I want to create a winform that connect to a database to do things. It’s going to have to connect when it opens and then based on what the user clicks, makes queries. I’m not 100% sure what the best course is to open the connection when it loads and make that connection able to be accessed from all the different classes. I have made a test run to get the connection working that opens the DB connection when the user click the button then makes it’s query but I’d like to move the opening of the DB connection to the InitializeComponent() part and then from the components just call to the connection already made.
I have set this up so that it’s run on a case by case but is there a better way to do this? I’m I doing it that only way you can/should?
Here is the test
Form1.Designer.cs
namespace end_of_day
{
using System.Data.SqlClient;
partial class Form1
{
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.IContainer components = null;
/// <summary>
/// Clean up any resources being used.
/// </summary>
/// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
protected override void Dispose(bool disposing)
{
if (disposing && (components != null))
{
components.Dispose();
}
base.Dispose(disposing);
}
#region Windows Form Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.button1 = new System.Windows.Forms.Button();
this.label1 = new System.Windows.Forms.Label();
this.button2 = new System.Windows.Forms.Button();
this.button3 = new System.Windows.Forms.Button();
this.button4 = new System.Windows.Forms.Button();
this.SuspendLayout();
//
// button1
//
this.button1.Location = new System.Drawing.Point(78, 411);
this.button1.Name = "button1";
this.button1.Size = new System.Drawing.Size(147, 64);
this.button1.TabIndex = 0;
this.button1.Text = "Test";
this.button1.UseVisualStyleBackColor = true;
this.button1.Click += new System.EventHandler(this.button1_Click);
//
// label1
//
this.label1.AutoSize = true;
this.label1.Location = new System.Drawing.Point(13, 13);
this.label1.Name = "label1";
this.label1.Size = new System.Drawing.Size(199, 13);
this.label1.TabIndex = 1;
this.label1.Text = "ERROR: didn\'t connect to the database.";
//
// button4
//
this.button4.Location = new System.Drawing.Point(78, 201);
this.button4.Name = "button4";
this.button4.Size = new System.Drawing.Size(147, 64);
this.button4.TabIndex = 4;
this.button4.Text = "Print Out of Stock";
this.button4.UseVisualStyleBackColor = true;
this.button4.Click += new System.EventHandler(this.button4_Click);
//
// Form1
//
this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
this.ClientSize = new System.Drawing.Size(306, 523);
this.Controls.Add(this.button4);
this.Controls.Add(this.button3);
this.Controls.Add(this.button2);
this.Controls.Add(this.label1);
this.Controls.Add(this.button1);
this.Name = "Form1";
this.Text = "End of day";
this.ResumeLayout(false);
this.PerformLayout();
}
#endregion
private System.Windows.Forms.Button button1;
private System.Windows.Forms.Label label1;
private System.Windows.Forms.Button button4;
// NOTE I NEED TO BE ABLE TO CHANGE THE LABEL FROM OTHER CLASSES FIX THIS SOMEHOW
}
}
Form1.cs
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.Net.Mail;
namespace end_of_day
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
SqlConnection myConnection = queries.create_concection();
try
{
SqlDataReader myReader = null;
SqlCommand myCommand = new SqlCommand("SELECT TOP 100000 ItemName,Price,In_Stock,Vendor_Part_Num FROM Inventory",
myConnection);
myReader = myCommand.ExecuteReader();
String mess = "";
int i = 0;
while (myReader.Read())
{
if (i < 10)
{
mess += myReader["ItemName"].ToString();
mess += myReader["Price"].ToString();
mess += "\r\n";
}
i++;
}
}
catch (Exception er)
{
DialogResult dlgRes = MessageBox.Show(er.ToString(), "Error", MessageBoxButtons.YesNoCancel, MessageBoxIcon.Question);
}
}
private void button4_Click(object sender, EventArgs e)
{
SqlConnection myConnection = queries.create_concection();
DialogResult dlgRes = MessageBox.Show("Exculde Videos?",
"Options",
MessageBoxButtons.YesNoCancel,
MessageBoxIcon.Question);
String SQL_op = "";
if (dlgRes == DialogResult.Yes)
{
SQL_op = "AND NOT Dept_ID = 'video'";
}
try
{
SqlDataReader myReader = null;
SqlCommand myCommand = new SqlCommand("SELECT TOP 100000 ItemName,Price,In_Stock,Vendor_Part_Num FROM Inventory WHERE In_Stock<1 AND NOT Dept_ID = '006' "+ SQL_op+" ORDER BY Dept_ID",
myConnection);
myReader = myCommand.ExecuteReader();
String mess = "";
int i = 0;
while (myReader.Read())
{
if (i < 10)
{
mess += myReader["ItemName"].ToString();
mess += myReader["Price"].ToString();
mess += "\r\n";
}
i++;
}
dlgRes = MessageBox.Show("Had " + i + "items including: \r\n" + mess,
"Confirm Document Close",
MessageBoxButtons.YesNoCancel,
MessageBoxIcon.Question);
}
catch (Exception er)
{
dlgRes = MessageBox.Show(er.ToString(), "Error", MessageBoxButtons.YesNoCancel, MessageBoxIcon.Question);
}
}
}
}
queries.cs
using System;
using System.Collections.Generic;
using System.Xml;
using System.Linq;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.Web;
namespace end_of_day
{
public class queries
{
public static SqlConnection create_concection()
{
Boolean hasConection =true;
SqlConnection myConnection = new SqlConnection(
"Data Source=localhost\\SQLEXPRESS;" +
"Trusted_Connection=true;" +
"Initial Catalog=TESTDB; " +
"connection timeout=30"
);
try
{
myConnection.Open();
}
catch (Exception er)
{
hasConection = false;
DialogResult dlgRes = MessageBox.Show(er.ToString(), "Error", MessageBoxButtons.YesNoCancel, MessageBoxIcon.Question);
}
if (hasConection) {
// THIS SHOULD CHANGE THE LABEL OF THE MAIN FORM
//Form1 form = new Form1();
//form.MyMessage = "made it";
}
return myConnection;
}
}
}
There is absolutely a better way. Do not open a connection when the form loads, and leave it open.
A rule of thumb you should always follow is to open a connection only when you require it, and close it as soon as you are done using it. This means in practice you don’t open it until you need to run a query, as close to the actual query execution as possible, and then you close the connection as soon as the query completes.
What you are asking about, is how to design your application, and a common answer you will get is to use an n-tier design. You should read up on multitier architectures.