sdk: Fix empty-cache handling in LocalFileIdentifiableStore (#463)

Previously, the `_object_cache` of the `LocalFileIdentifiableStore` was
initialised empty. Calling `discard()` immediately after store
initialisation raised a `KeyError` if the Identifiable to delete existed
on disk but had not yet been loaded into the in-memory cache.

This adds explicit handling of missing cache entries in `discard()`,
preventing errors when a key is not present in the in-memory cache.
Moreover, a corresponding regression test is added. Finally, the interim
empty-cache workaround in `sync()` is removed.

Fixes #438

Author: moritzsommer

sdk/basyx/aas/backend/local_file.py

@@ -123,7 +123,7 @@ def discard(self, x: model.Identifiable) -> None:
         except FileNotFoundError as e:
             raise KeyError("No AAS object with id {} exists in local file database".format(x.id)) from e
         with self._object_cache_lock:
-            del self._object_cache[x.id]
+            self._object_cache.pop(x.id, None)
 
     def __contains__(self, x: object) -> bool:
         """

sdk/basyx/aas/model/provider.py

@@ -78,20 +78,6 @@ def sync(self, other: Iterable[_VALUE], overwrite: bool) -> Tuple[int, int, int]
         for value in other:
             if value in self:
                 if overwrite:
-
-                    # TODO: This is a quick fix. Yes it works. The underlying problem with the subclass
-                    # `LocalFileIdentifiableStore` will be solved in a separate issue
-                    # (https://github.com/eclipse-basyx/basyx-python-sdk/issues/438).
-                    # Think of this as pythonic duct tape.
-                    #
-                    # The problem is that the `_object_cache` isn't initialised together with the
-                    # `LocalFileIdentifiableStore`, leading to an error when `discard()` is called on the empty cache.
-                    # The for-loop calls `__iter__` calls `get_identifiable_by_hash()` calls
-                    # `self._object_cache[obj.id] = obj`, adding all identifiables to the cache and therefore avoiding
-                    # the error.
-                    for element in self:
-                        pass
-
                     self.discard(value)
                     self.add(value)
                     overwritten += 1

sdk/test/backend/test_local_file.py

@@ -106,3 +106,13 @@ def test_key_errors(self) -> None:
             self.identifiable_store.discard(retrieved_submodel)
         self.assertEqual("'No AAS object with id https://acplt.org/Test_Submodel exists in "
                          "local file database'", str(cm.exception))
+
+    def test_reload_discard(self) -> None:
+        # Load example submodel
+        example_submodel = create_example_submodel()
+        self.identifiable_store.add(example_submodel)
+
+        # Reload the DictIdentifiableStore and discard the example submodel
+        self.identifiable_store = local_file.LocalFileIdentifiableStore(store_path)
+        self.identifiable_store.discard(example_submodel)
+        self.assertNotIn(example_submodel, self.identifiable_store)