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public class GetOperatingSystemsHandler : IRequestHandler<GetOperatingSystemsQuery, List<LookupDto>>
    {
        private readonly AppDbContext _db;
        public GetOperatingSystemsHandler(AppDbContext db) => _db = db;

        public async Task<List<LookupDto>> Handle(GetOperatingSystemsQuery request)
        {
            return await _db.OperatingSystems
                        .AsNoTracking()
                        .Select(o => new LookupDto(o.Id, o.Name))
                        .ToListAsync();
        }
    }