How can I get a component data from an entity inside a JobComponentSystem?

Questions & Answers
1

I had this system as an ECS, now I am trying to convert it to a job system. My issue is I was using

World.DefaultGameObjectInjectionWorld.EntityManager.GetComponentData<Translation>( hasTarget.targetEntity );

But this does not work inside of JobSystem. I am new to this and would appreciate any help. Since this job runs on multiple entities, I am unsure of how to pass multiple Translation data to the job and I dont understand how the job will know which Translation data corresponds to each entity.

public class UnitMoveToTargetJobSystem : JobComponentSystem
{
    //[ RequireComponentTag( typeof( HasTarget ) ) ]
    [ ExcludeComponent( typeof( InCombat ) ) ]
    [ BurstCompile ]
    private struct MoveToTargetJob : IJobForEachWithEntity<HasTarget , Translation>
    {
        public EntityCommandBuffer.Concurrent entityCommandBuffer;
        public float dt;
        public bool entityHasTarget;

        public void Execute( Entity unitEntity , int index , ref HasTarget hasTarget , ref Translation translation )
        {
            if ( hasTarget.targetEntity != null )
            {
                Translation targetTranslation = World.DefaultGameObjectInjectionWorld.EntityManager.GetComponentData<Translation>( hasTarget.targetEntity );

                float3 targetDirection = math.normalize( targetTranslation.Value - translation.Value );
                float moveSpeed = 8f;
                translation.Value += targetDirection * moveSpeed * dt;

                if ( math.distance( translation.Value , targetTranslation.Value ) <= 0.3f )
                {
                    entityCommandBuffer.AddComponent( index , unitEntity , new InCombat { enemy = hasTarget.targetEntity } );
                    entityCommandBuffer.RemoveComponent( index , unitEntity , typeof( HasTarget ) );

                    //PostUpdateCommands.AddComponent( unitEntity , new InCombat { enemy = hasTarget.targetEntity } );
                    //PostUpdateCommands.RemoveComponent( unitEntity , typeof( HasTarget ) );
                }
            }
            else
            {
                entityCommandBuffer.RemoveComponent( index , unitEntity , typeof( HasTarget ) );

                //PostUpdateCommands.RemoveComponent( unitEntity , typeof( HasTarget ) );
            }
        }
    }

    private EndSimulationEntityCommandBufferSystem endSimulationEntityCommandBufferSystem;
    protected override void OnCreate()
    {
        endSimulationEntityCommandBufferSystem = World.GetOrCreateSystem<EndSimulationEntityCommandBufferSystem>();
        base.OnCreate();
    }

    protected override JobHandle OnUpdate( JobHandle inputDeps )
    {
        MoveToTargetJob moveToTargetJob = new MoveToTargetJob
        {
            entityCommandBuffer = endSimulationEntityCommandBufferSystem.CreateCommandBuffer().ToConcurrent() ,
            dt = Time.DeltaTime
        };

        JobHandle jobHandle = moveToTargetJob.Schedule( this , inputDeps );
        endSimulationEntityCommandBufferSystem.AddJobHandleForProducer( jobHandle );

        return jobHandle;
    }
}
2

One solution is to use ComponentDataFromEntity as demonstrated in the answer to this question.
That allows you to create a lookup for a component for all the entities. In your case, you would probably want [ReadOnly] public ComponentDataFromEntity<LocalToWorld> localToWorldFromEntityToFollow; as a field and initialize it to localToWorldFromEntityToFollow = GetComponentDataFromEntity<LocalToWorld>(true)