SQL查询的转换结果-System.InvalidCastException

Question

I am trying to store the result of a select query. The value being returned is stored as an integer in Sqlite .

I decided to try what was presented in this answer: https://stackoverflow.com/a/870771

My code is currently:

 cmd.CommandText = "SELECT id FROM TVShows WHERE id = @id";
 cmd.Parameters.Add(new SQLiteParameter("@id", id));
 conn.Open();

 object result = ConvertFromDBVal<int>(cmd.ExecuteScalar());


  private T ConvertFromDBVal<T>(object obj)
    {
        if (obj == null || obj == DBNull.Value)
        {
            return default(T); // returns the default value for the type
        }
        else
        {
            return (T)obj;
        }
    }

However, I am receiving the error:

System.InvalidCastException at this line:

return (T)obj;

If I simply try and store the result of cmd.ExecuteScalar()) as an int , I get the same error.

I must admit I don't completely understand this function and so if someone could shed some light on that as well, I'd greatly appreciate it!

Answer 1

Per the comments, you cannot cast a long to an int. By passing in long, you will not have a cast exception.

long result = ConvertFromDBVal<long>(cmd.ExecuteScalar());