为什么我在asp.net中遇到数据库的连接错误？

I am trying the following code:

我正在尝试以下代码：

SqlConnection con = new SqlConnection();
    con.ConnectionString = Userfunctions.GetConnectionString();
    con.Open();
    for (int i = 0; i < studList.Rows.Count; i++)
    {
        //string a = ((DropDownList)studList.Rows[i].FindControl("actionmenu")).SelectedValue;

            string grade = ((DropDownList)studList.Rows[i].FindControl("actionmenu")).SelectedValue;
            string studentID = studList.Rows[i].Cells[1].Text;
            string courseNumber = MyGlobals.selectedCourse.Substring(MyGlobals.selectedCourse.Length-3);
            string courseCode = MyGlobals.selectedCourse.Substring(0, MyGlobals.selectedCourse.Length - 3);
            SqlCommand com = new SqlCommand("update RegisterTable set Grade=@grade where StudentID=@studentID and CourseCode=@courseCode and CourseNumber=@courseNumber", con);
            com.Parameters.AddWithValue("@grade", grade);
            com.Parameters.AddWithValue("@studentID", studentID);
            com.Parameters.AddWithValue("@courseCode", courseCode);
            com.Parameters.AddWithValue("@courseNumber", courseNumber);
            com.ExecuteNonQuery();

            try
            {
                SqlDataAdapter da2 = new SqlDataAdapter(com);

                DataTable dt2 = new DataTable();
                da2.Fill(dt2);
                DataRow dr2 = dt2.Rows[0];

                Course c = new Course(dr2["InstructorID"].ToString(), dr2["CourseCode"].ToString(), dr2["CourseNumber"].ToString(), dr2["CourseName"].ToString(), dr2["Term"].ToString(), dr2["CRN"].ToString(), dr2["Level"].ToString(), dr2["Credit"].ToString(), dr2["Description"].ToString(), dr2["Capacity"].ToString());
                Register reg = new Register(c, MyGlobals.student);

                MyGlobals.student.dropCourse(reg);

            }
            catch (Exception) { }
            con.Close();

Even though i open the database connection, it gives an error saying that ExecuteNonQuery requires an open and available Connection. The connection's current state is closed. Why is that the case can anyone see? Thanks

即使我打开数据库连接，它也会出现错误，指出ExecuteNonQuery需要一个开放且可用的连接。连接的当前状态已关闭。为什么有人能看到这个案子？谢谢

2 个解决方案

#1

You're closing the connection inside the for-loop, so on the second iteration, the connection isn't open. It should look like this:

您正在关闭for循环内部的连接，因此在第二次迭代中，连接未打开。它应该如下所示：

SqlConnection con = new SqlConnection();
con.ConnectionString = Userfunctions.GetConnectionString();
con.Open();
for (int i = 0; i < studList.Rows.Count; i++)
{
    ...
    SqlCommand com = new SqlCommand(..., con);
    ...
    com.ExecuteNonQuery();

    try
    {
        ...
    }
    catch (Exception) { }
}
con.Close();

#2

You're closing the connection in the loop, so it would move on to the second iteration and the connection would be closed.

您正在关闭循环中的连接，因此它将继续进行第二次迭代，并且将关闭连接。

#1