feat: Link fields with UUID datatype in DB (#26625)

Link fields that refer to doctypes with UUID naming will also be UUID.

frappe/database/schema.py

@@ -200,7 +200,12 @@ class DbColumn:
 		self.not_nullable = not_nullable
 
 	def get_definition(self, for_modification=False):
-		column_def = get_definition(self.fieldtype, precision=self.precision, length=self.length)
+		column_def = get_definition(
+			self.fieldtype,
+			precision=self.precision,
+			length=self.length,
+			options=self.options,
+		)
 
 		if not column_def:
 			return column_def
@@ -356,9 +361,20 @@ def validate_column_length(fieldname):
 		frappe.throw(_("Fieldname is limited to 64 characters ({0})").format(fieldname))
 
 
-def get_definition(fieldtype, precision=None, length=None):
+def get_definition(fieldtype, precision=None, length=None, *, options=None):
 	d = frappe.db.type_map.get(fieldtype)
 
+	if (
+		fieldtype == "Link"
+		and options
+		# XXX: This might not trigger if referred doctype is not yet created
+		# This is largely limitation of how migration happens though.
+		# Maybe we can sort by creation and then modified?
+		and frappe.db.exists("DocType", options)
+		and frappe.get_meta(options).autoname == "UUID"
+	):
+		d = ("uuid", None)
+
 	if not d:
 		return
 

frappe/tests/test_db_update.py

@@ -163,6 +163,17 @@ class TestDBUpdate(FrappeTestCase):
 		self.assertIn(varchar, frappe.db.get_column_type(doctype.name, "name"))
 		doc.reload()  # ensure that docs are still accesible
 
+	def test_uuid_link_field(self):
+		uuid_doctype = new_doctype().update({"autoname": "UUID"}).insert()
+		self.assertEqual(frappe.db.get_column_type(uuid_doctype.name, "name"), "uuid")
+
+		link = "link_field"
+		referring_doctype = new_doctype(
+			fields=[{"fieldname": link, "fieldtype": "Link", "options": uuid_doctype.name}]
+		).insert()
+
+		self.assertEqual(frappe.db.get_column_type(referring_doctype.name, link), "uuid")
+
 
 def get_fieldtype_from_def(field_def):
 	fieldtuple = frappe.db.type_map.get(field_def.fieldtype, ("", 0))