ASP.NET Optimistic Concurrency Control

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;

namespace Concurrency
{
	/// <summary>
	/// Summary description for Product.
	/// </summary>
	public class Product : BasePage
	{
		protected System.Web.UI.WebControls.Label Label1;
		protected System.Web.UI.WebControls.Label Label2;
		protected System.Web.UI.WebControls.Label Label3;
		protected System.Web.UI.WebControls.Label Label4;
		protected System.Web.UI.WebControls.Label Label6;
		protected System.Web.UI.WebControls.Label Label7;
		protected System.Web.UI.WebControls.Label Label8;
		protected System.Web.UI.WebControls.TextBox txtName;
		protected System.Web.UI.WebControls.TextBox txtQtyPerUnit;
		protected System.Web.UI.WebControls.TextBox txtUnitPrice;
		protected System.Web.UI.WebControls.TextBox txtUnitsInStock;
		protected System.Web.UI.WebControls.TextBox txtUnitsOnOrder;
		protected System.Web.UI.WebControls.TextBox txtReorderLevel;
		protected System.Web.UI.WebControls.CheckBox chkDiscontinued;
		protected System.Web.UI.WebControls.Button btnAccept;
		protected System.Web.UI.WebControls.Button btnCancel;
		protected System.Web.UI.WebControls.DropDownList cmbCategories;
		protected System.Web.UI.WebControls.DropDownList cmbSuppliers;
		protected System.Web.UI.WebControls.Label lblConcurrencyMsg;
		protected System.Web.UI.WebControls.Label Label5;

		#region Web Form Designer generated code
		override protected void OnInit(EventArgs e)
		{
			//
			// CODEGEN: This call is required by the ASP.NET Web Form Designer.
			//
			InitializeComponent();
			base.OnInit(e);
		}
		
		/// <summary>
		/// Required method for Designer support - do not modify
		/// the contents of this method with the code editor.
		/// </summary>
		private void InitializeComponent()
		{    
			this.btnAccept.Click += new System.EventHandler(this.btnAccept_Click);
			this.btnCancel.Click += new System.EventHandler(this.btnCancel_Click);
			this.Load += new System.EventHandler(this.Page_Load);

		}
		#endregion

		#region Page Events

		private void Page_Load(object sender, System.EventArgs e)
		{
			if (! IsPostBack)
			{
				// Load the categories
				foreach (BLL.Category category in new BLL.Category().GetCategories())
					this.cmbCategories.Items.Add(new ListItem(category.Name, category.ID.ToString()));

				// Load the suppliers
				foreach (BLL.Supplier supplier in new BLL.Supplier().GetSuppliers())
					this.cmbSuppliers.Items.Add(new ListItem(supplier.Name, supplier.ID.ToString()));

				// Load the product data
				LoadProduct();
			}
		}

		/// <summary>
		/// Accepts the user changes
		/// </summary>
		private void btnAccept_Click(object sender, System.EventArgs e)
		{
			Save();
		}

		/// <summary>
		/// Cancels the product edit
		/// </summary>
		private void btnCancel_Click(object sender, System.EventArgs e)
		{
			Response.Redirect("Default.aspx");
		}

		#endregion

		/// <summary>
		/// Loads the product data based on the product ID
		/// </summary>
		private void LoadProduct()
		{
			// Get the product ID to read
			int productID = 0;
			try 
			{
				productID = Int32.Parse(Request.QueryString["ProductID"]);
			} 
			catch 
			{
				Response.Redirect("Error.aspx?msg=" + System.Web.HttpUtility.UrlEncode("The product ID is invalid."));
			}

			// Read the product's data
			BLL.Product product = new BLL.Product();
			product.ID = productID;
			if (!product.Read())
				Response.Redirect("Error.aspx?msg=" + System.Web.HttpUtility.UrlEncode("The product has been deleted by another user."));

			// Fill the form
			txtName.Text = product.Name;
			cmbCategories.Items.FindByValue(product.CategoryID.ToString()).Selected = true;
			cmbSuppliers.Items.FindByValue(product.SupplierID.ToString()).Selected = true;
			txtQtyPerUnit.Text = product.QuantityPerUnit;
			txtUnitPrice.Text = product.UnitPrice.ToString();
			txtUnitsOnOrder.Text = product.UnitsOnOrder.ToString();
			txtUnitsInStock.Text = product.UnitsInStock.ToString();
			txtReorderLevel.Text = product.ReorderLevel.ToString();
			chkDiscontinued.Checked = product.Discontinued;
			
			// Keep the original object
			SetConcurrencyObject(product);
		}
		
		/// <summary>
		/// Saves the products data
		/// </summary>
		private void Save()
		{
			// Hide the concurrency error label
			lblConcurrencyMsg.Visible = false;
			
			// Get the product ID
			int productID = Int32.Parse(Request.QueryString["ProductID"]);
			
			// Get a product instance and set the properties
			BLL.Product product = new BLL.Product(	productID,
													txtName.Text,
													Int32.Parse(cmbSuppliers.SelectedItem.Value),
													Int32.Parse(cmbCategories.SelectedItem.Value),
													txtQtyPerUnit.Text,
													decimal.Parse(txtUnitPrice.Text),
													Int32.Parse(txtUnitsInStock.Text),
													Int32.Parse(txtUnitsOnOrder.Text),
													Int32.Parse(txtReorderLevel.Text),
													chkDiscontinued.Checked
													);
			// Set the concurrency time stamp
			product.Concurrency = GetConcurrencyObject().Concurrency;
			
			try
			{
				// Update the product
				product.Update();
				
				// Redirect to the product's list
				Response.Redirect("Default.aspx");
			}
			catch (DeletedRowInaccessibleException)
			{
				Response.Redirect("Error.aspx?msg=" + System.Web.HttpUtility.UrlEncode("The product has been deleted by another user."));
			}
			catch (DBConcurrencyException)
			{
				ConcurrencyException();
			}
			catch (Exception ex)
			{
				throw ex;
			}				
		}

		/// <summary>
		/// Processes the concurrency exception
		/// </summary>
		private void ConcurrencyException()
		{
			// Get the mapping controls - object properties 
			Hashtable controls = GetControlsMap();
			
			// Update the page to show the fields that have concurrency conflicts
			ShowConcurrencyFields(controls);
			
			// Show the concurrency error label
			lblConcurrencyMsg.Visible = true;
		}

		/// <summary>
		/// Gets the controls mapped to the object's properties
		/// </summary>
		/// <returns>Control mapping</returns>
		private Hashtable GetControlsMap()
		{	
			// Map the properties to the controls
			Hashtable controls = new Hashtable();
			controls.Add("Name", this.txtName);
			controls.Add("CategoryID", this.cmbCategories);
			controls.Add("SupplierID", this.cmbSuppliers);
			controls.Add("QuantityPerUnit", this.txtQtyPerUnit);
			controls.Add("UnitPrice", this.txtUnitPrice);
			controls.Add("UnitsInStock", this.txtUnitsInStock);
			controls.Add("UnitsOnOrder", this.txtUnitsOnOrder);
			controls.Add("ReorderLevel", this.txtReorderLevel);
			controls.Add("Discontinued", this.chkDiscontinued);

			return controls;
		}

	}
}