C＃System.InvalidCastException：'指定的转换无效。' 将MySQL与Discord.Net一起使用时

Question

I've been getting errors which are terrible :D

        public static List<tableName> GetUserStatus(IUser user)
    {
        var result = new List<tableName>();

        var database = new Database("dibot");

        var str = string.Format("SELECT * FROM dibott WHERE userid = '{0}'", user.Id);
        var tableName = database.FireCommand(str);

        while (tableName.Read())
        {
            var userId = (string)tableName["userid"];
            var userName = (string)tableName["username"];
            var currentTokens = (int)tableName["tokens"]; // Here

            result.Add(new tableName
            {
                userid = userId,
                username = userName,
                tokens = currentTokens
            });
        }
        database.CloseConnection();

        return result;

    }

At this command

        [Command("Status")]
    [Alias("status", "s")]
    public async Task Status([Remainder] IUser user = null)
    {
        var embed = new EmbedBuilder()
        {
            Color = new Color(0, 0, 255)
        };
        if (user == null)
        {
            user = Context.User;
        }

        var result = Database.CheckExistingUser(user); //Here

        if (result.Count() <= 0)
        {
            Database.EnterUser(user);
        }

        var tableName = Database.GetUserStatus(user);

I've tried everything please help. I tried much things. Nothing helped Asking for help because im out of ideas and in internet there arent any fixes I've put // To see where are the errors. I hope i get helped soon! :)

Answer 1

So the problematic line is this:

var currentTokens = (int)tableName["tokens"];

InvalidCastException means that the type contained in tableName["tokens"] is not int . To get at the actual type you can for example remove the cast, put a breakpoint on that line and check with the debugger.

From your comment we know that the database type is a varchar, which means you need to use string in .NET:

var currentTokens = (string)tableName["tokens"];

Answer 2

since you are casting tokens into int im assuming its a numeric column.

If you have TINYINT then use byte , if its unsigned then use ubyte
if you have SMALLINT then use short , or ushort if its unsigned
if you have MEDIUMINT/INT then use int or uint for unsigned
if you have BIGINT then use long or ulong for unsigned

best way to find out is to do a tableName["tokens"].GetType() .

If you don't cast it to the right type you will get that InvalidCast exception

Edit:

Based on your comment its a varchar column which means its a string. if you want to make it an int then you need to do

int.Parse((string) tableName["tokens"]);  

or

long.Parse((string) tableName["tokens"]);  

if its a 64 bit int

But it is really a bad design to store numeric in string format and later on parse it again.