Query

Small example for getting all Vehicle Components that doesn't have the Deleted or Temp Components (all active vehicles) inside a GameSystemBase which your System should extend from:

this.m_VehicleQuery = this.GetEntityQuery(new EntityQueryDesc() {
    All = new ComponentType[1] {
        ComponentType.ReadOnly<Vehicle>()
    },
    None = new ComponentType[2] {
        ComponentType.ReadOnly<Deleted>(),
        ComponentType.ReadOnly<Temp>()
    }
});

Then you can do things like count the number of found Entities with that matching set:

var count = this.m_VehicleQuery.CalculateEntityCount();