C＃將字符串傳遞給Sqlite參數

Question

我正在嘗試將字符串（函數的輸出）傳遞給SqLite查詢，並用它來更新數據庫。 我收到一個錯誤消息，告訴我字符串不是有效的數據類型。

  IList<string> classList = new List<string>(){ "Saber", "Archer", "Lancer", "Rider",
     "Caster", "Assassin", "Berserker", "Ruler", "Avenger", "Moon Cancer"};
    public string setClass(int uid)
    {
        string newClass;
        int remainder = uid % 10;
        newClass = classList[remainder];
        return(newClass);
    }
    [NadekoCommand, Usage, Description, Aliases]
    public async Task initialiseClasses()
    {
        using (SqliteConnection _db = new SqliteConnection(@"Filename=.\myDb.db"))
        {
            _db.Open();
            string newSQL = "ALTER TABLE DiscordUser ADD Class char";
            SqliteCommand command = new SqliteCommand(newSQL, _db);
            command.ExecuteReader();
            string tempClass = setClass(7);  //temporary input
            newSQL = "UPDATE DiscordUser SET Class = @newClass";
            command.Parameters.Add(new SqliteParameter("@newClass", SqliteType.Text).Value = tempClass);
            command = new SqliteCommand(newSQL, _db);
            command.ExecuteReader();
        }
    }

我正在嘗試將tempClass傳遞到Sqlite查詢中。

Answer 1

1. 在將參數分配給命令后，您正在創建一個新命令，這導致沒有執行參數的命令。
2. 可以重寫參數集合上的Add ，使它更流暢，請參見下面的更改。
3. ExecuteReader應該是ExecuteNonQuery

如果using塊構造代碼，則更容易查看命令實例的范圍。 見下文：

public async Task initialiseClasses()
{
    using (SqliteConnection _db = new SqliteConnection(@"Filename=.\myDb.db"))
    {
        _db.Open();
        string newSQL = "ALTER TABLE DiscordUser ADD Class char";
        using(SqliteCommand command = new SqliteCommand(newSQL, _db))
        {
            command.ExecuteNonQuery();
        }

        string tempClass = setClass(7);  //temporary input
        newSQL = "UPDATE DiscordUser SET Class = @newClass";
        using(SqliteCommand command = new SqliteCommand(newSQL, _db))
        {
            command.Parameters.Add("@newClass", SqliteType.Text).Value = tempClass;
            command.ExecuteNonQuery();
        }
    }
}