关闭读取器时调用读取的尝试无效

本文关键字：读取 无效 调用 | 更新日期: 2023-09-27 17:56:29

我正在对查询运行DbDataReader，以从下拉列表中删除项目（如果它们已附加到特定提交），并且我不断收到错误告诉我阅读器已关闭。不明白为什么我的读者在这里被视为关闭。我错过了什么？

 protected void Page_Load(object sender, EventArgs e)
{
    string x = Request.QueryString["SubId"];
    string connectionString = System.Configuration.ConfigurationManager.
        ConnectionStrings["MyConnectionString"].ConnectionString;
    string displayQuery = "SELECT CustName, CustAdd, CustCity, CustState, " +
        "CustZip FROM Customer WHERE SubId =" + x;
    string broQuery = "SELECT EntityType FROM Broker WHERE SubId =" + x;
    string ddlQuery = "SELECT ProductId FROM SubmissionProducts " +
        "WHERE SubmissionId =" + x;
    using (SqlConnection displayConn = new SqlConnection(connectionString))
    {
        displayConn.Open();
        SqlCommand DlistCmd = new SqlCommand(ddlQuery, displayConn);
        using (SqlDataReader Ddldr = DlistCmd.ExecuteReader())
        {
            while (Ddldr.Read())
            {
                switch (Ddldr.GetInt32(0))
                {
                    case 1:
                        DdlProductList.Items.RemoveAt(1);
                        break;
                    case 2:
                        DdlProductList.Items.RemoveAt(2);
                        break;
                    case 3:
                        DdlProductList.Items.RemoveAt(3);
                        break;
                    case 4:
                        DdlProductList.Items.RemoveAt(4);
                        break;
                    case 5:
                        DdlProductList.Items.RemoveAt(5);
                        break;
                    case 6:
                        DdlProductList.Items.RemoveAt(6);
                        break;
                    case 7:
                        DdlProductList.Items.RemoveAt(7);
                        break;
                    default:
                        break;
                }
                Ddldr.Close();
            }
        }

关闭读取器时调用读取的尝试无效

不要调用Ddldr.Close();，尤其是在while内部。通过这种方式，您正在执行第一次迭代，关闭阅读器，第二次迭代当然会在阅读器关闭时发出嘘声。using声明将处理它。只需从代码中删除此行即可。

所以：

using (SqlDataReader Ddldr = DlistCmd.ExecuteReader())
{
    while (Ddldr.Read())
    {
        switch (Ddldr.GetInt32(0))
        {
            ... your cases here
            default:
                break;
        }
    }
}

还有以下几行：

string x = Request.QueryString["SubId"];
string displayQuery = "SELECT CustName, CustAdd, CustCity, CustState, CustZip FROM Customer WHERE SubId =" + x;
string broQuery = "SELECT EntityType FROM Broker WHERE SubId =" + x;
string ddlQuery = "SELECT ProductId FROM SubmissionProducts WHERE SubmissionId =" + x;

臭得像一堆s.。t.您应该使用参数化查询，绝对不要编写任何这样的代码，否则您的应用程序将容易受到SQL注入的影响。每次在编写 SQL 查询时使用字符串串联时，都会响起警报，告诉您做错了。

因此，这是正确的方法：

protected void Page_Load(object sender, EventArgs e)
{
    string x = Request.QueryString["SubId"];
    string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;
    using (var conn = new SqlConnection(connectionString))
    using (var cmd = conn.CreateCommand())
    {
        conn.Open();
        cmd.CommandText = "SELECT ProductId FROM SubmissionProducts WHERE SubmissionId = @SubmissionId";
        cmd.Parameters.AddWithValue("@SubmissionId", x)
        using (var reader = cmd.ExecuteReader())
        {
            while (Ddldr.Read())
            {
                switch (reader.GetInt32(reader.GetOrdinal("ProductId")))
                {
                    ... your cases here
                    default:
                        break;
                }
            }
        }
    }
}

删除此行：

Ddldr.Close();
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