ASP.NET catch{} section firing without any Exception - asp.net

Question

I have a little problem.
In this code, always there is catch{} section firing. Even if any exception is thrown. I checked in debugger and no exception is THROWN but somehow code from catch{} is firing and it transfers me to google.com.
If I comment the code from catch{}, Page is running fine.
Someone know why is that? It makes me mad.
Thanks
protected void Button5_Click(object sender, EventArgs e)
{
if (Page.IsValid == true)
{
try
{
conn = new MySqlConnection("Server=localhost;Port=3306;Database=ewidencja;Uid=webuser;Pwd=web1;");
conn.Open();
MySqlDataAdapter mda = new MySqlDataAdapter();
mda.SelectCommand = new MySqlCommand("select id from pacjenci where pesel='" + Session["pesel"].ToString() + "';", conn);
int id_pacjenta = (int)mda.SelectCommand.ExecuteScalar();
int id_lekarza=Int32.Parse(DropDownList1.SelectedValue);
mda.InsertCommand = new MySqlCommand("insert into planowane_wizyty (id_pacjenta, id_lekarza, data_wizyty) values(" + id_pacjenta + ", " + id_lekarza + ", '" + Calendar1.SelectedDate.ToString().Substring(0,10)+" "+ ListBox1.SelectedItem.Value + "');", conn);
if (mda.InsertCommand.ExecuteNonQuery() == 1)
Response.Redirect("wizyty.aspx");
else
Response.Redirect("info.aspx");
}
catch (Exception ex)
{
Response.Redirect("http://www.google.com");
}
}
}

Answer 1

Response.Redirect can throw a ThreadAbortException. This then hits the outer exception handler, triggering the second Response.Redirect.
See Why Response.Redirect causes System.Threading.ThreadAbortException?
More importantly, this is one reason that data access code should not be mixed so tightly with UI behavior. Debugging such code is difficult, unit testing is near impossible, and reusability is low.
It also looks like your query is being constructed via string concatenation, which is vulnerable to SQL injection. Parameterize the query instead.

Answer 2

The overload of Response.Redirect you are using will always try and stop the current thread. This causes the exception you are seeing. System.Threading.ThreadAbortException
There is an overload available: Response.Redirect(string url, bool endResponse) that allows you to control whether to end the current thread using the endResponse parameter.
All that being said, you can catch this specific error and ignore it. The suggestion below is just one of a few solutions you can implement. It all depends on what you are trying to do.
protected void Button5_Click(object sender, EventArgs e)
{
if (Page.IsValid == true)
{
try
{
conn = new MySqlConnection("Server=localhost;Port=3306;Database=ewidencja;Uid=webuser;Pwd=web1;");
conn.Open();
MySqlDataAdapter mda = new MySqlDataAdapter();
mda.SelectCommand = new MySqlCommand("select id from pacjenci where pesel='" + Session["pesel"].ToString() + "';", conn);
int id_pacjenta = (int)mda.SelectCommand.ExecuteScalar();
int id_lekarza=Int32.Parse(DropDownList1.SelectedValue);
mda.InsertCommand = new MySqlCommand("insert into planowane_wizyty (id_pacjenta, id_lekarza, data_wizyty) values(" + id_pacjenta + ", " + id_lekarza + ", '" + Calendar1.SelectedDate.ToString().Substring(0,10)+" "+ ListBox1.SelectedItem.Value + "');", conn);
if (mda.InsertCommand.ExecuteNonQuery() == 1)
Response.Redirect("wizyty.aspx");
else
Response.Redirect("info.aspx");
}
catch (System.Threading.ThreadAbortException)
{
//do nothing. This is an expected error stemming from Response.Redirect
}
catch (Exception ex)
{
Response.Redirect("http://www.google.com");
}
}
}