Advanced ASP.NET : Data-Access Components (part 2) - Using the Data-Access Component

2/6/2011 3:48:23 PM

2. Using the Data-Access Component

To use this component in a web application, you first have to make sure the appropriate connection string is configured in the web.config file, as shown here:


<add name="AdBoard" connectionString=
"Data Source=localhost\SQLEXPRESS;Initial Catalog=AdBoard;Integrated Security=SSPI" />

Next, compile and copy the component DLL file, or add a reference to it if you're using Visual Studio. The only remaining task is to add the user interface for the web page that uses the component.

To test this component, you can create a simple test page. In the example shown in Figure 2, this page allows users to browse the current listing by category and add new items. When the user first visits the page, it prompts the user to select a category.

Figure 2. The AdBoard listing

Once a category is chosen, the matching items display, and a panel of controls appears, which allows the user to add a new entry to the AdBoard under the current category, as shown in Figure 3.

Figure 3. The AdBoard listing

In order to access the component more easily, the web page imports its namespace:

Imports DatabaseComponent

The page code creates the component to retrieve information from the database and displays it by binding the DataSet to the drop-down list or GridView control:

Public Partial Class AdBoard
Inherits System.Web.UI.Page

Protected Sub Page_Load(ByVal sender As Object, _
ByVal e As System.EventArgs) Handles Me.Load

If Not Page.IsPostBack
Dim DB As New DBUtil()

lstCategories.DataSource = DB.GetCategories()
lstCategories.DataTextField = "Name"
lstCategories.DataValueField = "ID"

pnlNew.Visible = False
End If
End Sub

Protected Sub cmdDisplay_Click(ByVal sender As Object, _
ByVal e As System.EventArgs) Handles cmdDisplay.Click

Dim DB As New DBUtil()

gridItems.DataSource = DB.GetItems( _
pnlNew.Visible = True
End Sub

Protected Sub cmdAdd_Click(ByVal sender As Object, _
ByVal e As System.EventArgs) Handles cmdAdd.Click

Dim DB As New DBUtil()

DB.AddItem(txtTitle.Text, txtDescription.Text, _
Val(txtPrice.Text), Val(lstCategories.SelectedItem.Value))

gridItems.DataSource = DB.GetItems( _
Catch err As FormatException
' An error occurs if the user has entered an
' invalid price (non-numeric characters).
' In this case, take no action.
' Another option is to add a validator control
' for the price text box to prevent invalid input.
End Try
End Sub
End Class

2.1. Dissecting the Code . . .
  • Not all the functionality of the component is used in this page. For example, the page doesn't use the AddCategory() method or the version of GetItems() that doesn't require a category number. This is completely normal. Other pages may use different features from the component.

  • The code for the web page is free of data access code. It does, however, need to understand how to use a DataSet, and it needs to know specific field names to create a more attractive GridView with custom templates for layout (instead of automatically generated columns).

  • The page could be improved with error handling code or validation controls. As it is, no validation is performed to ensure that the price is numeric or even to ensure that the required values are supplied.

If you're debugging your code in Visual Studio, you'll find you can single-step from your web page code right into the code for the component, even if it isn't a part of the same solution. The appropriate source code file is loaded into your editor automatically, as long as it's available (and you've compiled the component in debug mode).

PS4 game trailer XBox One game trailer
WiiU game trailer 3ds game trailer
Top 10 Video Game
-   Minecraft Mods - MAD PACK #10 'NETHER DOOM!' with Vikkstar & Pete (Minecraft Mod - Mad Pack 2)
-   Minecraft Mods - MAD PACK #9 'KING SLIME!' with Vikkstar & Pete (Minecraft Mod - Mad Pack 2)
-   Minecraft Mods - MAD PACK #2 'LAVA LOBBERS!' with Vikkstar & Pete (Minecraft Mod - Mad Pack 2)
-   Minecraft Mods - MAD PACK #3 'OBSIDIAN LONGSWORD!' with Vikkstar & Pete (Minecraft Mod - Mad Pack 2)
-   Total War: Warhammer [PC] Demigryph Trailer
-   Minecraft | MINIONS MOVIE MOD! (Despicable Me, Minions Movie)
-   Minecraft | Crazy Craft 3.0 - Ep 3! "TITANS ATTACK"
-   Minecraft | Crazy Craft 3.0 - Ep 2! "THIEVING FROM THE CRAZIES"
-   Minecraft | MORPH HIDE AND SEEK - Minions Despicable Me Mod
-   Minecraft | Dream Craft - Star Wars Modded Survival Ep 92 "IS JOE DEAD?!"
-   Minecraft | Dream Craft - Star Wars Modded Survival Ep 93 "JEDI STRIKE BACK"
-   Minecraft | Dream Craft - Star Wars Modded Survival Ep 94 "TATOOINE PLANET DESTRUCTION"
-   Minecraft | Dream Craft - Star Wars Modded Survival Ep 95 "TATOOINE CAPTIVES"
-   Hitman [PS4/XOne/PC] Alpha Gameplay Trailer
-   Satellite Reign [PC] Release Date Trailer
Game of War | Kate Upton Commercial