Entity system following an object

Questions & Answers
,
1

I have many object to follow a main object. Is there way to easily access position of entity or find the entity from code Here is my code:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

using Unity.Entities;
using Unity.Jobs;
using Unity.Mathematics;
using Unity.Physics;
using Unity.Transforms;
using Unity.Burst;

[BurstCompile]
[UpdateInGroup(typeof(FixedStepSimulationSystemGroup))]
public class BallFollowController : SystemBase
{

    /*
    protected override JobHandle OnUpdate(JobHandle inputDeps)
    {
        float deltaTime = Time.DeltaTime;

        Entities.ForEach((ref Translation translation, in BallMainData data) => {
            //translation.Value.z += data.speed * deltaTime;
            temp = translation.Value;
        }).Run();
        var jobHandle = Entities.ForEach((ref PhysicsVelocity velocity,in Translation translation, in BallFollowData data) => {
            velocity.Linear += (temp - translation.Value)*data.speed*deltaTime;

        }).Schedule(inputDeps);
        
    }
    */
    protected override void OnUpdate()
    {
        float deltaTime = Time.DeltaTime;

        
        Entities.ForEach((ref PhysicsVelocity velocity, in Translation translation, in BallFollowData data) => {
            float3 temp = new float3();
            Entities.ForEach((ref Translation translation, in BallMainData data) => {
                //translation.Value.z += data.speed * deltaTime;
                temp = translation.Value;
            }).Run();
            velocity.Linear += (temp - translation.Value) * data.speed * deltaTime;

        }).Schedule();
    }
}
3 
using Unity.Entities;
using Unity.Jobs;
using Unity.Mathematics;
using Unity.Physics;
using Unity.Transforms;
using Unity.Collections;
  
[UpdateInGroup( typeof(FixedStepSimulationSystemGroup) )]
public class BallFollowerSystem : SystemBase
{
	EntityQuery _query;
  
	protected override void OnCreate ()
	{
		_query = EntityManager.CreateEntityQuery( typeof(Translation) , typeof(BallMainData) );
	}
  
	protected override void OnUpdate ()
	{
		float deltaTime = Time.DeltaTime;
		var mainBallPositions = _query.ToComponentDataArray<Translation>( Allocator.TempJob );
		
		Entities
			.WithReadOnly( mainBallPositions ).WithDisposeOnCompletion( mainBallPositions )
			.ForEach( ( ref PhysicsVelocity velocity , in Translation translation , in BallFollowData data ) =>
			{
				for( int i=mainBallPositions.Length-1 ; i!=-1 ; i-- )
				{
					float3 ballPos = mainBallPositions*.Value;
					float3 ballDir = math.normalize( ballPos - translation.Value );
					velocity.Linear += ballDir * data.speed * deltaTime;
				}
			} )
			.WithBurst()
			.ScheduleParallel();
	}
}