Unable to cast object of type 'System.Collections.Generic.List to type 'System.Collections.Generic.ICollection

Question

I am trying to assign data to a class, but when executing the method it shows me the error:

Unable to cast object of type 'System.Collections.Generic.List to type 'System.Collections.Generic.ICollection

The procedure I am doing is the following:

I have the TicketData class, which among its fields has an ICollection of the Message class.

public partial class TicketData
{
    public int IdTicket { get; set; }
    public int? IdUser { get; set; }
    public ICollection<Message> Message { get; set; }
}

To assign the values to the TicketData class I obtain the values of the Ticket and Message class.

public class Ticket
{
    public int IdTicket { get; set; }
    public int? IdUser { get; set; }
}

public class Message
{
    public int IdTicket { get; set; }
    public int? IdMessage { get; set; }
    public string Text { get; set; }
}

I do this with the following methods:

var detail = await _unitOfWork.TicketsRepository.GetDetailsTicketRepository(Id);

var messageService = await _unitOfWork.MessageRepository.GetMessagesTicketRepository(Id);

List<VMessages> listMessages = messageService.ToList();

Inside VMessages is identical to class Message.

Then I manually assign the values with:

var TData = new TicketData()
{
    IdTicket = detail.IdTicket,
    IdUser = detail.IdUser,
    Message = (ICollection<Message>)listMessages
};

But this is where it shows me the error described above. If I assign only the values of IdTicket and IdUser it works fine, but when I assign the listMessages to Message it displays the error.

Please can you tell me where I am failing, thank you.

Answer 1

Although VMessage may contain the same members as Message , they are different and unrelated types, so you cannot cast from one to the other in C#.

What you need to do is convert each VMessage to a Message .

One way is to use LINQ:

var convertMessages = listMessages.Select(x => new Message
{
    IdTicket = x.IdTicket,
    IdMessage = x.IdMessage,
    Text = x.Text,
});

var TData = new TicketData()
{
    IdTicket = detail.IdTicket,
    IdUser = detail.IdUser,
    Message = convertMessages.ToArray(),
};

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If this is something that you need to do regularly, you could always use a reflection-based mapping API to reduce boilerplate.