Fix bug where you could reassign class to another product type and create invalid relationships

src/blenderbim/blenderbim/bim/module/root/ui.py

@@ -52,7 +52,9 @@ class BIM_PT_class(Panel):
                 row.operator("bim.reassign_class", icon="CHECKMARK")
                 row.operator("bim.disable_reassign_class", icon="CANCEL", text="")
                 self.draw_class_dropdowns(
-                    context, root_prop.getIfcPredefinedTypes(context.scene.BIMRootProperties, context)
+                    context,
+                    root_prop.getIfcPredefinedTypes(context.scene.BIMRootProperties, context),
+                    should_draw_product=False,
                 )
             else:
                 data = Data.products[props.ifc_definition_id]
@@ -84,10 +86,11 @@ class BIM_PT_class(Panel):
             op.predefined_type = context.scene.BIMRootProperties.ifc_predefined_type if ifc_predefined_types else ""
             op.userdefined_type = context.scene.BIMRootProperties.ifc_userdefined_type
 
-    def draw_class_dropdowns(self, context, ifc_predefined_types):
+    def draw_class_dropdowns(self, context, ifc_predefined_types, should_draw_product=True):
         props = context.scene.BIMRootProperties
-        row = self.layout.row()
+        if should_draw_product:
-        row.prop(props, "ifc_product")
+            row = self.layout.row()
+            row.prop(props, "ifc_product")
         row = self.layout.row()
         row.prop(props, "ifc_class")
         if ifc_predefined_types:

src/ifcopenshell-python/test/api/root/test_reassign_class.py

@@ -0,0 +1,26 @@
+import test.bootstrap
+import ifcopenshell.api
+
+
+class TestReassignClass(test.bootstrap.IFC4):
+    def test_reassigning_a_simple_class(self):
+        element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
+        new = ifcopenshell.api.run("root.reassign_class", self.file, product=element, ifc_class="IfcSlab")
+        assert len([e for e in self.file]) == 1
+        assert new.id() == 2
+        assert new.is_a("IfcSlab")
+
+    def test_reassigning_a_predefined_type(self):
+        element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
+        new = ifcopenshell.api.run(
+            "root.reassign_class", self.file, product=element, ifc_class="IfcSlab", predefined_type="FLOOR"
+        )
+        assert new.PredefinedType == "FLOOR"
+
+    def test_falling_back_to_userdefined_if_the_predefined_type_cannot_be_reassigned(self):
+        element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
+        new = ifcopenshell.api.run(
+            "root.reassign_class", self.file, product=element, ifc_class="IfcSlab", predefined_type="FOO"
+        )
+        assert new.PredefinedType == "USERDEFINED"
+        assert new.ObjectType == "FOO"