在C#項目中，應對SQL注入問題的最佳方法是使用參數化查詢（Parameterized Query）或預編譯語句（Prepared Statement）

1. 使用SqlCommand和參數化查詢：

using System.Data.SqlClient;

string connectionString = "your_connection_string";
string sqlQuery = "SELECT * FROM Users WHERE Username = @username AND Password = @password";

using (SqlConnection connection = new SqlConnection(connectionString))
{
    using (SqlCommand command = new SqlCommand(sqlQuery, connection))
    {
        // 添加參數并設置值
        command.Parameters.AddWithValue("@username", userInputUsername);
        command.Parameters.AddWithValue("@password", userInputPassword);

        connection.Open();

        using (SqlDataReader reader = command.ExecuteReader())
        {
            // 處理查詢結果
        }
    }
}

2. 使用SqlParameter：

using System.Data.SqlClient;

string connectionString = "your_connection_string";
string sqlQuery = "SELECT * FROM Users WHERE Username = @username AND Password = @password";

using (SqlConnection connection = new SqlConnection(connectionString))
{
    using (SqlCommand command = new SqlCommand(sqlQuery, connection))
    {
        // 創建參數并設置值
        SqlParameter usernameParam = new SqlParameter("@username", SqlDbType.VarChar);
        usernameParam.Value = userInputUsername;

        SqlParameter passwordParam = new SqlParameter("@password", SqlDbType.VarChar);
        passwordParam.Value = userInputPassword;

        // 將參數添加到命令中
        command.Parameters.Add(usernameParam);
        command.Parameters.Add(passwordParam);

        connection.Open();

        using (SqlDataReader reader = command.ExecuteReader())
        {
            // 處理查詢結果
        }
    }
}

3. 使用Dapper庫：

安裝Dapper NuGet包：

Install-Package Dapper

示例代碼：

using System.Data.SqlClient;
using Dapper;

string connectionString = "your_connection_string";
string sqlQuery = "SELECT * FROM Users WHERE Username = @username AND Password = @password";

using (SqlConnection connection = new SqlConnection(connectionString))
{
    connection.Open();

    var queryResult = connection.Query(sqlQuery, new { username = userInputUsername, password = userInputPassword });

    // 處理查詢結果
}

通過使用參數化查詢或預編譯語句，您可以有效地防止SQL注入攻擊，因為參數值會被自動轉義，而不是直接插入到SQL語句中。