Select SqlCommand return char

Question

I have got this part of code which do SELECT SqlCommand for column char(20) but the result is always returns 0 - this is because I don't know how to improve my code so it would return char(20) - value which is in this column inserted.

 SqlCommand sc = new SqlCommand("SELECT doklad FROM netpokl WHERE id_dok=" + newIdentity, spojeni);
 spojeni.Open();

 int id_dok = Convert.ToChar(sc.ExecuteScalar());

 spojeni.Close();

 MessageBox.Show("" + id_dok);

 SqlCommand sc2 = new SqlCommand("UPDATE kliplat set doklad=@doklad WHERE id="+newIdentity, spojeni);
 sc2.Parameters.AddWithValue("@doklad", id_dok);

 spojeni.Open();
 sc2.ExecuteNonQuery();
 spojeni.Close();

Would anyone help me improve my code please?

Not an answer to your question but you really need to read about SQL injection. — Dan Pichelman
– Dan Pichelman, Commented Aug 16, 2013 at 21:43
For Parameter better use ADO.Net Parameter (SqlParameter) no Self-made strings - to Dan's answer — BendEg
– BendEg, Commented Aug 16, 2013 at 21:51

King King · Accepted Answer · 2013-08-16 22:04:03Z

4

SqlCommand sc = new SqlCommand(string.Format("SELECT doklad FROM netpokl WHERE id_dok='{0}'", newIdentity), spojeni);
object obj = sc.ExecuteScalar();
if(obj == null) ; //Should show some message or throw exception
string id_dok = obj.ToString().PadRight(20);
//...
SqlCommand sc2 = new SqlCommand(string.Format("UPDATE kliplat set doklad=@doklad WHERE id='{0}'",newIdentity), spojeni);
//...

BTW: I don't think this is needed. In fact you should check if it's length > 20, then the string should be truncated. Your database table should also use nvarchar(20) instead.

edited Aug 16, 2013 at 22:04

answered Aug 16, 2013 at 21:45

King King

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8 Comments

Marek Over a year ago

Hello I tried this but it gave following ex: Reference to an object isn't set to an instance of an object. Any idea where I make mistake?

King King Over a year ago

@Marek this code should replace some lines of yours starting from int id_dok to the end of that line.

Marek Over a year ago

I replaced that as you said but still receiving the same exceptions, don't have any idea where the mistake is.

King King Over a year ago

@Marek at which line it highlights?

Marek Over a year ago

At ´string id_dok = obj.ToString().PadRight(20);´

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