Read data from SQL Server database with c# - sql-server

Question

I have list of BuilderString which I want to contain data
public List<int> IDS = new List<int>();
public List<StringBuilder> Items = new List<StringBuilder>();
What's wrong with this code?
SqlConnection con2 = new SqlConnection("Data Source=aya-PC\\SQLEXPRESS;Initial Catalog=ItemSet;Integrated Security=True");
SqlDataReader rdr2;
SqlCommand cmd2;
con2.Open();
for (int i = 0; i < IDS.Count; i++)
{
cmd2 = new SqlCommand("select item From TransactiontData where idT=#IDS[i]", con2);
cmd2.CommandType = CommandType.Text;
rdr2 = cmd2.ExecuteReader();
SqlParameter param = new SqlParameter();
param.ParameterName = "#IDS[i]"
while (rdr2.Read())
{
Items[i].Append((StringBuilder)rdr2["item"]);
}
}

Answer 1

You need to rearrange your code a bit:
using (SqlConnection con2 = new SqlConnection("Data Source=aya-PC\\SQLEXPRESS;Initial Catalog=ItemSet;Integrated Security=True"))
using (SqlCommand cmd2 = new SqlCommand("select item From TransactiontData where idT = #IDS", con2))
{
// add the paramter to the command
cmd2.Parameter.Add("#IDS", SqlDbType.Int);
con2.Open();
for (int i = 0; i < IDS.Count; i++)
{
// set the parameter value
cmd2.Parameter["#IDS"].Value = IDS[i];
// only *THEN* call ExecuteReader()
using (SqlDataReader rdr2 = cmd2.ExecuteReader())
{
while (rdr2.Read())
{
// **NOT SURE** what you're trying to do here.....
// First of all, you need to just call Items.Add()
// to add new items to the list - and I'm TOTALLY
// UNCLEAR what you're trying to do casting the reader
// value to a StringBuilder.......
//
// Items[i].Append((StringBuilder)rdr2["item"]);
//
// replaced with what *might* make more sense.....
Items.Add(rdr2["item"].ToString());
}
rdr.Close();
}
}
con2.Close();
}
Points to note:
I would recommend to always put your SqlConnection, SqlCommand and SqlDataReader into using() {...} blocks to ensure proper disposal
you need to add your parameter and set its value BEFORE you call .ExecuteReader()!
Since the query itself never changes - there's no point in creating a new SqlCommand on every iteration. Create the command once - and then just set the parameter value (which is the only thing changing) once per iteration

Answer 2

You need to assign the parameter value in the application code rather than within the query. I'm not sure exactly what you are trying to accomplish by casting the column value as a StringBuilder. Assuming that each StringBuilder item is to contain a single string retrieved from a varchar/nvarchar column, the example below will do that.
for (int i = 0; i < IDS.Count; i++)
{
var cmd2 = new SqlCommand("select item From TransactiontData where idT=#IDS", con2);
SqlParameter param = new SqlParameter("#IDS", SqlDbType.Int) { Value = IDS[i] };
var rdr2 = cmd2.ExecuteReader();
while (rdr2.Read())
{
Items.Add(new StringBuilder((string)rdr2["item"]));
}
}