From f9bfbfec9843cf3c38c3dbc8b203cc2fcaeb69ca Mon Sep 17 00:00:00 2001
From: Sagar Vora <sagar@resilient.tech>
Date: Fri, 5 Aug 2022 06:22:37 +0000
Subject: [PATCH] perf: reduce DB calls made in `get_fetch_values` (#17671)

* perf: reduce DB calls made in `get_fetch_values`

* fix: ensure return value is same as before

* test: add test for `frappe.model.utils.get_fetch_values`
---
 frappe/model/utils/__init__.py   | 43 ++++++++++++++++++++++++++------
 frappe/tests/test_model_utils.py | 28 +++++++++++++++++++++
 2 files changed, 63 insertions(+), 8 deletions(-)
 create mode 100644 frappe/tests/test_model_utils.py

diff --git a/frappe/model/utils/__init__.py b/frappe/model/utils/__init__.py
index 1445999639..2220b3904f 100644
--- a/frappe/model/utils/__init__.py
+++ b/frappe/model/utils/__init__.py
@@ -90,15 +90,42 @@ def get_fetch_values(doctype, fieldname, value):
 	:param fieldname: Link fieldname selected
 	:param value: Value selected
 	"""
-	out = {}
-	meta = frappe.get_meta(doctype)
-	link_df = meta.get_field(fieldname)
-	for df in meta.get_fields_to_fetch(fieldname):
-		# example shipping_address.gistin
-		link_field, source_fieldname = df.fetch_from.split(".", 1)
-		out[df.fieldname] = frappe.db.get_value(link_df.options, value, source_fieldname)
 
-	return out
+	result = frappe._dict()
+	meta = frappe.get_meta(doctype)
+
+	# fieldname in target doctype: fieldname in source doctype
+	fields_to_fetch = {
+		df.fieldname: df.fetch_from.split(".", 1)[1] for df in meta.get_fields_to_fetch(fieldname)
+	}
+
+	# nothing to fetch
+	if not fields_to_fetch:
+		return result
+
+	# initialise empty values for target fields
+	for target_fieldname in fields_to_fetch:
+		result[target_fieldname] = None
+
+	# fetch only if Link field has a truthy value
+	if not value:
+		return result
+
+	db_values = frappe.db.get_value(
+		meta.get_options(fieldname),  # source doctype
+		value,
+		tuple(set(fields_to_fetch.values())),  # unique source fieldnames
+		as_dict=True,
+	)
+
+	# if value doesn't exist in source doctype, get_value returns None
+	if not db_values:
+		return result
+
+	for target_fieldname, source_fieldname in fields_to_fetch.items():
+		result[target_fieldname] = db_values.get(source_fieldname)
+
+	return result
 
 
 @site_cache(maxsize=128)
diff --git a/frappe/tests/test_model_utils.py b/frappe/tests/test_model_utils.py
new file mode 100644
index 0000000000..95e3e714a7
--- /dev/null
+++ b/frappe/tests/test_model_utils.py
@@ -0,0 +1,28 @@
+import unittest
+
+import frappe
+from frappe.model.utils import get_fetch_values
+
+
+class TestModelUtils(unittest.TestCase):
+	def test_get_fetch_values(self):
+		doctype = "ToDo"
+
+		# no fields to fetch
+		self.assertEqual(get_fetch_values(doctype, "role", "System Manager"), {})
+
+		# no value
+		self.assertEqual(get_fetch_values(doctype, "assigned_by", None), {"assigned_by_full_name": None})
+
+		# no db values
+		self.assertEqual(
+			get_fetch_values(doctype, "assigned_by", "~not-a-user~"), {"assigned_by_full_name": None}
+		)
+
+		# valid db values
+		user = "test@example.com"
+		full_name = frappe.db.get_value("User", user, "full_name")
+
+		self.assertEqual(
+			get_fetch_values(doctype, "assigned_by", user), {"assigned_by_full_name": full_name}
+		)