ASP.NET 4 Unleased - p 87 pptx

After you register the control, you can simply declare the MovieDataSource control in the page to represent the contents of the Movies database table.. Creating Custom Parameter Objects

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LISTING 18.41 ShowMovieDataSource.aspx

<%@ Page Language=”C#” %>

<%@ Register TagPrefix=”custom” Namespace=”AspNetUnleashed.Samples” %>

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.1//EN”

“http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd”>

<title>Show Movie DataSource</title>

</head>

<body>

<div>

<asp:GridView

id=”grdMovies”

DataSourceID=”srcMovies”

Runat=”server” />

<custom:MovieDataSource

id=”srcMovies”

FIGURE 18.11 Using the MovieDataSource control to display movies

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</div>

</form>

</body>

</html>

The custom control must be registered with a <%@ Register %> directive at the top of

Listing 18.41 After you register the control, you can simply declare the MovieDataSource

control in the page to represent the contents of the Movies database table

NOTE

As an alternative to registering the MovieDataSource control in a page, you can

regis-ter the control for an entire application in the web configuration file within the

<pages> element

Creating Custom Parameter Objects

The standard DataSource Parameter objects included in the ASP.NET Framework enable

you to represent objects such as query string values, items from Session state, and the

values of control properties If none of the standard Parameter objects satisfy your

require-ments, you always have the option of creating a custom Parameter object

You create a custom Parameter object by deriving a new class from the base Parameter

class In this section, we create two custom parameters The first is a UsernameParameter

that automatically represents the current username Next is a PagePropertyParameter that

represents the current value of a property contained in the page

Creating a Username Parameter

The UsernameParameter class is contained in Listing 18.42 The class in Listing 18.42

derives from the Parameter class and overrides the Evaluate() method of the base class

The Evaluate() method determines what the parameter represents

LISTING 18.42 UsernameParameter.cs

using System;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

namespace MyControls

{

public class UsernameParameter : Parameter

{

protected override object Evaluate(HttpContext context, Control control)

{

if (context != null)

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return context.User.Identity.Name;

else

return null;

}

The UsernameParameter returns the current username The parameter retrieves this

infor-mation from the current HttpContext passed to the Evaluate() method The

UsernameParameter is used in the page in Listing 18.43

LISTING 18.43 ShowUsernameParameter.aspx

<%@ Register TagPrefix=”custom” Namespace=”MyControls” %>

.guestbook td,.guestbook th

{

padding:5px;

font:14px Arial,Sans-Serif;

}

</style>

<title>Show Username Parameter</title>

</head>

<body>

<div>

<asp:FormView

id=”frmGuestbook”

DataSourceID=”srcGuestbook”

DefaultMode=”Insert”

Runat=”server”>

<asp:Label

ID=”lblComment”

Text=”Comment:”

AssociatedControlID=”txtComment”

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<br />

<asp:TextBox

id=”txtComment”

Text=’<%# Bind(“comment”) %>’

TextMode=”MultiLine”

Columns=”50”

Rows=”4”

<br />

<asp:Button

id=”btnInsert”

Text=”Add Entry”

CommandName=”Insert”

</InsertItemTemplate>

</asp:FormView>

<hr />

<asp:GridView

id=”grdGuestbook”

CssClass=”guestbook”

<asp:ObjectDataSource

id=”srcGuestbook”

TypeName=”GuestbookComponent”

SelectMethod=”GetEntries”

InsertMethod=”AddEntry”

Runat=”server”>

<custom:UsernameParameter name=”username” />

</InsertParameters>

</asp:ObjectDataSource>

</div>

</form>

</body>

</html>

The UsernameParameter is declared in the ObjectDataSource control’s InsertParameters

collection When you add a new entry to the guestbook, your username is added

automat-ically (see Figure 18.12)

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Creating a Page Property Parameter

PagePropertyParameter enables you to represent an arbitrary property of the current page

The property being represented can return whatever type of value you want The code for

the PagePropertyParameter is contained in Listing 18.44

LISTING 18.44 PagePropertyParameter.cs

using System;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

namespace MyControls

{

public class PagePropertyParameter : Parameter

{

private string _propertyName;

protected override object Evaluate(HttpContext context, Control control)

{

return DataBinder.Eval(control.Page, PropertyName);

}

FIGURE 18.12 Inserting records with the UsernameParameter

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public string PropertyName

{

get { return _propertyName; }

set { _propertyName = value; }

}

The component in Listing 18.44 overrides the Evaluate method of the base Parameter

class The DataBinder.Eval() method is used to return the value of a property of the

current page

The page in Listing 18.45 uses the PagePropertyParameter to represent a property of the

page named CurrentUsername This property returns the current username

LISTING 18.45 ShowPagePropertyParameter.aspx

<%@ Register TagPrefix=”custom” Namespace=”MyControls” %>

Public ReadOnly Property CurrentUsername() As String

Get

Return User.Identity.Name

End Get

End Property

</script>

.guestbook td,.guestbook th

{

padding:5px;

font:14px Arial,Sans-Serif;

}

</style>

<title>Show Page Property Parameter</title>

</head>

<body>

<div>

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<asp:FormView

id=”frmGuestbook”

DefaultMode=”Insert”

Runat=”server”>

<asp:Label

ID=”lblComment”

Text=”Comment:”

AssociatedControlID=”txtComment”

<br />

<asp:TextBox

id=”txtComment”

Text=’<%# Bind(“comment”) %>’

TextMode=”MultiLine”

Columns=”50”

Rows=”4”

<br />

<asp:Button

id=”btnInsert”

Text=”Add Entry”

CommandName=”Insert”

</InsertItemTemplate>

</asp:FormView>

<hr />

<asp:GridView

id=”grdGuestbook”

CssClass=”guestbook”

<asp:ObjectDataSource

id=”srcGuestbook”

TypeName=”GuestbookComponent”

SelectMethod=”GetEntries”

InsertMethod=”AddEntry”

Runat=”server”>

<custom:PagePropertyParameter

Name=”Username”

PropertyName=”CurrentUsername” />

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</InsertParameters>

</asp:ObjectDataSource>

</div>

</form>

</body>

</html>

In Listing 18.45, the PagePropertyParameter represents the current username Because the

PagePropertyParameter can represent any page property, the parameter could represent

any type of value

Summary

In this chapter, you learned how to use the ObjectDataSource control to represent

differ-ent types of objects In the first section, you were provided with sample code that

demon-strated how you can use the ObjectDataSource control to represent a collection,

DataReader, DataSet, a LINQ to SQL query, and a web service

We also discussed how you can use the ObjectDataSource control to page, sort, and filter

data You learned how to implement both user interface paging and data source paging,

which enables you to efficiently work with very large sets of records

Next, we examined how you can handle ObjectDataSource control events You learned

how to add and modify the parameters represented by the ObjectDataSource control You

also learned how to gracefully handle errors raised when executing an ObjectDataSource

control method

Finally, we discussed two methods of extending the ObjectDataSource control You

learned how to derive a new control from the base ObjectDataSource control to represent

specialized data sources such as a Product data source We also discussed how you can

create custom Parameter objects that can be used with the ObjectDataSource control

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ptg

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Building Data Access

Components with

ADO.NET

Connected Data Access Disconnected Data Access Executing Asynchronous Database Commands Building Database Objects with the NET Framework

Summary

In the previous chapter, you learned how to use the

ObjectDataSource control to bind data controls—such as

the GridView or DetailsView controls—to a data access

component In this chapter, we shift focus from the

ObjectDataSource control to the topic of building data

access components

This chapter provides you with an overview of ADO.NET,

which is the main set of classes included in NET

Framework for working with database data For example,

under the covers, the SqlDataSource control uses ADO.NET

classes to retrieve data from a SQL Server database

The classes in ADO.NET Framework support two models of

data access: a connected and disconnected model In the

first part, you learn how to take advantage of the connected

model of data access You learn how to use ADO.NET

Connection, Command, and DataReader classes to retrieve and

modify database data

In the next part, you learn how to take advantage of the

disconnected model of data access represented by ADO.NET

DataAdapter, DataTable, DataView, and DataSet classes You

can use these classes to build an in-memory representation

of database data

Finally, at the end of this chapter, we explore two advanced

topics You learn how to take advantage of two important

new features included in ADO.NET 2.0 First, you learn how

to improve the performance of your database access code by

executing asynchronous database commands You learn how

to build asynchronous ASP.NET pages that execute

asynchro-nous ADO.NET commands

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