You can now add cost items into a cost schedule, and as sub items to a parent cost item. Thanks myoualid and Jesusbill!

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

@@ -0,0 +1,28 @@
+import ifcopenshell.api
+
+
+class Usecase:
+    def __init__(self, file, **settings):
+        self.file = file
+        self.settings = {"cost_schedule": None, "cost_item": None}
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        cost_item = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcCostItem")
+
+        if self.settings["cost_schedule"]:
+            self.file.create_entity(
+                "IfcRelAssignsToControl",
+                **{
+                    "GlobalId": ifcopenshell.guid.new(),
+                    "OwnerHistory": ifcopenshell.api.run("owner.create_owner_history", self.file),
+                    "RelatedObjects": [cost_item],
+                    "RelatingControl": self.settings["cost_schedule"],
+                }
+            )
+        elif self.settings["cost_item"]:
+            ifcopenshell.api.run(
+                "nest.assign_object", self.file, object=cost_item, relating_object=self.settings["cost_item"]
+            )
+        return cost_item

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

@@ -4,15 +4,19 @@ import ifcopenshell.util.date
 class Data:
     is_loaded = False
     cost_schedules = {}
+    cost_items = {}
 
     @classmethod
     def purge(cls):
         cls.is_loaded = False
         cls.cost_schedules = {}
+        cls.cost_items = {}
 
     @classmethod
     def load(cls, file):
         cls.cost_schedules = {}
+        cls.cost_items = {}
+
         for cost_schedule in file.by_type("IfcCostSchedule"):
             data = cost_schedule.get_info()
             del data["OwnerHistory"]
@@ -20,5 +24,21 @@ class Data:
                 data["SubmittedOn"] = ifcopenshell.util.date.ifc2datetime(data["SubmittedOn"])
             if data["UpdateDate"]:
                 data["UpdateDate"] = ifcopenshell.util.date.ifc2datetime(data["UpdateDate"])
+            data["RelatedObjects"] = []
+            for rel in cost_schedule.Controls:
+                for related_object in rel.RelatedObjects:
+                    if related_object.is_a("IfcCostItem"):
+                        data["RelatedObjects"].append(related_object.id())
+                        break # We are only allowed one summary cost item
             cls.cost_schedules[cost_schedule.id()] = data
+
+        for cost_item in file.by_type("IfcCostItem"):
+            data = cost_item.get_info()
+            del data["OwnerHistory"]
+            del data["CostValues"]
+            del data["CostQuantities"]
+            data["RelatedObjects"] = []
+            for rel in cost_item.IsNestedBy:
+                [data["RelatedObjects"].append(o.id()) for o in rel.RelatedObjects if o.is_a("IfcCostItem")]
+            cls.cost_items[cost_item.id()] = data
         cls.is_loaded=True

src/ifcopenshell-python/ifcopenshell/api/nest/assign_object.py

@@ -0,0 +1,53 @@
+import ifcopenshell
+import ifcopenshell.api
+
+
+class Usecase:
+    def __init__(self, file, **settings):
+        self.file = file
+        self.settings = {
+            "object": None,
+            "relating_object": None,
+        }
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        nests = None
+        if self.settings["object"].Nests:
+            nests = self.settings["object"].Nests[0]
+
+        is_nested_by = None
+        for rel in self.settings["relating_object"].IsNestedBy:
+            if rel.is_a("IfcRelNests"):
+                is_nested_by = rel
+                break
+
+        if nests and nests == is_nested_by:
+            return
+
+        if nests:
+            related_objects = list(nests.RelatedObjects)
+            related_objects.remove(self.settings["object"])
+            if related_objects:
+                nests.RelatedObjects = related_objects
+                ifcopenshell.api.run("owner.update_owner_history", self.file, **{"element": nests})
+            else:
+                self.file.remove(nests)
+
+        if is_nested_by:
+            related_objects = list(is_nested_by.RelatedObjects)
+            related_objects.append(self.settings["object"])
+            is_nested_by.RelatedObjects = related_objects
+            ifcopenshell.api.run("owner.update_owner_history", self.file, **{"element": is_nested_by})
+        else:
+            is_nested_by = self.file.create_entity(
+                "IfcRelNests",
+                **{
+                    "GlobalId": ifcopenshell.guid.new(),
+                    "OwnerHistory": ifcopenshell.api.run("owner.create_owner_history", self.file),
+                    "RelatedObjects": [self.settings["object"]],
+                    "RelatingObject": self.settings["relating_object"],
+                }
+            )
+        return is_nested_by