从数据库中删除列表框中的现有项目

Question

I am trying to delete the items within the listbox, which already exists in my database. My listbox is populated by a set of random names, and the ones that are equal to the data from the table rows should be deleted. My code:

        SqlCommand RemoveUserName = new SqlCommand("SELECT * FROM Name WHERE ([Name] = @check)", Con);
        RemoveUserName.Parameters.AddWithValue("@check", listbox1.Items);
        SqlDataReader dr = RemoveUserName.ExecuteReader();
        if (dr.HasRows)
        {
            listBox1.Items.Remove(); // ?? Remove the names which are already in the database

        }
        else
        {
          // remain in listbox
        }

Getting an error in my parameter value and I don't know how to delete the said items.

EDITED my current code:

    SqlCommand RemoveUserName = new SqlCommand("SELECT * FROM Name", Con);
    SqlDataReader dr = RemoveUserName.ExecuteReader();
        while (!dr.Read())
        {
            for (int i = 0; i < listBox1.Items.Count; ++i)
            {
                if (listBox1.Items[i].ToString() == dr["Name"].ToString())
                    listBox1.Items.Remove(listBox1.Items[i]);
            }
        }

Has no error anymore, but is still not functional.

WORKING CODE:

          for (int i = listBox1.Items.Count - 1; i >= 0; --i)
        {
            using (var cmd = new SqlCommand("UPDATE [Name] SET [Name] = Name WHERE [Name] = @name", Con))
            {
                cmd.Parameters.AddWithValue("@name", listBox1.Items[i].ToString());
                if (cmd.ExecuteNonQuery() > 0)
                {
                    listBox1.Items.RemoveAt(i);
                }
          }
        }

Thanks @ LarsTech

Answer 1

It helps to loop backwards through the list in order to avoid indexing issues:

for (int i = listBox1.Items.Count - 1; i >= 0; --i) {
  using (var cmd = new SqlCommand("DELETE FROM [Name] WHERE [Name] = @name", Con)) {
    cmd.Parameters.AddWithValue("@name", listBox1.Items[i].ToString());
    if (cmd.ExecuteNonQuery() > 0) {
      listBox1.Items.RemoveAt(i);
    }
  }
}

ExecuteNonQuery will return the number of records affected, so if it's greater than zero, the name was found and deleted.

Make sure to close your connection object, too. Best by putting it also in a using block the way the SqlCommand object is in my example.

Your table and column names need to be improved.

Answer 2

As I understood,

1) You need to delete items from listbox that already exists in your database and read by SqlDataReader.

You first need to loop into reader. So instead of ! while(reader.Read()) use while(reader.Read())

2) Now you want to remove actual item from listbox, if it exists in reader.

So try to do following to remove item from listbox inside reader while loop

for (int n = listBox.Items.Count - 1; n >= 0; --n)
  {
    var removelistitem = dr["Name"].ToString();
    if (listBox.Items[n].ToString().Contains(removelistitem))
      {
        listBox.Items.RemoveAt(n);
      }
  }

Now after while loop execution. your listbox will only have items not present in your reader (data from database).

Hope this helps.

Edit

Its ok to loop in listbox items.

Use RemoveAt instead. (See above answer)

Answer 3

try this:

    while (!dr.Read())
    {
        for (int i=0; i<listBox1.Items.Count; ++i)
        {
            if (listBox1.Items[i].ToString() == dr["columnName"].ToString())
                listBox1.Items.Remove(listBox1.Items[i]);
        }
    }

SqlReader must be read before use it. If there's no rows in the Reader, code in while block won't be executed.

EDIT I got a problem making you unhappy....

The code you provided:

RemoveUserName.Parameters.AddWithValue("@check", listbox1.Items);

Is wrong, because @check parameter expects string , but you provided was ObjectCollection . Revise query "SELECT * FROM Name WHERE ([Name] = @check)" to "SELECT * FROM Name" . and remove the line AddWithValue .