LinkedEntityGroup and DestroyEntity hierarchically

Unity Engine
,
1

I dont understand how LinkedEntityGroup works. I create 2 entities inside SystemBase OnUpdate ForEach, then i create LinkedEntityGroup buffer:

var projectile = ecb.Instantiate(projPrefab.projectilePrefab);
var jointEntity = PhysicsUtils.CreateLockedZAxisJointEntity(projectile, ecb, drawPoints[0]);
var buffer = ecb.SetBuffer<LinkedEntityGroup>(projectile);
buffer.Add(jointEntity);

ecb - is EntityCommandBuffer
When i destroy parent entity projectile - child jointEntity not destroying. Code of destroying:

 Entities
    .ForEach((Entity entity, ref DeathComponent death) =>
    {
        death.destroyAfter -= dt;
        if (death.destroyAfter <= 0f)
        {
            ecb.DestroyEntity(entity);
        }
    }).Schedule();

I check Entity Debugger, parent entity has component LinkedEntityGroup with right child.
What im doing wrong? Why child entity not destroying when i destroy parent entity?

2

I find answer here Destroying a parent entity does not destroy some children (LinkedEntityGroup)
LinkedEntityGroup must contain parent component as well.