added net weight, user, date etc. generates new document number with year as a prefix, restarts numbering every year

backend/api/models.py

@@ -1,4 +1,4 @@
-from django.db import models
+from django.db import models, transaction
 from django.contrib.auth.models import AbstractUser
 from django.utils import timezone
 
@@ -57,3 +57,18 @@ class Report(models.Model):
 
     def __str__(self):
         return self.name
+
+
+class DocumentCounter(models.Model):
+    year = models.IntegerField(unique=True)
+    last_number = models.IntegerField(default=0)
+
+
+def generate_doc_number(year):
+    with transaction.atomic():
+        counter, _ = DocumentCounter.objects.select_for_update().get_or_create(
+            year=year, defaults={'last_number': 0}
+        )
+        counter.last_number += 1
+        counter.save()
+        return f"{year}-{counter.last_number:06d}"