perf: Ignore amended_from link fields in link field checks

Small perf benefit at not much cost. `amended_from` are *always*
refererring to cancelled documents so there's no need to check these
fields.

frappe/desk/form/linked_with.py

@@ -71,7 +71,7 @@ class SubmittableDocumentTree:
 
 	def get_all_children(self):
 		"""Get all nodes of a tree except the root node (all the nested submitted
-		documents those are present in referencing tables (dependent tables).
+		documents those are present in referencing tables dependent tables).
 		"""
 		while self.to_be_visited_documents:
 			next_level_children = defaultdict(list)
@@ -101,6 +101,10 @@ class SubmittableDocumentTree:
 
 		child_docs = defaultdict(list)
 		for field in referencing_fields:
+			if field["fieldname"] == "amended_from":
+				# perf: amended_from links are always linked to cancelled documents.
+				continue
+
 			links = (
 				get_referencing_documents(
 					parent_dt,

frappe/model/delete_doc.py

@@ -249,6 +249,8 @@ def check_if_doc_is_linked(doc, method="Delete"):
 
 	for lf in link_fields:
 		link_dt, link_field, issingle = lf["parent"], lf["fieldname"], lf["issingle"]
+		if link_field == "amended_from":
+			continue
 
 		try:
 			meta = frappe.get_meta(link_dt)
@@ -258,7 +260,7 @@ def check_if_doc_is_linked(doc, method="Delete"):
 			continue
 
 		if issingle:
-			if frappe.db.get_value(link_dt, None, link_field) == doc.name:
+			if frappe.db.get_single_value(link_dt, link_field) == doc.name:
 				raise_link_exists_exception(doc, link_dt, link_dt)
 			continue