From 55e342bbd50a08784dfc6fa46cc9b77be7ccfbdb Mon Sep 17 00:00:00 2001
From: vijayanrxbb <vijayan@rxbb.io>
Date: Fri, 24 Apr 2026 20:02:43 +0530
Subject: [PATCH] test(db_query): assert self-referential Link joins don't
 collide on alias

Mirrors test_ambiguous_linked_tables but with a DocType whose Link
fields point back to itself, covering the path where pypika's '2'
auto-alias collides on the second self-join.
---
 frappe/tests/test_db_query.py | 60 +++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/frappe/tests/test_db_query.py b/frappe/tests/test_db_query.py
index c20b8aa9c1..e25d24a7f0 100644
--- a/frappe/tests/test_db_query.py
+++ b/frappe/tests/test_db_query.py
@@ -1179,6 +1179,66 @@ class TestDBQuery(IntegrationTestCase):
 		data = get()
 		self.assertEqual(len(data["values"]), 1)
 
+	def test_self_referential_link_joins(self):
+		from frappe.desk.reportview import get
+
+		if not frappe.db.exists("DocType", "Self Linked DocType"):
+			frappe.get_doc(
+				{
+					"doctype": "DocType",
+					"custom": 1,
+					"module": "Custom",
+					"name": "Self Linked DocType",
+					"naming_rule": "Random",
+					"autoname": "hash",
+					"fields": [
+						{
+							"label": "Title",
+							"fieldname": "title",
+							"fieldtype": "Data",
+						},
+						{
+							"label": "Parent Ref",
+							"fieldname": "parent_ref",
+							"fieldtype": "Link",
+							"options": "Self Linked DocType",
+						},
+						{
+							"label": "Sibling Ref",
+							"fieldname": "sibling_ref",
+							"fieldtype": "Link",
+							"options": "Self Linked DocType",
+						},
+					],
+				}
+			).insert()
+		else:
+			frappe.db.delete("Self Linked DocType")
+
+		root = frappe.get_doc({"doctype": "Self Linked DocType", "title": "Root"}).insert()
+		sibling = frappe.get_doc({"doctype": "Self Linked DocType", "title": "Sibling"}).insert()
+		frappe.get_doc(
+			{
+				"doctype": "Self Linked DocType",
+				"title": "Child",
+				"parent_ref": root.name,
+				"sibling_ref": sibling.name,
+			}
+		).insert()
+
+		frappe.form_dict.doctype = "Self Linked DocType"
+		frappe.form_dict.fields = [
+			"`tabSelf Linked DocType`.`name`",
+			"`tabSelf Linked DocType`.`parent_ref`",
+			"`tabSelf Linked DocType`.`sibling_ref`",
+			"parent_ref.title as parent_title",
+			"sibling_ref.title as sibling_title",
+		]
+
+		# Shouldn't raise pymysql.err.OperationalError: (1066, "Not unique table/alias: 'tabSelf Linked DocType2'")
+		data = get()
+		self.assertEqual(len(data["values"]), 3)
+
 	def test_select_star_expansion(self):
 		count = frappe.get_list("Language", [{"SUM": 1}, {"COUNT": "*"}], as_list=1, order_by=None)[0]
 		self.assertEqual(count[0], frappe.db.count("Language"))