C# SelectMany 错误“无法隐式转换类型‘System.Collections.Generic.List<char> ' 到 'System.Collections.Generic.List<list> ’”</list></char>

Question

Inside of a linq Select I have a SelectMany which is throwing an error

C# SelectMany error " Cannot Implicitly convert type ' System.Collections.Generic.List<char> ' to ' System.Collections.Generic.List<List> ' "

List<Hotel> hotelList = reservations
    .GroupBy(i => i.hotelID)
    .Select(c => new Hotel()
    {
        HotelID = c.First().HotelID,
        HotelName = c.First().HotelName,
        HotelAddress1 = c.First().HotelAddress1,
        HotelAddress2 = c.First().HotelAddress2,
        HotelAddress3 = c.First().HotelAddress3,
        HotelCity = c.First().CCCity,
        HotelPostalCode = c.First().CCZip,
        ReservationNumbers = c.SelectMany( i => i.ReservationNumber).Distinct().ToList()

    }).ToList();

SelectMany automatically converts it to a IEnumerable<char> , and then ToList turns that to List<Char>

i.ReservationNumber is of type String , ReservationNumbers is of type List<string> , c is of type IGrouping<Reservation, int>

What would be a way to force conversion to List<string> or how to make SelectMany to return a IEnumerable<string>

Answer 1

If i.ReservationNumber is of type String , you need to write simply

ReservationNumbers = c.Select( i => i.ReservationNumber).Distinct().ToList()

SelectMany tries to iterate through the elements of ReservationNumber , which, being String , is an IEnumerable<char>