feat: add TTL index to MongoDB store for automatic expiration (#155)

Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>
Co-authored-by: William Easton <strawgate@users.noreply.github.com>

Author: strawgate

key-value/key-value-aio/src/key_value/aio/stores/mongodb/store.py

@@ -174,8 +174,12 @@ async def _setup_collection(self, *, collection: str) -> None:
 
         new_collection: AsyncCollection[dict[str, Any]] = await self._db.create_collection(name=collection)
 
+        # Index for efficient key lookups
         _ = await new_collection.create_index(keys="key")
 
+        # TTL index for automatic expiration of entries when expires_at is reached
+        _ = await new_collection.create_index(keys="expires_at", expireAfterSeconds=0)
+
         self._collections_by_name[collection] = new_collection
 
     @override

key-value/key-value-sync/src/key_value/sync/code_gen/stores/mongodb/store.py

@@ -181,8 +181,12 @@ def _setup_collection(self, *, collection: str) -> None:
 
         new_collection: Collection[dict[str, Any]] = self._db.create_collection(name=collection)
 
+        # Index for efficient key lookups
         _ = new_collection.create_index(keys="key")
 
+        # TTL index for automatic expiration of entries when expires_at is reached
+        _ = new_collection.create_index(keys="expires_at", expireAfterSeconds=0)
+
         self._collections_by_name[collection] = new_collection
 
     @override