refactor: generate naming series preview without DB calls

frappe/core/doctype/document_naming_settings/document_naming_settings.py

@@ -8,7 +8,7 @@ import frappe
 from frappe import _
 from frappe.core.doctype.doctype.doctype import validate_series
 from frappe.model.document import Document
-from frappe.model.naming import NamingSeries, make_autoname
+from frappe.model.naming import NamingSeries, parse_naming_series
 from frappe.permissions import get_doctypes_with_read
 from frappe.utils import cint
 
@@ -173,24 +173,17 @@ class DocumentNamingSettings(Document):
 	def preview_series(self) -> str:
 		"""Preview what the naming series will generate."""
 
-		generated_names = []
 		series = self.try_naming_series
 		if not series:
 			return ""
-
 		try:
 			doc = self._fetch_last_doc_if_available()
-			for _count in range(3):
-				generated_names.append(make_autoname(series, doc=doc))
+			return "\n".join(NamingSeries(series).get_preview(doc=doc))
 		except Exception as e:
 			if frappe.message_log:
 				frappe.message_log.pop()
 			return _("Failed to generate names from the series") + f"\n{str(e)}"
 
-		# Explcitly rollback in case any changes were made to series table.
-		frappe.db.rollback()  # nosemgrep
-		return "\n".join(generated_names)
-
 	def _fetch_last_doc_if_available(self):
 		"""Fetch last doc for evaluating naming series with fields."""
 		try:

frappe/core/doctype/document_naming_settings/test_document_naming_settings.py

@@ -3,7 +3,6 @@
 
 import frappe
 from frappe.core.doctype.document_naming_settings.document_naming_settings import (
-	NAMING_SERIES_PATTERN,
 	DocumentNamingSettings,
 )
 from frappe.model.naming import get_default_naming_series

frappe/model/naming.py

@@ -80,6 +80,17 @@ class NamingSeries:
 
 		return prefix
 
+	def get_preview(self, doc=None) -> List[str]:
+		"""Generate preview of naming series without using DB counters"""
+		generated_names = []
+		for count in range(1, 4):
+
+			def fake_counter(_prefix, digits):
+				return str(count).zfill(digits)
+
+			generated_names.append(parse_naming_series(self.series, doc=doc, number_generator=fake_counter))
+		return generated_names
+
 
 def set_new_name(doc):
 	"""