SupplierPart
 
 from InvenTree.fields import RoundingDecimalField
-from InvenTree.helpers import decimal2string
+from InvenTree.helpers import decimal2string, increment
 from InvenTree.status_codes import PurchaseOrderStatus, SalesOrderStatus, StockStatus
 from InvenTree.models import InvenTreeAttachment
 
@@ -96,6 +96,44 @@ class PurchaseOrder(Order):
     
     ORDER_PREFIX = "PO"
 
+    @classmethod
+    def getNextOrderNumber(cls):
+        """
+        Try to predict the next order-number
+        """
+
+        if PurchaseOrder.objects.count() == 0:
+            return None
+
+        # We will assume that the latest pk has the highest PO number
+        order = PurchaseOrder.objects.last()
+        ref = order.reference
+
+        if not ref:
+            return None
+
+        tries = set()
+
+        tries.add(ref)
+
+        while 1:
+            new_ref = increment(ref)
+
+            if new_ref in tries:
+                # We are in a looping situation - simply return the original one
+                return ref
+
+            # Check that the new ref does not exist in the database
+            if PurchaseOrder.objects.filter(reference=new_ref).exists():
+                tries.add(new_ref)
+                new_ref = increment(new_ref)
+
+            else:
+                break
+
+        return new_ref
+
+
     def __str__(self):
         return "PO {ref} - {company}".format(ref=self.reference, company=self.supplier.name)
 

InvenTree/order/tests.py

@@ -37,6 +37,12 @@ class OrderTest(TestCase):
 
         self.assertEqual(str(line), "100 x ACME0001 from ACME (for PO 1 - ACME)")
 
+    def test_increment(self):
+
+        next_ref = PurchaseOrder.getNextOrderNumber()
+
+        self.assertEqual(next_ref, '0003')
+
     def test_on_order(self):
         """ There should be 3 separate items on order for the M2x4 LPHS part """