From a908fa62ba6aab3ff5b27b9550f576804cf7babb Mon Sep 17 00:00:00 2001
From: Dion Moult <dion@thinkmoult.com>
Date: Mon, 24 Oct 2022 13:07:45 +1100
Subject: [PATCH] Loading model elements is now half aware of existing elements
 and will reuse where possible.

---
 src/blenderbim/blenderbim/bim/import_ifc.py | 29 +++++++++++++++++----
 src/blenderbim/blenderbim/tool/model.py     |  1 +
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/src/blenderbim/blenderbim/bim/import_ifc.py b/src/blenderbim/blenderbim/bim/import_ifc.py
index 47305155cf..7de48a607a 100644
--- a/src/blenderbim/blenderbim/bim/import_ifc.py
+++ b/src/blenderbim/blenderbim/bim/import_ifc.py
@@ -177,6 +177,7 @@ class IfcImporter:
         self.settings_2d.set(self.settings_2d.INCLUDE_CURVES, True)
         self.settings_2d.set(self.settings.STRICT_TOLERANCE, True)
         self.project = None
+        self.has_existing_project = False
         self.collections = {}
         self.elements = set()
         self.type_collection = None
@@ -893,6 +894,11 @@ class IfcImporter:
         if element is None:
             return
 
+        if self.has_existing_project:
+            obj = tool.Ifc.get_object(element)
+            if obj:
+                return obj
+
         self.ifc_import_settings.logger.info("Creating object %s", element)
 
         if mesh:
@@ -1306,7 +1312,13 @@ class IfcImporter:
                 )
 
     def create_project(self):
-        self.project = {"ifc": self.file.by_type("IfcProject")[0]}
+        project = self.file.by_type("IfcProject")[0]
+        self.project = {"ifc": project}
+        obj = tool.Ifc.get_object(project)
+        if obj:
+            self.project["blender"] = obj.users_collection[0]
+            self.has_existing_project = True
+            return
         self.project["blender"] = bpy.data.collections.new(
             "{}/{}".format(self.project["ifc"].is_a(), self.project["ifc"].Name)
         )
@@ -1359,10 +1371,17 @@ class IfcImporter:
         for element in related_objects:
             if element not in self.spatial_elements:
                 continue
-            global_id = element.GlobalId
-            collection = bpy.data.collections.new(self.get_name(element))
-            self.collections[global_id] = collection
-            parent.children.link(collection)
+            is_existing = False
+            if self.has_existing_project:
+                obj = tool.Ifc.get_object(element)
+                if obj:
+                    is_existing = True
+                    collection = obj.users_collection[0]
+                    self.collections[element.GlobalId] = collection
+            if not is_existing:
+                collection = bpy.data.collections.new(self.get_name(element))
+                self.collections[element.GlobalId] = collection
+                parent.children.link(collection)
             if element.IsDecomposedBy:
                 for rel_aggregate in element.IsDecomposedBy:
                     self.create_spatial_decomposition_collection(collection, rel_aggregate.RelatedObjects)
diff --git a/src/blenderbim/blenderbim/tool/model.py b/src/blenderbim/blenderbim/tool/model.py
index 24a1855b80..ba41199edd 100644
--- a/src/blenderbim/blenderbim/tool/model.py
+++ b/src/blenderbim/blenderbim/tool/model.py
@@ -62,6 +62,7 @@ class Model(blenderbim.core.tool.Model):
         ifc_importer.file = tool.Ifc.get()
         ifc_importer.calculate_unit_scale()
         ifc_importer.process_context_filter()
+        ifc_importer.material_creator.load_existing_materials()
         openings = set(openings)
         openings -= ifc_importer.create_products(openings)
         for opening in openings or []: