Getting EntityCommandBufferSystem.Singleton

[sturdy zodiac]

I am having issues with getting the EntityCommandBufferSystem.Singleton's that unity creates from the create function of my own systems. It works with some systems and other times I get an error say the specific component, in my case specifically EndSimulationEntityCommandBufferSystem.Singleton, does not exist.

Is this due to my system being created before the EndSimulationEntityCommandBufferSystem? If so can I solve this somehow or should I just get the buffer system each time in the update function?

Example of the particular system that is not working for me.

[BurstCompile]
[WorldSystemFilter(WorldSystemFilterFlags.ClientSimulation | WorldSystemFilterFlags.ThinClientSimulation)]
public partial struct MySystem : ISystem
{
    private EntityQuery _query;
    private EndSimulationEntityCommandBufferSystem.Singleton _ecbs;

    [BurstCompile]
    public void OnCreate(ref SystemState state)
    {
        _query = new EntityQueryBuilder(Allocator.Persistent)
            .WithAll<RegularComponent, SharedComponent>()
            .Build(ref state);

        state.RequireForUpdate(_query);
        state.RequireForUpdate<EndSimulationEntityCommandBufferSystem.Singleton>();

        _ecbs = SystemAPI.GetSingleton<EndSimulationEntityCommandBufferSystem.Singleton>();
    }
}

[supple mauve]

the command buffer system creates the singleton in oncreate

so if you're system is created before this point it doesn't exist yet

generally you just grab it in onupdate

if you insist in doing it in oncreate you need to use [CreateAfter(commandbuffersystem)] on all your systems

[sturdy zodiac]

Does the creation order affect update order in any way? Just thinking about other possible effects of doing it this way.

[supple mauve]

no

it only affects create and destroy order

update order is dependent on system groups, updateafter etc

also there's no need to do a
state.RequireForUpdate<EndSimulationEntityCommandBufferSystem.Singleton>();