Resolve nested complex quantity paths in the selector (#2041)

get_element_value could not reach the members of an IfcPhysicalComplexQuantity
(or IfcComplexProperty) by their natural path. util.element expands a complex
quantity into a dict whose nested members live under a "properties" sub-dict,
but the selector's dict navigation only looked at the top level, so
"Qto_Custom.Layer1.Width" returned None and IfcCsv exported nothing for it.
Only the internal "Qto_Custom.Layer1.properties.Width" path worked.

When a key is not a direct member of the value dict, descend into its
"properties" sub-dict so nested quantities/properties resolve with the
natural "Set.Complex.Nested" path. Direct keys still take priority, so the
explicit ".properties." path stays backward compatible and the regex branch
is untouched.

Verified: Qto_Custom.Layer1.Width -> 0.1 and Layer1.Height -> 2.5 (were
None), the sibling simple NetArea still resolves, the legacy .properties.
path still works, and IfcCsv now exports the nested value. test_selector.py:
38 passed (adds test_selecting_a_nested_complex_quantity).

Generated with the assistance of an AI coding tool.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ifcopenshell-python/ifcopenshell/util/selector.py

@@ -540,8 +540,15 @@ def _get_element_value(element: ifcopenshell.entity_instance, keys: list[str]) -
                 value = results or None
                 if value and len(value) == 1:
                     value = value[0]
+            elif key in value:
+                value = value[key]
             else:
-                value = value.get(key, None)
+                # A nested complex quantity/property (IfcPhysicalComplexQuantity /
+                # IfcComplexProperty) is represented as a dict whose nested members
+                # live under a "properties" sub-dict. Descend into it so that nested
+                # values are reachable with the natural "Qto.Complex.Nested" path.
+                subprops = value.get("properties")
+                value = subprops.get(key, None) if isinstance(subprops, dict) else None
         elif isinstance(value, (list, tuple, set)):  # If we use regex
             if isinstance(key, str) and key.isnumeric():
                 try:

src/ifcopenshell-python/test/util/test_selector.py

@@ -195,6 +195,37 @@ class TestGetElementValue(test.bootstrap.IFC4):
         assert subject.get_element_value(element, "/Pset_.*Common/.Status") == ["New"]
         assert subject.get_element_value(element, "/Pset_.*Common/.Status.0") == "New"
 
+    def test_selecting_a_nested_complex_quantity(self):
+        element = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        complex_quantity = self.file.create_entity(
+            "IfcPhysicalComplexQuantity",
+            Name="Layer1",
+            Discrimination="layer",
+            HasQuantities=[
+                self.file.create_entity("IfcQuantityLength", Name="Width", LengthValue=0.1),
+                self.file.create_entity("IfcQuantityLength", Name="Height", LengthValue=2.5),
+            ],
+        )
+        quantity = self.file.create_entity(
+            "IfcElementQuantity",
+            GlobalId=ifcopenshell.guid.new(),
+            Name="Qto_Custom",
+            Quantities=[complex_quantity, self.file.create_entity("IfcQuantityArea", Name="NetArea", AreaValue=5.0)],
+        )
+        self.file.create_entity(
+            "IfcRelDefinesByProperties",
+            GlobalId=ifcopenshell.guid.new(),
+            RelatedObjects=[element],
+            RelatingPropertyDefinition=quantity,
+        )
+        # A simple quantity in the same set still resolves normally.
+        assert subject.get_element_value(element, "Qto_Custom.NetArea") == 5.0
+        # Nested quantities of a complex quantity are reachable with the natural path.
+        assert subject.get_element_value(element, "Qto_Custom.Layer1.Width") == 0.1
+        assert subject.get_element_value(element, "Qto_Custom.Layer1.Height") == 2.5
+        # The explicit "properties" path is preserved for backwards compatibility.
+        assert subject.get_element_value(element, "Qto_Custom.Layer1.properties.Width") == 0.1
+
 
 class TestFilterElements(test.bootstrap.IFC4):
     def test_selecting_by_globalid(self):