Refs #28586 -- Made fetch modes pickle as singletons.

This change ensures that we don’t create new instances of fetch modes
when pickling and unpickling, saving memory and preserving their singleton
nature.

1 files changed, 9 insertions, 0 deletions

diff --git a/django/db/models/fetch_modes.py b/django/db/models/fetch_modes.py
index a22ccd8a23..2b5e6aa212 100644
--- a/django/db/models/fetch_modes.py
+++ b/django/db/models/fetch_modes.py
@@ -16,6 +16,9 @@ class FetchOne(FetchMode):
     def fetch(self, fetcher, instance):
         fetcher.fetch_one(instance)
 
+    def __reduce__(self):
+        return "FETCH_ONE"
+
 
 FETCH_ONE = FetchOne()
 
@@ -36,6 +39,9 @@ class FetchPeers(FetchMode):
         else:
             fetcher.fetch_one(instance)
 
+    def __reduce__(self):
+        return "FETCH_PEERS"
+
 
 FETCH_PEERS = FetchPeers()
 
@@ -48,5 +54,8 @@ class Raise(FetchMode):
         field_name = fetcher.field.name
         raise FieldFetchBlocked(f"Fetching of {klass}.{field_name} blocked.") from None
 
+    def __reduce__(self):
+        return "RAISE"
+
 
 RAISE = Raise()