Question

您好我一直在为项目创建订单表单，并且难以将日期编号输入到数据行。我有以下代码，但我收到错误'ExecuteReader需要一个开放和可用的连接。连接的当前状态已关闭。'。任何有关这方面的帮助将不胜感激。

 private void cmbSelectDay_SelectedIndexChanged(object sender, EventArgs e)
    {

        //variable for case statement
        int day = 0;

        string Sql = "Select deliveryDayNo from standardOrderDetails order by deliveryDayNo";
        SqlConnection conn = new SqlConnection(connStr);  // ...
        SqlCommand cmd = new SqlCommand(Sql, conn); //there is an error happening here that im not too sure about that would need to be fixed first. but once its fixed this should all work.
        SqlDataReader DR = cmd.ExecuteReader();


            while (DR.Read())
            {
                cmbSelectDay.Items.Add(DR[0]);

            }


                //case statement to take the selected value of the combo box and assign a new value to the variable "day" acordingly.
                switch(cmbSelectDay.SelectedText.ToString())
                {
                    case "Monday":
                        {
                            day = 1;
                            break;
                        }
                    case "Tuesday":
                        {
                            day = 2;
                            break;
                        }
                    case "Wednesday":
                        {
                            day = 3;
                            break;
                        }
                    case "Thursday":
                        {
                            day = 4;
                            break;
                        }
                    case "Friday":
                        {
                            day = 5;
                            break;
                        }
                    case "Saturday":
                        {
                            day = 6;
                            break;
                        }

                }


                // DataRow dr = dsLeprechaun.Tables["standardOrderDetails"].Rows.Find(day);
                DataRow dr = dsLeprechaun.Tables["standardOrderDetails"].Rows.Find(day.ToString());
                dgvOrder.Rows.Add(dr["deliveryDayNo"].ToString());


            lblSelectCategory.Visible = true;
            lstBoxSelectCategory.Visible = true;


    }

Answer 1

所以......打开连接：

using(SqlConnection conn = new SqlConnection(connStr))
using(SqlCommand cmd = new SqlCommand(Sql, conn))
{
    conn.Open();
    using(SqlDataReader DR = cmd.ExecuteReader())
    {
        // consume data
    }
}

您可能还想查看有助于ADO.NET的工具，例如＆＃34; dapper＆＃34; - 例如，如果我假设这个数据是一个字符串，我们可以将所有这些缩短为：

using(SqlConnection conn = new SqlConnection(connStr))
{
    var days = conn.Query<string>(
        "Select deliveryDayNo from standardOrderDetails order by deliveryDayNo"
    ).ToList();
    // now add the items from "days"
}

Answer 2

在调用conn方法之前，您需要打开连接对象ExecuteReader()。

试试这个：

SqlConnection conn = new SqlConnection(connStr); 
SqlCommand cmd = new SqlCommand(Sql, conn); 
conn.Open();                                 //Add this statement
SqlDataReader DR = cmd.ExecuteReader();

Answer 3

你必须打开连接

conn.Open();
using(SqlDataReader reader = cmd.ExecuteReader())
  {
    while(reader.Read())
    {
      //code here
    }
  }

Executereader需要打开连接

3 个答案: