Datagridview error

Question

I have two datagridviews. So for the second one, i just copy-pasted the code from the first and changed where the difference was. But i get an error at the secod data grid when i want to view the result of my sql code. Translated in english the error show something like that there was no value given to at least one required parameter. Please help! private void button1_Click(object sender, EventArgs e) {

        string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=save.mdb";

        try
        {

           database = new OleDbConnection(connectionString);
           database.Open();
           date =  DateTime.Now.ToShortDateString();
           string queryString = "SELECT zivila.naziv,(obroki_save.skupaj_kalorij/zivila.kalorij)*100 as Kolicina_v_gramih "
               + "FROM (users LEFT JOIN obroki_save ON obroki_save.ID_uporabnika=users.ID)"
               + " LEFT JOIN zivila ON zivila.ID=obroki_save.ID_zivila "
               + " WHERE users.ID= " + a.ToString();
           loadDataGrid(queryString);
       }
       catch (Exception ex)
       {
           MessageBox.Show(ex.Message);
           return;
       }
    }

    public void loadDataGrid(string sqlQueryString)
    {

        OleDbCommand SQLQuery = new OleDbCommand();
        DataTable data = null;
        dataGridView1.DataSource = null;
        SQLQuery.Connection = null;
        OleDbDataAdapter dataAdapter = null;
        dataGridView1.Columns.Clear(); // <-- clear columns

        SQLQuery.CommandText = sqlQueryString;
        SQLQuery.Connection = database;
        data = new DataTable();
        dataAdapter = new OleDbDataAdapter(SQLQuery);
        dataAdapter.Fill(data);
        dataGridView1.DataSource = data;
        dataGridView1.AllowUserToAddRows = false;
        dataGridView1.ReadOnly = true;
        dataGridView1.Columns[0].Visible = true;

    }

    private void Form8_Load(object sender, EventArgs e)
    {

    }

    private void button2_Click(object sender, EventArgs e)
    {
        string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=save.mdb";

        try
        {

            database = new OleDbConnection(connectionString);
            database.Open();
            date = DateTime.Now.ToShortDateString();
            string queryString = "SELECT skupaj_kalorij  "
                + "FROM obroki_save "
                + " WHERE users.ID= " + a.ToString();
            loadDataGrid2(queryString);
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
            return;
        }
    }

    public void loadDataGrid2(string sqlQueryString)
    {

        OleDbCommand SQLQuery = new OleDbCommand();
        DataTable data = null;
        dataGridView2.DataSource = null;
        SQLQuery.Connection = null;
        OleDbDataAdapter dataAdapter = null;
        dataGridView2.Columns.Clear(); // <-- clear columns

        SQLQuery.CommandText = sqlQueryString;
        SQLQuery.Connection = database;
        data = new DataTable();
        dataAdapter = new OleDbDataAdapter(SQLQuery);
        dataAdapter.Fill(data);
        dataGridView2.DataSource = data;
        dataGridView2.AllowUserToAddRows = false;
        dataGridView2.ReadOnly = true;
        dataGridView2.Columns[0].Visible = true;
    }

Answer 1

I think the problem is in private void button2_Click() with

a.ToString();

What's a?

Answer 2

Try putting quotes around a.Tostring():

string queryString = "SELECT zivila.naziv,(obroki_save.skupaj_kalorij/zivila.kalorij)*100 as Kolicina_v_gramih "
               + "FROM (users LEFT JOIN obroki_save ON obroki_save.ID_uporabnika=users.ID)"
               + " LEFT JOIN zivila ON zivila.ID=obroki_save.ID_zivila "
               + " WHERE users.ID= '" + a.ToString() + "'";

or use string.format():

string queryString = string.format("SELECT zivila.naziv,(obroki_save.skupaj_kalorij/zivila.kalorij)*100 as Kolicina_v_gramih "
               + "FROM (users LEFT JOIN obroki_save ON obroki_save.ID_uporabnika=users.ID)"
               + " LEFT JOIN zivila ON zivila.ID=obroki_save.ID_zivila "
               + " WHERE users.ID= '{0}'", a);

Answer 3

You'd be far better off reading and doing this tutorial: http://msdn.microsoft.com/en-us/library/ms171884(v=VS.80).aspx It will probably take about 20 minutes to complete

And then (as needed) the rest of them (google for Data Walkthroughs)

They will teach you how to do your data access properly and, after becoming familiar with the advanced tools in Visual Studio for connecting to databases, you'll be able to generate an app that will show database contents in a grid, and save them back to the db, faster than it took you to even write your post here..

The code will be high performance, more secure and easier to write than what you have here - the code you have here is low quality, prone to SQL injection attacks, not modular or arranged in a way that is suited to the language youre using and takes a long time to write; all in, it has no good points at all (please don't be offended)

I thoroughly recommend scrapping the entire thing and starting again, doing things in the way advocated by Microsoft's tutorial. It might seem like the wrong thing to do after you've poured so many hours into this broken, bad way of doing things, but trust me.. You'll be glad you did; 20 minutes investment now will save you thousands of hours of coding in the future

One final point, if your database data doesnt seem to be saving changes when you do things the way the tutorial tells you to, click on the database in Solution Explorer and change "Copy to Output Directory" to "Copy if Newer" - c# is updating your database but youre either looking in the wrong DB to check whether it worked, or Visual Studio is replacing your edited database with a new one every time you start your app