Question Server World Serialization

What is the recommended way to serialize server worlds (to e.g. save the world state, shut down the server, and then resume later)?

I tried the simple solution of moving all (non-prefab) ghosts to a separate world, serializing them and then moving them back, but got the following error:

ArgumentException: Tried to serialized an Entity reference however entity reference serialization has been explicitly disabled.
Unity.Entities.Serialization.SerializeUtility+ManagedObjectWriterAdapter.Unity.Serialization.Binary.Adapters.IBinaryAdapter<Unity.Entities.Entity>.Serialize (Unity.Collections.LowLevel.Unsafe.UnsafeAppendBuffer* writer, Unity.Entities.Entity value) (at Library/PackageCache/com.unity.entities@0.17.0-preview.41/Unity.Entities/Serialization/SerializeUtility.cs:77)

This seems to have to do with livelink, as not using the subscene workflow avoids this error. (I assume the issue is the entity reference in the SceneTag component, which is a shared component)

Without livelink, I can serialize my ghosts. Is there anything else I need to do besides tell the GhostSendSystem about my loaded ghostIds so they aren't reused? I did this using GhostSendSystem.SetAllocatedGhostId(int), which seems to work fine. Since the function returns false if the ID is already used, this could also be used to make sure that loaded ghostIds are valid before even moving them to the server world (if e.g. loading into a world that already contains some ghosts for some reason).

With the above both the loaded ghost and the newly created one when the client connects are being properly spawned on the client, and values are being correctly (de)serialized (I checked with a simple HealthComponent).

Is there anything wrong with the above approach? I don't need the livelink workflow / subscenes in my usecase so just creating the ghostcollection in the server and client world with GameObjectConversionUtility.ConvertGameObjectHierarchy is fine for me.

Any feedback is appreciated, thanks!

 

Thanks as always for the quick reply, I really appreciate it!

Alright, I will try to work towards getting it working for subscenes then

There are no ghosts present in the scene when I start the game. The only thing in the subscene is the ghostcollection which contains references to my ghost prefab.



When the game starts, these are the prefabs spawned by (I assume) the ghost collection (I did not manually spawn these prefabs!):



As you can see it has a SceneTag, SceneSection component, and is a prefab. I'm not sure if this is an error on my side or I am misunderstanding the ghostcollection workflow.

When spawning a runtime ghost, I get the singleton GhostPrefabCollectionComponent and then the GhostPrefabBuffer, and find the prefab I want to spawn there. (This is based off of the approach in the repository samples)

Since the prefab I am spawning has the SceneTag component (above) it it makes sense that the runtime version also has the SceneTag. I guess I could remove it during spawning to avoid this (like you mentioned), but I thought I would mention it in case this is not intended behavior on your side.

Yes my idea was along the lines of calling GhostSendSystem.SetAllocatedGhostId with increasing IDs until it returns true, meaning the ID would be valid. Or something along those lines, but it seems to solve my problem.

My current project does not use any pre-spawned ghosts, all ghosts are created during runtime (or loaded from a savefile during runtime). So luckily I don't need to deal with this problem (for now), but the insight is nonetheless appreciated and definitely useful for others. I feel like it should be possible to run some self-made system to match loaded ghosts to scene ghosts, like you mentioned.