how to check if the value exists in the database from visual studio?

Question

I am making a web form which deletes the selected id from the database. But whenever I run my command I get the following error

NullReferenceRxception was unhandled by the user.

And I'm getting this where I'm using addwithvalues.

This is my code:

con.Open();
string query = "delete from [User] where id ='" + TextBox1.Text + "'";
SqlCommand cmd = new SqlCommand(query, con);
cmd.Parameters.AddWithValue("@id", TextBox1.Text); //this is giving an error
int UserExist = (int)cmd.ExecuteScalar();
if (UserExist > 0)
{
    cmd.ExecuteNonQuery();
    con.Close();
}
else
{
    Label1.Text = "No such id found ";
}

How can I fix this error?

Are you sure the same id that you put in your textbox exits in your database? have you traced your code? Try this as well `TextBox1.Text.Trim()` — Masoud Andalibi, Feb 21 '17 at 07:12
[SQL Injection alert](http://msdn.microsoft.com/en-us/library/ms161953%28v=sql.105%29.aspx) - you should **not** concatenate together your SQL statements - use **parametrized queries** instead to avoid SQL injection - check out [Little Bobby Tables](https://xkcd.com/327/) — marc_s, Feb 21 '17 at 07:40
I am not an sql expert but if the problem really is in the line OP marked, does it even matter what is in the db or which type `id` is? Does `AddWithValue` access the db in any way? Couldn't the problem simply be that there is no `@id` in the query? (Which your answer solves, of course) @Valkyriee — wkl, Feb 21 '17 at 07:46
@wkl yeah it can work that way as well. but this eliminates any unwanted data to be added as Id, a validation before sending to database. — Masoud Andalibi, Feb 21 '17 at 07:51
@wkl here in delete it doesnt really matter, but in insert it'll be very useful ^^ — Masoud Andalibi, Feb 21 '17 at 07:59

score 0 · Answer 1 · answered Feb 21 '17 at 07:15

Use this approach see if its works, i assumed the type of Id is an Integer

using(var cmd1 = new SqlCommand("DELETE FROM User WHERE Id = @Id", conn))
{
    cmd1.Parameters.Add("@Id", SqlDbType.Int).Value = Int.Parse(TextBox1.Text);
    conn.Open();
    cmd1.ExecuteNonQuery();
}

how to check if the value exists in the database from visual studio?

1 Answers1