From 2cbe3c61beef30158b86210ec72ba0e5eb6dff9c Mon Sep 17 00:00:00 2001
From: David Graves <dgraves@lrtcapitalgroup.com>
Date: Wed, 30 Mar 2022 23:31:10 -0500
Subject: [PATCH] raise ImproperlyConfigured if basename already exists

---
 rest_framework/routers.py | 17 ++++++++++++++++-
 tests/test_routers.py     | 14 ++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/rest_framework/routers.py b/rest_framework/routers.py
index e0ae24b95..3a0eb87e7 100644
--- a/rest_framework/routers.py
+++ b/rest_framework/routers.py
@@ -52,12 +52,27 @@ class BaseRouter:
     def register(self, prefix, viewset, basename=None):
         if basename is None:
             basename = self.get_default_basename(viewset)
-        self.registry.append((prefix, viewset, basename))
+
+        if not self.basename_already_registered(basename):
+            self.registry.append((prefix, viewset, basename))
 
         # invalidate the urls cache
         if hasattr(self, '_urls'):
             del self._urls
 
+    def basename_already_registered(self, new_basename):
+        """
+        If `basename` is already registered, raise an exception
+        """
+        for route in self.registry:
+            prefix, viewset, basename = route
+            if new_basename == basename:
+                msg = (f'Route with basename "{new_basename}" is already registered. '
+                       f'Please provide a unique basename for viewset "{viewset}"')
+                raise ImproperlyConfigured(msg)
+
+        return False
+
     def get_default_basename(self, viewset):
         """
         If `basename` is not specified, attempt to automatically determine
diff --git a/tests/test_routers.py b/tests/test_routers.py
index f767a843d..2ef2bd541 100644
--- a/tests/test_routers.py
+++ b/tests/test_routers.py
@@ -481,3 +481,17 @@ class TestViewInitkwargs(URLPatternsTestCase, TestCase):
         initkwargs = match.func.initkwargs
 
         assert initkwargs['basename'] == 'routertestmodel'
+
+
+class TestDuplicateBasename(URLPatternsTestCase, TestCase):
+    def test_exception_for_duplicate_basename(self):
+        class NoteViewSet(viewsets.ModelViewSet):
+            queryset = RouterTestModel.objects.all()
+
+        self.router = SimpleRouter(trailing_slash=False)
+        self.router.register(r'notes', NoteViewSet)
+
+        with pytest.raises(ImproperlyConfigured):
+            self.router.register(r'notes_duplicate', NoteViewSet)
+
+        self.router.register(r'notes_duplicate_2', NoteViewSet, basename='note_duplicate')
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