Quick and dirty fix for nested provider fields

optimade/server/mappers/entries.py

@@ -88,7 +88,14 @@ def alias_for(cls, field: str) -> str:
         :return: Aliased field as found in PROVIDER_ALIASES + ALIASES
         :rtype: str
         """
-        return dict(cls.all_aliases()).get(field, field)
+        split = field.split(".")
+        prop = split[0]
+        subprop = split[1:] if len(split) > 1 else []
+        alias = dict(cls.all_aliases()).get(prop, None)
+        if alias is not None:
+            return alias + ("." + ".".join(subprop) if subprop else "")
+        else:
+            return field
 
     @classmethod
     def get_required_fields(cls) -> set:

tests/filtertransformers/test_mongo.py

@@ -540,6 +540,7 @@ class MyStructureMapper(BaseResourceMapper):
                 ("A", "D"),
                 ("B", "E"),
                 ("C", "F"),
+                ("_exmpl_nested_field", "nested_field"),
             )
 
         mapper = MyStructureMapper()
@@ -564,6 +565,17 @@ class MyStructureMapper(BaseResourceMapper):
         test_filter = ["A", "elements", "C"]
         self.assertEqual(t.postprocess(test_filter), ["A", "elements", "C"])
 
+        test_filter = {"_exmpl_nested_field.sub_property": {"$gt": 1234.5}}
+        self.assertEqual(
+            t.postprocess(test_filter), {"nested_field.sub_property": {"$gt": 1234.5}}
+        )
+
+        test_filter = {"_exmpl_nested_field.sub_property.x": {"$exists": False}}
+        self.assertEqual(
+            t.postprocess(test_filter),
+            {"nested_field.sub_property.x": {"$exists": False}},
+        )
+
     def test_list_properties(self):
         """ Test the HAS ALL, ANY and optional ONLY queries.