C# 执行需要打开连接的读卡器
您好,我一直在为一个项目创建一个订单,但很难将日期记录到数据行中。我有下面的代码,但得到错误“ExecuteReader需要一个开放的可用连接。连接的当前状态为关闭。“。在此方面的任何帮助都将不胜感激C# 执行需要打开连接的读卡器,c#,connection-string,C#,Connection String,您好,我一直在为一个项目创建一个订单,但很难将日期记录到数据行中。我有下面的代码,但得到错误“ExecuteReader需要一个开放的可用连接。连接的当前状态为关闭。“。在此方面的任何帮助都将不胜感激 private void cmbSelectDay_SelectedIndexChanged(object sender, EventArgs e) { //variable for case statement int day = 0;
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;
}
在调用
ExecuteReader()
方法之前,需要打开连接对象conn
试试这个:
SqlConnection conn = new SqlConnection(connStr);
SqlCommand cmd = new SqlCommand(Sql, conn);
conn.Open(); //Add this statement
SqlDataReader DR = cmd.ExecuteReader();
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
}
}
您可能还希望研究有助于ADO.NET的工具,例如“dapper”-例如,如果我假设此数据是字符串,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"
}
使用(SqlConnection conn=newsqlconnection(connStr))
{
变量天数=连接查询(
“从standardOrderDetails中选择deliveryDayNo按deliveryDayNo排序”
).ToList();
//现在添加“天”中的项目
}
您必须打开连接
conn.Open();
using(SqlDataReader reader = cmd.ExecuteReader())
{
while(reader.Read())
{
//code here
}
}
嗯,您还没有调用
conn.Open()
来打开连接。。。(您还应该使用和语句,理想情况下使用更高级别的API,但这是另一回事。)还可以使用来处理SqlConnection
、SqlCommand
和SqlDataReader
。您好,我添加了连接,代码似乎运行不正常,但我遇到了另一个错误“对象引用未设置为对象的实例。”。