fix: validate items against source Sales Order in Material Request (#58443)

(cherry picked from commit 62e6e23581)

erpnext/stock/doctype/material_request/material_request.py

@@ -123,6 +123,22 @@ class MaterialRequest(BuyingController):
 	def check_if_already_pulled(self):
 		pass
 
+	def validate_with_previous_doc(self):
+		super().validate_with_previous_doc(
+			{
+				"Sales Order": {
+					"ref_dn_field": "sales_order",
+					"compare_fields": [["company", "="]],
+				},
+				"Sales Order Item": {
+					"ref_dn_field": "sales_order_item",
+					"compare_fields": [["item_code", "="], ["uom", "="], ["conversion_factor", "="]],
+					"is_child_table": True,
+					"allow_duplicate_prev_row_id": True,
+				},
+			}
+		)
+
 	def validate_qty_against_so(self):
 		so_items = {}  # Format --> {'SO/00001': {'Item/001': 120, 'Item/002': 24}}
 		for d in self.get("items"):
@@ -165,6 +181,7 @@ class MaterialRequest(BuyingController):
 
 		self.validate_schedule_date()
 		self.check_for_on_hold_or_closed_status("Sales Order", "sales_order")
+		self.validate_with_previous_doc()
 		self.validate_uom_is_integer("uom", "qty")
 		self.validate_material_request_type()
 

erpnext/stock/doctype/material_request/test_material_request.py

@@ -1064,6 +1064,18 @@ class TestMaterialRequest(ERPNextTestSuite):
 		self.assertEqual(mr.items[0].qty, 5)
 		self.assertEqual(mr.items[1].qty, 5)
 
+	def test_item_change_on_sales_order_row_is_blocked(self):
+		from erpnext.selling.doctype.sales_order.mapper import make_material_request
+		from erpnext.selling.doctype.sales_order.test_sales_order import make_sales_order
+
+		other_item = create_item("_Test MR Item Swap").name
+		so = make_sales_order()
+		mr = make_material_request(so.name)
+		mr.material_request_type = "Purchase"
+		# swapping the fetched item would leave a stale link to the SO row
+		mr.items[0].item_code = other_item
+		self.assertRaises(frappe.ValidationError, mr.insert)
+
 	def test_pending_qty_in_pick_list(self):
 		"""Test for pick list mapped doc qty from partially received Material Request Transfer"""
 		import json