You can now count elements, tasks, and resources parametrically for cost items

src/ifcopenshell-python/ifcopenshell/api/cost/add_cost_item_quantity.py

@@ -14,8 +14,10 @@ class Usecase:
         # This is a bold assumption
         # https://forums.buildingsmart.org/t/how-does-a-cost-item-know-that-it-is-counting-a-controlled-product/3564
         if self.settings["ifc_class"] == "IfcQuantityCount" and self.settings["cost_item"].Controls:
+            count = 0
             for rel in self.settings["cost_item"].Controls:
-                quantity[3] += len(rel.RelatedObjects)
+                count += len(rel.RelatedObjects)
+            quantity[3] = count
         quantities = list(self.settings["cost_item"].CostQuantities or [])
         quantities.append(quantity)
         self.settings["cost_item"].CostQuantities = quantities

src/ifcopenshell-python/ifcopenshell/api/cost/assign_cost_item_quantity.py

@@ -9,7 +9,8 @@ class Usecase:
             self.settings[key] = value
 
     def execute(self):
-        self.quantities = set(self.settings["cost_item"].CostQuantities or [])
+        if self.settings["prop_name"]:
+            self.quantities = set(self.settings["cost_item"].CostQuantities or [])
         for product in self.settings["products"]:
             ifcopenshell.api.run(
                 "control.assign_control",
@@ -17,8 +18,12 @@ class Usecase:
                 related_object=product,
                 relating_control=self.settings["cost_item"],
             )
-            self.add_quantity_from_related_object(product)
-        self.settings["cost_item"].CostQuantities = list(self.quantities)
+            if self.settings["prop_name"]:
+                self.add_quantity_from_related_object(product)
+        if self.settings["prop_name"]:
+            self.settings["cost_item"].CostQuantities = list(self.quantities)
+        else:
+            self.update_cost_item_count()
 
     def add_quantity_from_related_object(self, element):
         if not element.is_a("IfcObject"):
@@ -33,3 +38,21 @@ class Usecase:
         for prop in qto.Quantities:
             if prop.is_a("IfcPhysicalSimpleQuantity") and prop.Name.lower() == self.settings["prop_name"].lower():
                 self.quantities.add(prop)
+
+    def update_cost_item_count(self):
+        # This is a bold assumption
+        # https://forums.buildingsmart.org/t/how-does-a-cost-item-know-that-it-is-counting-a-controlled-product/3564
+        if not self.settings["cost_item"].CostQuantities:
+            return ifcopenshell.api.run(
+                "cost.add_cost_item_quantity",
+                self.file,
+                cost_item=self.settings["cost_item"],
+                ifc_class="IfcQuantityCount",
+            )
+        if len(self.settings["cost_item"].CostQuantities) == 1:
+            quantity = self.settings["cost_item"].CostQuantities[0]
+            if quantity.is_a("IfcQuantityCount"):
+                count = 0
+                for rel in self.settings["cost_item"].Controls:
+                    count += len(rel.RelatedObjects)
+                quantity[3] = count

src/ifcopenshell-python/ifcopenshell/api/cost/unassign_cost_item_quantity.py

@@ -19,7 +19,6 @@ class Usecase:
                         if related_object in self.settings["products"]:
                             self.quantities.remove(quantity)
         self.settings["cost_item"].CostQuantities = list(self.quantities)
-
         for product in self.settings["products"]:
             ifcopenshell.api.run(
                 "control.unassign_control",
@@ -27,3 +26,15 @@ class Usecase:
                 related_object=product,
                 relating_control=self.settings["cost_item"],
             )
+        self.update_cost_item_count()
+
+    def update_cost_item_count(self):
+        # This is a bold assumption
+        # https://forums.buildingsmart.org/t/how-does-a-cost-item-know-that-it-is-counting-a-controlled-product/3564
+        if len(self.settings["cost_item"].CostQuantities) == 1:
+            quantity = self.settings["cost_item"].CostQuantities[0]
+            if quantity.is_a("IfcQuantityCount"):
+                count = 0
+                for rel in self.settings["cost_item"].Controls:
+                    count += len(rel.RelatedObjects)
+                quantity[3] = count