struct C1 {
    public int Id;
}

class TestJobSystem : EcsUnityJobSystem<TestJob, C1> {
    protected override int GetChunkSize (EcsSystems systems) {
        // How many entities will be processed in one chunk.
        // This method will be called each frame.
        return 1000;
    }

    protected override EcsWorld GetWorld (EcsSystems systems) {
        // World for component pools and filter.
        return systems.GetWorld ();
    }
    
    protected override EcsFilter GetFilter (EcsWorld world) {
        // Filter for processing.
        return world.Filter<C1> ().End ();
    }
    
    // Optional additional initialization of job structure.
    protected override void SetData (EcsSystems systems, ref TestJob job) {
        job.DeltaTime = Time.deltaTime;
    }
}

struct TestJob : IEcsUnityJob<C1> {
    public float DeltaTime;
    NativeArray<int> _entities;
    [NativeDisableParallelForRestriction]
    NativeArray<C1> _pool1;
    [NativeDisableParallelForRestriction]
    NativeArray<int> _indices1;

    public void Init (NativeArray<int> entities, NativeArray<C1> pool1, NativeArray<int> indices1) {
        // entities array.
        _entities = entities;
        // dense array of components.
        _pool1 = pool1;
        // sparse indices array of components.
        _indices1 = indices1;
    }

    public void Execute (int index) {
        // We should get entity id from entities collection. 
        var entity = _entities[index];
        // To get access for C1 data.
        var pool1Idx = _indices1[entity];
        var c1 = _pool1[pool1Idx];
        // We can change it.
        c1.Id = (c1.Id + 1) % 10000;
        // And save it back.
        _pool1[pool1Idx] = c1;
    }
}