Question

When i execute this command on my database i receive sometimes result=null. i want to enter the “else” part when is this happening, but i receive

An unhandled exception of type ‘System.FormatException’ occurred in mscorlib.dll.
Additional information: Input string was not in a correct format.

DB database = new DB();
            int reservedSeats = 0;
            using (database.sqlConnection)
            {
                database.sqlConnection.Open();
                string command = "select SUM(nrLocuri) as result from Rezervari where idRand = @idRand and idShow=@idShow";
                using (SqlCommand cmd = new SqlCommand(command, database.sqlConnection))
                {
                    cmd.Parameters.Add("@idRand", SqlDbType.Int).Value = idRand;
                    cmd.Parameters.Add("@idShow", SqlDbType.Int).Value = idShow;
                    using (SqlDataReader dr = cmd.ExecuteReader())
                    {
                        if (dr.Read())
                            if (dr["result"].ToString() != null)
                                reservedSeats = Convert.ToInt32(dr["result"].ToString());
                            else
                                return totalSeats;
                    }
                }
            }
            return totalSeats-reservedSeats; 

Answer 1

Instead of:

if (dr["result"].ToString() != null)

Do:

if (dr["result"] != DbNull.Value)

When the dr["result"] returns a database null, its value is DbNull.Value – when you try to call Convert.ToInt32 on this value, you get a format exception.