how to select multiple items from table with listbox

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hello everyone ,dear i have question if you could please help me :)

i want to retrieve data from table with multiple filter that i chose from listbox
i want to use this query in my application

SQL

select * from product where firstname='sam' or firstname ='reachel'

and the name i select is loaded to listbox ,
i tried somehow but wasn't correct
and this is my code of c#

C#

List<string> selecteditmes = new List<string>();
            foreach (int i in listBox1.SelectedIndices)
            {
                selecteditmes.Add(listBox1.Items[i].ToString());

 string smdd = "select * from productvw  where Firstname ='"+ i +"'or Firstname="+i+"";

                SqlDataAdapter sqld = new SqlDataAdapter(smdd, cn);
                cn.Open();

                DataTable dt = new DataTable();
                sqld.Fill(dt);
                dataGridView1.DataSource = dt;
                //dataGridView1.Refresh();
                cn.Close();
            }
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            SqlCommand cmd = new SqlCommand("select Firstname from productvw ", cn);
            cn.Open();
            SqlDataReader dr = cmd.ExecuteReader();
            while (dr.Read())
            {
                string smd = (string)dr["Firstname"].ToString();
                listBox1.Items.Add(smd);
            }
            cn.Close();
        }

Posted 23-Sep-15 3:11am

jame01

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[no name] 23-Sep-15 10:18am

Here you are storing the selected value in a list. Once all the values are stored in the list you can able to get one by one values from there using a loop and compose your query inside that loop. Try to use this concept.

Richard Deeming 23-Sep-15 10:28am

Your code is vulnerable to SQL Injection[^].

NEVER use string concatenation to build a SQL query. ALWAYS use a parameterized query.

gggustafson 23-Sep-15 12:21pm

I believe that sisir is correct

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Olaf Rose · Accepted Answer · 2015-09-24T23:53:00

You could try it like this:

C#

int selectedCounter = listBox1.SelectedItems.Count;

//the next few rows are for pre-constructing the Connection string WITH PARAMETERS
String sqlQuery = "select * from productvw where ";
for (int i = 0; i < selectedCounter; i++)
{
    if(i != 0)
    {
        sqlQuery += " or ";
    }
    sqlQuery += "Firstname = @Fn" + i.toString();
}

using (SqlConnection connection = new SqlConnection(connectionString))
{
    using (SqlCommand command = new SqlCommand(sqlQuery, Connection))
    {
        for (int i = 0; i < selectedCounter; i++)
        {
            command.Parameters.AddWithValue("@Fn"+i.toString();listBox1.SelectedItem[i].Text);
            Connection.Open();
            SqlDataReader reader = command.ExecuteReader();
            while (Reader.Read())
            {
                //do stuff with the reader here
            }
        }
    }
}