public bool CanDelete <T>(T item) where T : IEntity
{
if (typeof(T) == typeof(Aircraft))
{
return(Flights.All(x => x.Aircraft != item as Aircraft));
}
if (typeof(T) == typeof(AcType))
{
return(Lookups.Aircraft.All(x => x.AcType != item as AcType));
}
if (typeof(T) == typeof(Airfield))
{
return(!Flights.Any(x => x.From == item as Airfield || x.To == item as Airfield));
}
return(true);
}