ASP.NET Part 3 Instructor: Charles Moen CSCI/CINF 4230
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ASP.NETPart 3
Instructor: Charles Moen
CSCI/CINF 4230
State Management
(Continued from last week)
3
State Management
Storing the data that your web application needs
The problems• Thousands of users can be using the same web application at the same time,
so we need to be concerned about having sufficient memory and keeping track of each user’s data
• All users of your web application communicate with it over a stateless HTTP connection
Five choices• View state• Query string• Cookies• Session state• Application state
ASP.NET (MacDonald)
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Session Tracking in ASP.NET
Storing the data in a session object• Stored in memory on the server
• Tracked by the server by using a unique identifier
Scope• Global for your entire application for the current user
• Can be stored between visits by setting the Expires property
Lifetime• Times out due to inactivity after a preset amount of time, usually 20 minutes
• Lost if the user closes and restarts the browser
• May be lost if the user opens the page in another browser window
• Session.Abandon() can end the session
Typical use• Storing items in a shopping cart
ASP.NET (MacDonald)
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Session Example
Two pages that use a session for the user’s favorite color
ASP.NET (MacDonald)
<html xmlns="http://www.w3.org/1999/xhtml"><head runat="server"> <title></title></head><body> <form id="form1" runat="server"> <div> <asp:Label ID="favoriteColorLabel" runat="server" Text="Favorite color:"></asp:Label> <asp:TextBox ID="favoriteColorTextBox" runat="server"></asp:TextBox> <br /> <br /> <asp:Button ID="submitButton" runat="server" onclick="submitButton_Click" Text="Submit" /> <br /> <br /> <a href="SecondPage.aspx">SecondPage.aspx</a> </div> </form></body></html>
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Session Example
Two pages that use a session for the user’s favorite color
ASP.NET (MacDonald)
<html xmlns="http://www.w3.org/1999/xhtml"><head runat="server"> <title></title></head><body> <form id="form1" runat="server"> <div> <asp:Label ID="favoriteColorLabel" runat="server"></asp:Label> <br /> <br /> <a href="Default.aspx">Default.aspx</a> </div> </form></body></html>
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Session ExampleASP.NET (MacDonald)
public partial class _Default : System.Web.UI.Page { protected void submitButton_Click(object sender, EventArgs e) { string colorName = favoriteColorTextBox.Text; if (colorName != "") { Color favColor = new Color(colorName); Session["FavoriteColor"] = favColor; } }}
public partial class SecondPage : System.Web.UI.Page{ protected void Page_Load(object sender, EventArgs e) { Color favColor = (Color)Session["FavoriteColor"]; if (favColor != null) { favoriteColorLabel.Text = "Favorite color = " + favColor.Name; } else { favoriteColorLabel.Text = "No favorite color"; } }}
public class Color{ private string name; public string Name { get { return name; } set { name = value; } }
public Color(string name) { Name = name; }}
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C# PropertiesASP.NET (MacDonald, Mayo)
public class Color{ private string name; public string Name { get { return name; } set { name = value; } } public Color(string name) { Name = name; }}
Properties are similar to member variables in a class Easier to use and easier to code
public class Color{ private string name; public string getName() { return name; } public void setName(string value) { name = value; } public Color(string name) { this.name = name; }}
Color favColor = new Color("red");Console.WriteLine(favColor.getName());
Traditional encapsulation with a member variable Encapsulating state with a property
Color favColor = new Color("red");Console.WriteLine(favColor.Name);
Getters and setters are shorter
ADO.NET
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ADO.NET
The .NET technology for interacting with a database
• A set of classes that are part of the .NET Framework
Two models of data access
• Connected – direct data access
• Disconnected – fetch the data and store it in memory
Not the same as “data binding” in ASP.NET, which is binding a control to a data source
ASP.NET (MacDonald, Walther)
11
Three-Tier Architecture
A type of client-server architecture
ASP.NET (MacDonald, Gittleman)
PresentationTier
LogicTier
DataTier
ADO.NET
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Role of the Database
Relational database• The most common way to store data for a web application
• Organizes data into tables, and each row in a table is called a record
• Each record must have a field called the primary key, which uniquely identifies the record
• A relationship between two tables can be created by storing the primary key of one table as a foreign key in another table
• Database Management System (DBMS) is the program that organizes, stores, and manages the data, e.g. MS Access, MS SQL Server, Oracle, MySQL
Most important web sites use data stored in a database• Amazon.com – stores products, customers, orders
• Continental Airlines – stores flight schedules, reservations, frequent flyer miles
• Google – stores web page URLs, links, and keywords
• www.uhcl.edu
ASP.NET (MacDonald)
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Microsoft Access
Relational DBMS• Microsoft product
• Bundled in some versions of MS Office
• Can be used for small web applications
• Available at UHCL
The databases that we use in this class are created by MS Access
• All the tables are stored in a single file named db.mdb
• You will need to use MS Access to create the tables for your project
• The db.mdb file can be downloaded or uploaded by FTP in binary mode
• For the homework project, consider putting your db.mdb file in a directory named “App_Data” stored in your app directory inside the “pages” directory
ASP.NET
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Microsoft Access Example
Categories table• Two fields, id and category
• The primary key is “id”
ASP.NET
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Microsoft Access Example
MenuItems table• Five fields, id, item, description, price, and category
• The primary key is “id”
• The “category” field is a foreign key from Categories
ASP.NET
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SQL
SQL is used for all database interaction through ADO.NET
SQL (Structured Query Language)
• Standard language for interacting with relational databases
• Four commonly used commands
SELECT – retrieves a record
UPDATE – modifies an existing record
INSERT – adds a new record
DELETE – deletes an existing record
ASP.NET (MacDonald)
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SQL Examples
ASP.NET (MacDonald)
select id, categoryfrom Categories;
Select all the records from the Categories table
select *from MenuItemswhere category = 2;
Select only the salad records from the MenuItems table
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ADO.NET Classes
Three types of classes are used in ADO.NET
Connection
• Classes that encapsulate a connection to a database
Command
• Classes that are used to execute a command against a database
DataReader
• Classes that encapsulate the data retrieved from a database
ASP.NET (MacDonald, Walther)
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Implementations of ADO.NET Classes
The Connection, Command, and DataReader classes for particular DBMSs are separated into different namespaces
System.Data.SqlClient• MS SQL Server 7.0 or higher
System.Data.OleDb• Using an OLEDB driver; OleDbConnection, OleDbCommand, OleDbDataReader
System.Data.Odbc• Using an ODBC driver
System.Data.OracleClient• Oracle 8i or higher
ASP.NET (MacDonald, Walther)
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Direct Data Access
Steps to query the database with direct data access1. Create Connection, Command, and DataReader objects
2. Retrieve information from the database with the DataReader object and add it to a page
3. Close the connection
4. Send the page to the user agent as HTML
ASP.NET (MacDonald)
using System.Data;using System.Data.OleDb;
In your C# code, import the correct ADO.NET namespaces
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Deli Menu DemoASP.NET (MacDonald)
Use ASP.NET and Visual Studio 2008 to build a web application to display the results of a menu search by category using a DropDownList
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Demo web.configASP.NET (MacDonald)
<?xml version="1.0"?><configuration>
<connectionStrings> <add name="Deli" connectionString="Provider=Microsoft.Jet.OLEDB.4.0;Data Source=|DataDirectory|/db.mdb"/></connectionStrings>
<configuration>
Define the connection string in the web.config file so that it is available throughout your application
NOTE: This is a partial file.
Points to the App_Data folder inside your web application directory
The alias that you can use in your code
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Demo Default.aspx.csASP.NET (MacDonald)
using System;using System.Text;using System.Web;using System.Web.UI;using System.Web.UI.WebControls;using System.Data;using System.Data.OleDb;using System.Web.Configuration;
public partial class _Default : System.Web.UI.Page { private string connectionString = WebConfigurationManager.ConnectionStrings["Deli"].ConnectionString;
Use the alias defined in web.config
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Demo Page_LoadASP.NET (MacDonald)
protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { string selectSql = "SELECT id, category FROM Categories "; OleDbConnection conn = new OleDbConnection(connectionString); OleDbCommand cmd = new OleDbCommand(selectSql, conn); try { conn.Open(); OleDbDataReader reader = cmd.ExecuteReader(); while (reader.Read()) { ListItem newItem = new ListItem(); newItem.Text = reader["category"].ToString(); newItem.Value = reader["id"].ToString(); categoriesDropDownList.Items.Add(newItem); } reader.Close(); } catch (Exception error) { resultsLabel.Text = "ERROR: " + error.Message; } finally { conn.Close(); } } }
When the page loads, query the Categories table.
For each record in the results, add a list item to the DropDownList
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DemocategoriesDropDownList_SelectedIndexChanged
ASP.NET (MacDonald)
protected void categoriesDropDownList_SelectedIndexChanged(object sender, EventArgs e) { if (IsPostBack) { string selectSql = "select * from MenuItems where category = " + categoriesDropDownList.SelectedValue; OleDbConnection conn = new OleDbConnection(connectionString); OleDbCommand cmd = new OleDbCommand(selectSql, conn); OleDbDataReader reader; using (conn) { conn.Open(); reader = cmd.ExecuteReader(); StringBuilder sb = new StringBuilder(); sb.Append("<table border=\"1\" cellpadding=\"5\" width=\"640px\">"); while (reader.Read()) { sb.Append("<tr>"); sb.Append("<td width=\"100px\">"); sb.Append(reader["item"].ToString()); sb.Append("</td>"); sb.Append("<td>"); sb.Append(reader["description"].ToString()); sb.Append("</td>"); sb.Append("<td>"); sb.Append(reader["price"].ToString()); sb.Append("</td>"); sb.Append("</tr>"); } sb.Append("</table>"); resultsLabel.Text = sb.ToString(); } }}
When the DropDownList selection changes, query the MenuItems table
For each record that has a category value equal to the value of the list selection, add the record to the table as a row
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References
Ding, Wei, “ASP.NET” UHCL lecture slides, 2008.
Gittleman, Art, Computing with C# and the .NET Framework. Jones and Bartlett Publishers, 2003.
Lu, Dennis and Doug Rothaus, Microsoft (2002). “Best Practices for Using ADO.NET”. [Online]. Available: http://msdn.microsoft.com/en-us/library/ms971481.aspx
MacDonald, Matthew, Beginning ASP.NET 3.5 in C# 2008: From Novice to Professional, Second Edition. Apress, 2007.
Walther, Stephen. ASP.NET 3.5 Unleashed. SAMS, 2008.
W3Schools Online Web Tutorials. “ASP.NET”. [Online]. Available: http://www.w3schools.com/aspnet/default.asp
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