fix: added merchant_id in models of shipment module

printing/handlers.py

@@ -114,8 +114,22 @@ def on_printing_job_process_completed(sender, **kwargs):
     
     try:
         with transaction.atomic():
+            # SalesItem.merchant 不允许为空，优先取 printing_job.merchant
+            sales_merchant = getattr(printing_job, 'merchant', None)
+            if not sales_merchant and getattr(printing_job, 'printing_order', None):
+                sales_merchant = getattr(printing_job.printing_order, 'merchant', None)
+            if not sales_merchant and last_completed_by and hasattr(last_completed_by, 'employee'):
+                sales_merchant = getattr(last_completed_by.employee, 'merchant', None)
+            if not sales_merchant:
+                logger.warning(
+                    f'PrintingJob #{printing_job.id} 流程完成，'
+                    f'但无法确定 merchant，跳过销售品创建'
+                )
+                return
+
             sales_item = SalesItem.objects.create(
                 shipment=None,  # 暂不关联出货单，待后续分配
+                merchant=sales_merchant,
                 name=product_name,
                 quantity=quantity,
                 unit=sales_unit,