Advanced ASPX GridView Pagination and Data Entities

#region Copyright (c) 2010 Raul Iloc
/*
{***************************************************************************}
{                                                                           }
{       Copyright (c) 2010  RAUL ILOC (rauliloc@yahoo.com)                  }
{       ALL RIGHTS RESERVED                                                 }
{                                                                           }
{   THE WORK IS PROVIDED UNDER THE TERMS OF THIS CODE PROJECT OPEN LICENSE. }
{   THE WORK IS PROTECTED BY COPYRIGHT AND/OR OTHER APPLICABLE LAW.         }
{   ANY USE OF THE WORK OTHER THAN AS AUTHORIZED UNDER THIS LICENSE         }
{   OR COPYRIGHT LAW IS PROHIBITED.                                         }
{                                                                           }
{                                                                           }
{  BY EXERCISING ANY RIGHTS TO THE WORK PROVIDED HEREIN, YOU ACCEPT AND     }
{  AGREE TO BE BOUND BY THE TERMS OF THIS LICENSE. THE AUTHOR GRANTS YOU    }
{  THE RIGHTS CONTAINED HEREIN IN CONSIDERATION OF YOUR ACCEPTANCE OF SUCH  }
{  TERMS AND CONDITIONS. IF YOU DO NOT AGREE TO ACCEPT AND BE BOUND BY THE  }
{  TERMS OF THIS LICENSE, YOU CANNOT MAKE ANY USE OF THE WORK.              }
{                                                                           }
{***************************************************************************}
*/
#endregion Copyright (c) 2010 Raul Iloc

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
//
using Ra.GridView.Util;
using Ra.GridView.Data;

namespace Ra.GridView.Web
{
    /// <summary>
    /// Defines the contact page.
    /// </summary>
    /// <remarks>
    /// This page is used to create and/or to edit a contact entity.
    /// </remarks>
    public partial class ContactPage : BaseEntityPage
    {
        /// <summary>
        /// Gets or sets the ID of the current contact entity.
        /// </summary>
        /// <remarks>
        /// Used to cache the ID of the current contact entity between postbacks!
        /// </remarks>
        private int ContactID
        {
            get
            {
                return (ViewState["ContactID"] == null ? 0 : (int)ViewState["ContactID"]);
            }
            set
            {
                ViewState["ContactID"] = value;
            }
        }

        /// <summary>
        /// Init event used to init the page with global data.
        /// </summary>
        /// <param name="sender">The sender.</param>
        /// <param name="e">The arguments.</param>
        protected void Page_Init(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                //
                // The page must not cache any data.
                //
                Response.Cache.SetCacheability(HttpCacheability.NoCache);
                //
                try
                {
                    //
                    // Clear the used cache.
                    //
                    Session["NewContactID"] = null;
                    //
                    // Init the group drop down list used as filter control.
                    //
                    List<Group> centerList = DataContext.Groups.ToList<Group>();
                    SortedDictionary<string, int> sortedData = new SortedDictionary<string, int>();
                    foreach (Group center in centerList)
                    {
                        if (!sortedData.ContainsValue(center.ID))
                            sortedData.Add(center.Name, center.ID);
                    }
                    //
                    _groupDropDownList.DataSource = sortedData;
                    _groupDropDownList.DataValueField = "value";
                    _groupDropDownList.DataTextField = "key";
                    _groupDropDownList.DataBind();
                }
                catch (Exception ex)
                {
                    RaGridViewEventLog.LogException(ex);
                    this.ErrorMessage = "Error in loading the data from the database!";
                }
            }
        }

        /// <summary>
        /// Init event used to int the page with entity data.
        /// </summary>
        /// <param name="sender">The sender.</param>
        /// <param name="e">The arguments.</param>
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                if (string.IsNullOrEmpty(ID) == false)
                {
                    int contactID = Convert.ToInt32(Request.QueryString["ID"]);
                    ViewState["ContactID"] = contactID;
                    //
                    _titleLiteral.Text = (contactID == 0 ? "New Contact" : "Edit Contact");
                    //
                    Contact contact = CreateOrLoadEntity(contactID);
                    if (contact != null)
                        InitFromEntity(contact);
                }
            }
        }

        /// <summary>
        /// Create or load an entity by its ID.
        /// </summary>
        /// <param name="contactID">The entity ID or 0 for create a new enity.</param>
        /// <returns>The entity or null for errors.</returns>
        private Contact CreateOrLoadEntity(int contactID)
        {
            Contact contact = null;
            if (contactID > 0)
            {
                try
                {
                    //
                    // Load and entity from the database.
                    //
                    contact = DataContext.Contacts.Single(item => item.ID == contactID);
                    if (contact == null)
                        throw new RaGridViewException("Contact not found!");
                }
                catch (Exception ex)
                {
                    RaGridViewEventLog.LogException(ex);
                    this.ErrorMessage = "Error in loading the entity data from the database!";
                }
            }
            else
            {
                //
                // Crete and init a new entity.
                //
                contact = new Contact();
                contact.FirstName = string.Empty;
                contact.LastName = string.Empty;
            }
            //
            return contact;
        }

        /// <summary>
        /// Init the control by using entity data.
        /// </summary>
        /// <param name="contact">The entity.</param>
        private void InitFromEntity(Contact contact)
        {
            _firstNameTextBox.Text = contact.FirstName;
            _lastNameTextBox.Text = contact.LastName;
            _phoneTextBox.Text = (contact.Phone == null ? string.Empty : contact.Phone);
            _emailTextBox.Text = (contact.Email == null ? string.Empty : contact.Email);
            _noteTextBox.Text = (contact.Note == null ? string.Empty : contact.Note);
            //
            _groupDropDownList.SelectedIndex = _groupDropDownList.Items.IndexOf(_groupDropDownList.Items.FindByValue(contact.GroupID.ToString()));
        }

        /// <summary>
        /// _saveButton Click event used to save the user inputs into the database.
        /// </summary>
        /// <param name="sender">The sender.</param>
        /// <param name="e">The arguments.</param>
        protected void _saveButton_Click(object sender, EventArgs e)
        {
            bool isNewEntity = false;
            Contact contact = CreateOrLoadEntity(this.ContactID);
            //
            if (contact != null)
            {
                try
                {
                    //
                    // Save the user inputs into the entity.
                    //
                    contact.FirstName = _firstNameTextBox.Text;
                    contact.LastName = _lastNameTextBox.Text;
                    //
                    string temp = _phoneTextBox.Text.Trim();
                    contact.Phone = (temp.Length < 1 ? null : temp);
                    //
                    temp = _emailTextBox.Text.Trim();
                    contact.Email = (temp.Length < 1 ? null : temp);
                    //
                    temp = _noteTextBox.Text.Trim();
                    contact.Note = (temp.Length < 1 ? null : temp);
                    //
                    int groupID = 0;
                    int.TryParse(_groupDropDownList.SelectedItem.Value, out groupID);
                    contact.GroupID = groupID;
                    //
                    // Save the changes into the database.
                    // 
                    if (contact.ID == 0)
                    {
                        DataContext.Contacts.AddObject(contact);
                        isNewEntity = true;
                    }
                    //
                    DataContext.SaveChanges();
                }
                catch (Exception ex)
                {
                    RaGridViewEventLog.LogException(ex);
                    this.ErrorMessage = "Error in saving the entity into the database!";
                }
            }
            //
            if (isNewEntity)
            {
                //
                // To comunicate the ID of the new created contact to the parent,
                // we must cache its value!
                //
                Session["NewContactID"] = contact.ID;
            }
            //
            // Run "OnOk()" script. Note that this will close the popup window 
            // by invoking _okPopupButton.click() event on the parent page!
            //
            ClientScript.RegisterStartupScript(this.GetType(), "contactSave", "OnOK();", true);
        }
    }
}