如何在数据库中引入数据并在DataGridView中查看日期？

Question

namespace Test
{
    public partial class Form1 : Form
    { 
        OleDbConnection cn;

        private String connParam = @"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Users\Diana\Documents\Visual Studio 2012\Projects\Test\Test\baza.mdb;Persist Security Info=False";
        public Form1()
        {
            cn = new OleDbConnection(connParam);   
            InitializeComponent();
        }  
        DataSet ds;
        OleDbDataAdapter da;

        private void Form1_Load(object sender, EventArgs e)
        {
            cn.Open();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (Convert.ToInt32(textBox1.Text) > 36)
            {          
                MessageBox.Show("Insert a valid data");

                OleDbCommand comm = cn.CreateCommand();
                comm.CommandText = "insert into ins_number (numb) values ('" + this.textBox1.Text + "');";
                comm.ExecuteNonQuery();
                da = new OleDbDataAdapter("select Number,[Red],[Black],[1_18],[19_36],[Even],[Odd],[1Column],[2Column],[3Column],[1Dozen],[2Dozen],[3Dozen] from [number],[ins_number] where number=numb order by [Id_Numb] desc", connParam);
                ds = new DataSet();
                da.Fill(ds);
                dataGridView1.DataSource = ds.Tables[0];        
            }
        }
    }
}

When I click ok, I need first to add data in database and to view dates in dataGridView but I don't see last value which I introduce, I see the first data when I add second. How can I make to view it in the same time when I click ok?

Answer 1

You should really change a lot of things in the code above.

• First, do not keep in class global variables your connection. It is an expensive resource and you should really open, use and release it only when you need it
• Second, you should use parameterized query instead of string concatenations. This will avoid parsing problems, sql injections and your query will be more readable
• Third, embedding the variable name inside the string command doesn't transfor the variable in the actual number, you should also use here the parameterized query approach.

As an example:

private void button1_Click(object sender, EventArgs e)
{
    if (Convert.ToInt32(textBox1.Text) > 36)            
        MessageBox.Show("Insert a valid data");
    else
    {
        using(OleDbConnection cn = new OleDbConnection())
        using(OleDbCommand comm = new OleDbCommand("insert into ins_number (numb) values (?)", cn))
        {
             cn.Open();
             comm.Parameters.AddWithValue("@p1",Convert.ToInt32(this.textBox1.Text));
             comm.ExecuteNonQuery();
             da = new OleDbDataAdapter("select Number,[Red],[Black],[1_18],[19_36],[Even],[Odd],"+ 
                              "[1Column],[2Column],[3Column],[1Dozen],[2Dozen],[3Dozen] " +
                              "from [ins_number] where numb=? order by [Id_Numb] desc");
             da.SelectCommand.Parameters.AddWithValue("@p1", Convert.ToInt32(this.textBox1.Text));
             ds = new DataSet();
             da.Fill(ds);
             dataGridView1.DataSource = ds.Tables[0];        
        }
    }
}

I have moved the global connection variable inside the Click event and enclosed in a using statement. This will close and dispose the connection once used also in case of exceptions. Of course you should remove the global declaration, initialization and openinig in the form_load event.

There are other errors in the query used to fill the datagrid but I cannot be sure what are your intentions here. I have changed your query to retrieve the record just inserted, but if this is not your plan, then change appropriately the WHERE condition.

Also, if you find an error in the input data, then I am sure that you don't want to execute the insert so an else part is needed after the messagebox display....