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--- globalobjectid [2021/02/08 06:32] – [Prefabs] uninomiconadmin
+++ globalobjectid [2025/01/15 04:35] (current) – external edit 127.0.0.1
@@ Line 5: / Line 5: @@
 GlobalObjectIds are not available at runtime. However, they are available in Play Mode in the editor. If you use these in play mode, keep in mind the notes on prefabs below.
-===== Prefabs =====
+===== Prefabs have two GlobalObjectIds =====
 //All notes below only apply to running the game in Play mode in the Editor.//
-Prefabs Instances have a GID value that is different from the GID assigned when the game is run in Play Mode. When a scene is loaded in play mode, prefabs are merged (unpacked) into standard game-objects. These gameobjects have a different GID than the original prefab. However the GID of the unpacked GameObjects is *still* unique and stable!
+When a scene is loaded in play mode, prefabs are unpacked ((I've seen this mentioned in the profiler as Prefabs.MergePrefabs, during [[scenemanager]] scene loads.)) into standard game-objects. These gameobjects have a different GID than the original prefab. However the GID of the unpacked GameObjects is *still* unique and stable!
-Whatever process that Unity uses to unpack gameobjects((
-I've seen this mentioned in the profiler as Prefabs.MergePrefabs, during [[engine:scenemanager]] scene loads.
-)) must be determinstic, and generate a fileID for the new gameobject that is based on the prefab.
 For example. You may have a prefab in the scene with GID:
@@ Line 23: / Line 19: @@
 ''GlobalObjectId_V1-2-78f49d9837f92464f873c69e2450c95f-4323523526593417776-0''
-(Note how the zero at the end of the second GID implies the object is no longer a prefab, which is correct).
+Note how the zero at the end of the second GID implies the object is no longer a prefab, which is correct. I call these two GlobalObjectIds the 'Prefab GlobalObjectId' and the 'Unpacked GlobalObjectId'.
+==== Converting a Prefab Gid to an Unpacked Gid ====
+You can convert between the two using the following formula:((
+Source: [[https://forum.unity.com/threads/how-is-fileid-generated-for-m_correspondingsourceobject.726704/#post-4851011]]  This is for a slightly different situation, but I have found that the same formula applies to unpacking prefabs
+))
+''%%(%%prefabGid.targetObjectId ^ prefabGid.targetPrefabId) & 0x7fffffffffffffff''
+++++ Example Code|
+<code csharp>
+private static GlobalObjectId ConvertPrefabGidToUnpackedGid(GlobalObjectId id)
+{
+    ulong fileId = (id.targetObjectId ^ id.targetPrefabId) & 0x7fffffffffffffff;
+    bool success = GlobalObjectId.TryParse(
+        $"GlobalObjectId_V1-{id.identifierType}-{id.assetGUID}-{fileId}-0",
+        out GlobalObjectId unpackedGid);
+    Assert.IsTrue(success);
+    return unpackedGid;
+}
+</code>
+++++
+===== Bug: Querying deleted objects =====
+When calling ''GlobalObjectId.GlobalObjectIdentifiersToObjectsSlow'' with a GlobalObjectId that was assigned to a now-deleted object, the Object returned will sometimes be a valid, arbitrary Object in the project, rather than the correct value of ''null''.
+For example, in this case, when passed an array of only scene objects:
+{{ :hdmvjaumtf.png?direct&400 |}}
+The function will return non-scene objects (the shader editor asset at 205).
+{{ :is0bzbpnb6.png?direct&400 |}}
+This seems to be a bug. The correct result should have been ''null'', because that GID was deleted.
-Clearly, some aspects of the prefab are distilled down into the ''4323523526593417776'' fileId portion of the GID. Perhaps it's some hashing of the prefabInstanceId?
+I have had some luck <sup>[//[[:wiki:tag:dark-magic|dark magic]]//]</sup> querying these 'bad' GIDs individually with ''GlobalObjectIdentifierToObjectSlow''. This seems to properly return null in certain cases. This does not cure all cases, however((Luckily, there was only a small set of objects that were valid to be stored by my GIDs, and so I could discard any GIDs resolving to the wrong type.)).
+Update: This is fixed in 2021.1 [[https://issuetracker.unity3d.com/issues/globalobjectidglobalobjectidentifierstoobjectsslow-sometimes-returns-a-random-existing-gameobject|bug tracker]].