C# Windows 窗体应用程序 - 在文本框中显示 sql server 值

Question

I need assistance to display sql server values in a windows forms. In the application below if the query returns a row then the values are displayed. I understand that I am to use sqldatareader but so far I have been unsuccessful how to add it.

SqlConnection ChuoDB_Connection = new SqlConnection("Data Source=test-PC\\tester;Initial Catalog=Chuo;Integrated Security=True;Pooling=False");

    SqlDataAdapter select_adapt;

private void btn_guardian_student_search_Click(object sender, EventArgs e)
    {
        if (rd_btn_guardian_student_no.Checked == true)

        {
            DataSet ds = new DataSet();
            SqlDataReader dr;
            ChuoDB_Connection.Open();
select_adapt = new SqlDataAdapter("SELECT * FROM Guardian WHERE STUDENT_NO = @student_no", ChuoDB_Connection);

select_adapt.SelectCommand.Parameters.Add("@student_no", SqlDbType.Int).Value = Convert.ToInt32(txt_bx_guardian_student_search.Text);

            select_adapt.Fill(ds);

            if (ds.Tables[0].Rows.Count == 0)
            {
                lbl_guardian_student_search.Text = "No Guardian record exists for this student. Please enter the Guardian Information";
                ChuoDB_Connection.Close();

            }

            if (ds.Tables[0].Rows.Count > 0)
            {
                lbl_guardian_student_search.Text = "";       

              while (dr.read())
                {
                    txtBox1.Text = rdr.Item["DBFieldName1"].ToString();
                    txtBox2.Text = rdr.Item["DBFieldName2"].ToString();
                }



            }                


        }
    }

Answer 1

I think you do not need DataAdapter and DataSet here. Try just with the DataReader:

string _connectionString = "Data Source=test-PC\\tester;Initial Catalog=Chuo;Integrated Security=True;Pooling=False";

string _selectCommand = @"SELECT * FROM Guardian WHERE STUDENT_NO = @student_no";

here code for the click handler:

 SqlParameter parameter = new SqlParameter("@student_no", SqlDbType.Int);
 parameter.Value = Convert.ToInt32(txt_bx_guardian_student_search.Text);

    using (IDbConnection connection = new SqlConnection(_connectionString))
            {
                connection.Open();

                using (IDbCommand command = connection.CreateCommand())
                {
                    command.Connection = connection;
                    command.CommandText = _selectCommand;
                    command.Parameters.Add("@student_no", SqlDbType.Int).Value = Convert.ToInt32(txt_bx_guardian_student_search.Text);

                    IDataReader reader = command.ExecuteReader();


                    if (reader.Read())
                    {
                        txtBox1.Text = reader["DBFieldName1"].ToString();
                        txtBox2.Text = reader["DBFieldName2"].ToString();
                    }
                    else
                    {
                        lbl_guardian_student_search.Text = "No Guardian record exists for this student. Please enter the Guardian Information";
                    }
                }
            }

Answer 2

To use a SqlDataReader you need to initialize it using the ExecuteReader method of a SqlCommand. So in your code you could discard all the part relative to the SqlDataAdapter

private void btn_guardian_student_search_Click(object sender, EventArgs e)
{
    if (rd_btn_guardian_student_no.Checked == true)
    {
        using(SqlConnection cnn = new SqlConnection(......))
        using(SqlCommand cmd = new SqlCommand(@"SELECT * FROM Guardian 
                                   WHERE STUDENT_NO = @student_no", cnn))
        {
           cnn.Open();
           cnn.Add("@student_no", SqlDbType.Int).Value = Convert.ToInt32(txt_bx_guardian_student_search.Text);
           using(SqlDataReader rd = new cmd.ExecuteReader())
           {
               if(!rd.HasRows)
                  lbl_guardian_student_search.Text = "No Guardian record exists for this student. Please enter the Guardian Information";
               else
               {
                  rdr.Read();
                  txtBox1.Text = rdr.Item["DBFieldName1"].ToString();
                  txtBox2.Text = rdr.Item["DBFieldName2"].ToString();
               }
           }                
       }
   }
}

Note that I have moved the global connection object inside the code making it a local variable that is initialized inside a using block as well the command and the reader. They are disposable objects and should be disposed when you have finished with them. The Using Statement ensure correct dispose of these objects

Also note that keeping a connection opened all the time of your application is really a big NO-NO in database server applications. You hinder the server ability to serve more requests if you keep your connection constantly open. And there is no great penalty in restoring the server connection because ADO.NET has an infrastructure called Connection Pooling that allows you to restore your connection immediately