Fix default cache dataloader raise key error on non-existing key

RELEASE.md

@@ -0,0 +1,16 @@
+Release type: patch
+
+Calling `.clean(key)` on default dataloader with non-existing `key` will not throw `KeyError` anymore. Example:
+```python
+from strawberry.dataloader import DataLoader
+
+
+async def load_data(keys):
+    return [str(key) for key in keys]
+
+
+dataloader = DataLoader(load_fn=load_data)
+dataloader.clean(42)  # does not throw KeyError anymore
+```
+
+This is a patch release with no breaking changes.

strawberry/dataloader.py

@@ -84,7 +84,9 @@ def set(self, key: K, value: Future[T]) -> None:
         self.cache_map[self.cache_key_fn(key)] = value
 
     def delete(self, key: K) -> None:
-        del self.cache_map[self.cache_key_fn(key)]
+        cache_key = self.cache_key_fn(key)
+        if cache_key in self.cache_map:
+            del self.cache_map[cache_key]
 
     def clear(self) -> None:
         self.cache_map.clear()

tests/test_dataloaders.py

@@ -301,6 +301,11 @@ async def idx(keys: List[int]) -> List[Tuple[int, int]]:
 
     loader = DataLoader(load_fn=idx, cache=False)
 
+    try:
+        loader.clean(1)  # no effect on non-cached values
+    except Exception as e:
+        raise AssertionError("clean non-cached values does not raise KeyError")
+
     assert await loader.load_many([1, 2, 3]) == [(1, 1), (2, 1), (3, 1)]
 
     loader.clear(1)