this is my code,when the textbox content changes the datas required have to retrieved from the databse and displayed in the labels specified.
这是我的代码，当文本框内容发生更改时，必须从数据库中检索所需的数据并显示在指定的标签中。
protected void TextBox1_TextChanged(object sender, EventArgs e)
{
Match match = Regex.Match(TextBox1.Text, @"^\d{4}[A-Z]{5}\d{3}$");
if (match.Success)
{
try
{
DropDownList1.Focus();
string dpt = (string)Session["deptmnt"];
idd = TextBox1.Text;
Label33.Text = idd;
string val = idd;
string con = ConfigurationManager.ConnectionStrings["con"].ConnectionString;
SqlConnection con1 = new SqlConnection(con);
con1.Open();
// string val1 = dpt;
try
{
String str = "SELECT * from student where sid=@val";
SqlCommand cmd = new SqlCommand(str, con1);
cmd.CommandType = CommandType.Text;
SqlParameter sql;
cmd.Parameters.Clear();
sql = cmd.Parameters.Add("@val", SqlDbType.VarChar, 20);
sql.Value = val;
SqlDataReader reader = cmd.ExecuteReader();
if (reader.HasRows == false)
{
Label35.Visible = true;
TextBox1.Text = "";
}
else
{
{
Panel3.Visible = true;
DropDownList1.Focus();
while (reader.Read()) // if can read row from database
{
Panel3.Visible = true;
Label3.Text = reader["sname"].ToString();
Label5.Text = reader["dept"].ToString();
Label25.Text = reader["yr"].ToString();
}
cmd.Parameters.Clear();
{
string val1 = idd;
string str2 = "SELECT bid from studentissuebook where sid=@val1 AND status='" + "lost" + "'";
SqlCommand cmd2 = new SqlCommand(str2, con1);
cmd2.CommandType = CommandType.Text;
cmd2.Parameters.Clear();
SqlParameter sql2;
sql2 = cmd2.Parameters.Add("@val1", SqlDbType.VarChar, 20);
sql2.Value = val1;
SqlDataReader reader1 = cmd2.ExecuteReader();
if (reader1.HasRows == false)
{
TextBox1.Text = "";
Label39.Visible = true;
Panel3.Visible = false;
}
else
{
DropDownList1.Focus();
while (reader1.Read()) // if can read row from database
{
DropDownList1.Items.Add(reader1[0].ToString());
}
DropDownList1.Focus();
}
}
}
}
con1.Close();
}
catch(Exception ex)
{
TextBox1.Text=ex.ToString();
}
}
catch (Exception ex)
{
TextBox1.Text = ex.ToString();
}
} else
{
formatlabel.Visible = true;
}
}
but,when i run the code,i get an error "The variable name '@sid' has already been declared. Variable names must be unique within a query batch or stored procedure.",I googled, generally this error occurs when there is a for loop or any loops,but i do not have any loops in my code.so im unable to find the cause
但是，当我运行代码时，我得到一个错误“变量名称'@sid'已经被声明。变量名在查询批处理或存储过程中必须是唯一的。”，我用Google搜索，通常这个错误发生在有for循环或任何循环，但我的代码中没有任何循环。所以我无法找到原因
1 个解决方案
#1
1
Try using two separate connection and command objects, like this:
尝试使用两个单独的连接和命令对象，如下所示：
protected void TextBox1_TextChanged(object sender, EventArgs e)
{
Match match = Regex.Match(TextBox1.Text, @"^\d{4}[A-Z]{5}\d{3}$");
if (match.Success)
{
DropDownList1.Focus();
string dpt = (string) Session["deptmnt"];
idd = TextBox1.Text;
Label33.Text = idd;
string val = idd;
string con = ConfigurationManager.ConnectionStrings["con"].ConnectionString;
using (SqlConnection con1 = new SqlConnection(con))
{
String str = "SELECT * from student where sid=@val";
con1.Open();
using (SqlCommand cmd = new SqlCommand(str, con1))
{
cmd.CommandType = CommandType.Text;
SqlParameter sql;
cmd.Parameters.Clear();
sql = cmd.Parameters.Add("@val", SqlDbType.VarChar, 20);
sql.Value = val;
SqlDataReader reader = cmd.ExecuteReader();
if (reader.HasRows == false)
{
Label35.Visible = true;
TextBox1.Text = "";
}
else
{
Panel3.Visible = true;
DropDownList1.Focus();
while (reader.Read()) // if can read row from database
{
Panel3.Visible = true;
Label3.Text = reader["sname"].ToString();
Label5.Text = reader["dept"].ToString();
Label25.Text = reader["yr"].ToString();
}
cmd.Parameters.Clear();
}
}
}
using (SqlConnection con2 = new SqlConnection(con))
{
string val1 = idd;
string str2 = "SELECT bid from studentissuebook where sid=@val1 AND status='" + "lost" + "'";
con2.Open();
using (SqlCommand cmd2 = new SqlCommand(str2, con2))
{
cmd2.CommandType = CommandType.Text;
cmd2.Parameters.Clear();
SqlParameter sql2;
sql2 = cmd2.Parameters.Add("@val1", SqlDbType.VarChar, 20);
sql2.Value = val1;
SqlDataReader reader1 = cmd2.ExecuteReader();
if (reader1.HasRows == false)
{
TextBox1.Text = "";
Label39.Visible = true;
Panel3.Visible = false;
}
else
{
DropDownList1.Focus();
while (reader1.Read()) // if can read row from database
{
DropDownList1.Items.Add(reader1[0].ToString());
}
DropDownList1.Focus();
}
}
}
}
else
{
formatlabel.Visible = true;
}
}
Note: I have removed your try-catch blocks to make the code simpler to interpret, once it is working, then please re-apply your try-catch logic where you feel appropriate. Also, I added using blocks for the SqlConnection and SqlCommand objects, this will clean up the connection even if an exception happens.
注意：我已经删除了try-catch块以使代码更易于解释，一旦它工作，那么请在您认为合适的地方重新应用try-catch逻辑。此外，我添加了使用块的SqlConnection和SqlCommand对象，这将清除连接，即使发生异常。
#1
1
Try using two separate connection and command objects, like this:
尝试使用两个单独的连接和命令对象，如下所示：
protected void TextBox1_TextChanged(object sender, EventArgs e)
{
Match match = Regex.Match(TextBox1.Text, @"^\d{4}[A-Z]{5}\d{3}$");
if (match.Success)
{
DropDownList1.Focus();
string dpt = (string) Session["deptmnt"];
idd = TextBox1.Text;
Label33.Text = idd;
string val = idd;
string con = ConfigurationManager.ConnectionStrings["con"].ConnectionString;
using (SqlConnection con1 = new SqlConnection(con))
{
String str = "SELECT * from student where sid=@val";
con1.Open();
using (SqlCommand cmd = new SqlCommand(str, con1))
{
cmd.CommandType = CommandType.Text;
SqlParameter sql;
cmd.Parameters.Clear();
sql = cmd.Parameters.Add("@val", SqlDbType.VarChar, 20);
sql.Value = val;
SqlDataReader reader = cmd.ExecuteReader();
if (reader.HasRows == false)
{
Label35.Visible = true;
TextBox1.Text = "";
}
else
{
Panel3.Visible = true;
DropDownList1.Focus();
while (reader.Read()) // if can read row from database
{
Panel3.Visible = true;
Label3.Text = reader["sname"].ToString();
Label5.Text = reader["dept"].ToString();
Label25.Text = reader["yr"].ToString();
}
cmd.Parameters.Clear();
}
}
}
using (SqlConnection con2 = new SqlConnection(con))
{
string val1 = idd;
string str2 = "SELECT bid from studentissuebook where sid=@val1 AND status='" + "lost" + "'";
con2.Open();
using (SqlCommand cmd2 = new SqlCommand(str2, con2))
{
cmd2.CommandType = CommandType.Text;
cmd2.Parameters.Clear();
SqlParameter sql2;
sql2 = cmd2.Parameters.Add("@val1", SqlDbType.VarChar, 20);
sql2.Value = val1;
SqlDataReader reader1 = cmd2.ExecuteReader();
if (reader1.HasRows == false)
{
TextBox1.Text = "";
Label39.Visible = true;
Panel3.Visible = false;
}
else
{
DropDownList1.Focus();
while (reader1.Read()) // if can read row from database
{
DropDownList1.Items.Add(reader1[0].ToString());
}
DropDownList1.Focus();
}
}
}
}
else
{
formatlabel.Visible = true;
}
}
Note: I have removed your try-catch blocks to make the code simpler to interpret, once it is working, then please re-apply your try-catch logic where you feel appropriate. Also, I added using blocks for the SqlConnection and SqlCommand objects, this will clean up the connection even if an exception happens.
注意：我已经删除了try-catch块以使代码更易于解释，一旦它工作，那么请在您认为合适的地方重新应用try-catch逻辑。此外，我添加了使用块的SqlConnection和SqlCommand对象，这将清除连接，即使发生异常。