fix: implement `for_update` for Single documents

frappe/database/database.py

@@ -549,7 +549,7 @@ class Database(object):
 				return r and [[i[1] for i in r]] or []
 
 
-	def get_singles_dict(self, doctype, debug = False):
+	def get_singles_dict(self, doctype, debug=False, *, for_update=False):
 		"""Get Single DocType as dict.
 
 		:param doctype: DocType of the single object whose value is requested
@@ -560,10 +560,13 @@ class Database(object):
 			account_settings = frappe.db.get_singles_dict("Accounts Settings")
 		"""
 		result = self.query.get_sql(
-			"Singles", filters={"doctype": doctype}, fields=["field", "value"]
+			"Singles",
+			filters={"doctype": doctype},
+			fields=["field", "value"],
+			for_update=for_update,
 		).run()
-		dict_  = frappe._dict(result)
-		return dict_
+
+		return frappe._dict(result)
 
 	@staticmethod
 	def get_all(*args, **kwargs):

frappe/model/document.py

@@ -96,14 +96,11 @@ class Document(BaseDocument):
 			if isinstance(args[0], str):
 				# first arugment is doctype
 				self.doctype = args[0]
+				self.name = self.doctype if len(args) == 1 else args[1]
 
-				if len(args) == 1:
-					# single
-					self.name = self.doctype
-				else:
-					self.name = args[1]
-					self.flags.for_update = kwargs.get("for_update")
-
+				# for_update is set in flags to avoid changing load_from_db signature
+				# since it is used in virtual doctypes and inherited in child classes
+				self.flags.for_update = kwargs.get("for_update")
 				self.load_from_db()
 				return
 
@@ -130,7 +127,9 @@ class Document(BaseDocument):
 		"""Load document and children from database and create properties
 		from fields"""
 		if not getattr(self, "_metaclass", False) and self.meta.issingle:
-			single_doc = frappe.db.get_singles_dict(self.doctype)
+			single_doc = frappe.db.get_singles_dict(
+				self.doctype, for_update=self.flags.for_update
+			)
 			if not single_doc:
 				single_doc = frappe.new_doc(self.doctype, as_dict=True)
 				single_doc["name"] = self.doctype