Professional ASP.NET 3.5 in C# and Visual Basic Part 36 ppsx

If, for example, you wanted to include a bullet list of each product in an individual group, you would simply add anotherTemplateField, insert a BulletList control and bind it to the Pro

<asp:querystringparameter DefaultValue="0" Name="CustomerID"

QueryStringField="cid" Type="String" />

</whereparameters>

</asp:LinqDataSource>

You can add multipleWhereparameters that the control will automatically concatenate in itsWhere

property using theANDoperator You can manually change the default value of theWhereproperty if you want to have multipleWhereParametersdefined, but only use a subset, or if you want to change which parameters are used dynamically at runtime This is shown in Listing 7-12, where the LinqDataSource

control has severalWhereparameters defined, but by default is using only one

Listing 7-12: Using one of multiple defined WhereParameters

<asp:LinqDataSource ID="LinqDataSource1" runat="server"

ContextTypeName="NorthwindDataContext" TableName="Customers"

Select="new (CustomerID, ContactName, ContactTitle, Region)"

Where="Country == @Country"

OrderBy="Region, ContactTitle, ContactName">

<whereparameters>

<asp:querystringparameter DefaultValue="0" Name="CustomerID"

QueryStringField="cid" Type="String" />

<asp:querystringparameter DefaultValue="USA" Name="Country"

QueryStringField="country" Type="String" />

<asp:FormParameter DefaultValue="AZ" Name="Region"

FormField="region" Type="String" />

</whereparameters>

</asp:LinqDataSource>

In this case, although threeWhereParametersare defined, theWhereproperty uses only theCountry

parameter It would be simple to change theWhereproperty’s value at runtime to use any of the defined parameters, based perhaps on a configuration setting set by the end user

The LinqDataSource control also includes a property calledAutoGenerateWhereClause, which can sim-plify the markup created by the control When set toTrue, the property causes the control to ignore the value of theWhereproperty and automatically use each parameter specified in theWhereparameters

collection in the query’sWhereclause

Defining an OrderBy Clause

When defining anOrderByclause, by default the wizard simply creates a comma-delimited list of fields

as the value for the control’sOrderByproperty The value of theOrderByproperty is then appended to the control’s LINQ query when it is executed

The control also exposes anOrderByParameterscollection, which you can also use to specifyOrderBy

values However, in most cases using the simpleOrderByproperty will be sufficient You would need to the useOrderByparameters collection only if you need to determine the value of a variable at runtime, and then order the query results based on that value

Grouping Query Data

The LinqDataSource control also makes it easy to specify a grouping for the resultset returned by the

query In the configuration wizard, you can select the Group By field for the query Once a field is

selected, the wizard then creates a default projection based on the groupby field The projection includes

two fields by default, the first calledkey, which represents the group objects specified in theGroupBy

property, and the second calleditwhich represents the grouped objects You can also add your own

columns to the projection and execute functions against the grouped data such asAverage,Min,Max, and

Count Listing 7-13 demonstrates a very simple grouping using the LinqDataSource control

Listing 7-13: Simple Data Grouping

<asp:LinqDataSource ID="LinqDataSource1" runat="server"

ContextTypeName="NorthwindDataContext" TableName="Products"

Select="new (key as Category, it as Products,

Average(UnitPrice) as Average_UnitPrice)"

GroupBy="Category">

</asp:LinqDataSource>

You can see in this sample that the Products table has been grouped by itsCategoryproperty The

LinqDataSource control created a new projection containing thekey(aliased asCategory) andit(aliased

asProducts) fields Additionally, the custom fieldaverage_unitpricehas been added, which calculates

the average unit price of the products in each category When you execute this query and bind the results

to a GridView, a simple view of the calculated average unit price is displayed The Category and Products

are not displayed because they are complex object types, and the GridView is not capable of directly

displaying them

You can access the data in either key by using the standardASP.NET Eval()function In a GridView you

would do this by creating aTemplateField, and usingItemTemplateto insert theEvalstatement as

shown here:

<asp:TemplateField>

<ItemTemplate>

<%# Eval("Category.CategoryName") %>

</ItemTemplate>

</asp:TemplateField>

In this case,TemplateFielddisplays theCategoryNamefor each grouped category in the resultset

Accessing the grouped items is just as easy If, for example, you wanted to include a bullet list of each

product in an individual group, you would simply add anotherTemplateField, insert a BulletList control

and bind it to the Products field returned by the query, as shown next:

<asp:TemplateField>

<ItemTemplate>

<asp:BulletedList DataSource=’<%# Eval("Products") %>’

DataTextField="ProductName" runat="server" ID="BulletedList" />

</ItemTemplate>

</asp:TemplateField>

Data Concurrency

Like the SqlDataSource control, the LinqDataSource control allows for data concurrency checks when

updating or deleting data As its name implies, theStoreOriginalValuesInViewStateproperty

indi-cates whether the data source control should store the original data values in ViewState Doing this when

using LINQ to SQL as the underlying data object, allows LINQ to SQL to perform data concurrency

checking before submitting updates, or deleting data

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Storing the original data in ViewState, however, can cause the size of your Web page to grow

significantly, affecting the performance of your Web site, so you may wish to disable the storing of data

in ViewState If you do, recognize that you are now responsible for any data concurrency checking that your application requires

LinqDataSource Events

The LinqDataSource control also includes a number of useful events that you can use to react to actions taken by the control at runtime Standard before and after events for Select, Insert, Update, and Delete

actions are all exposed and allow you to add, remove, or modify parameters from the control’s various parameter collections, or even cancel the event entirely

Additionally, the post action events allow you to determine whether an exception has occurred while

attempting to execute an Insert, Update, or Delete If an exception has occurred, these events allow you

to react to those exceptions, and either mark the exception as handled, or allow it to continue to bubble

up through the application

AccessDataSource Control

Although you can use the SqlDataSource to connect to Access databases, ASP.NET also provides a special AccessDataSourcecontrol This control gives you specialized access to Access databases using the Jet

Data provider, but it still uses SQL commands to perform data retrieval because it is derived from the

SqlDataSource

Despite its relative similarity to the SqlDataSource control, the AccessDataSource control has some

specialized parts First, the control does not require you to set aConnectionStringproperty Instead,

the control uses aDataFileproperty to allow you to directly specify the Access.mdbfile you want to use for data access

A side effect of not having theConnectionStringproperty is that the AccessDataSource cannot connect

to password-protected databases If you need to access a password-protected Access database, you can

use the SqlDataSource control, which allows you to provide the username and password as part of the

connection string.

Additionally, because the AccessDataSource uses the System.Data.OleDb to perform actual data access, the order of parameters matters You need to verify that the order of the parameters in any Select, Insert, Update, or Delete parameters collection matches the order of the parameters in the SQL statement

XmlDataSource Control

TheXmlDataSourcecontrol provides you with a simple way of binding XML documents, either

in-memory or located on a physical drive The control provides you with a number of properties that make

it easy to specify an XML file containing data and an XSLT transform file for converting the source

XML into a more suitable format You can also provide an XPath query to select only a certain subset

of data

You can use the XmlDataSource control’s Configure Data Wizard, shown in Figure 7-11, to configure

the control

Listing 7-14 shows how you might consume an RSS feed from the MSDN Web site, selecting all the item nodes within it for binding to a bound list control such as the GridView

Figure 7-11

Listing 7-14: Using the XmlDataSource control to consume an RSS feed

<asp:XmlDataSource ID="XmlDataSource1" Runat="server"

DataFile="http://msdn.microsoft.com/rss.xml"

XPath="rss/channel/item"

</asp:XmlDataSource>

In addition to the declarative attributes you can use with the XmlDataSource, a number of other helpful

properties and events are available

Many times, your XML is not stored in a physical file, but rather is simply a string stored in your

appli-cation memory or possibly in a SQL database The control provides theDataproperty, which accepts a

simple string of XML to which the control can bind Note that if both theDataandDataFileproperties

are set, theDataFileproperty takes precedence over theDataproperty

Additionally, in certain scenarios, you may want to export the bound XML out of the XmlDataSource

control to other objects or even save any changes that have been made to the underlying XML if it

has been bound to a control such as a GridView The XmlDataSource control provides two methods

to accommodate this First, theGetXmlDocumentmethod allows you to export the XML by returning a

basicSystem.Xml.XmlDocumentobject that contains the XML loaded in the data source control

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Second, using the control’sSavemethod, you can persist changes made to the XmlDataSource control’s loaded XML back to disk Executing this method assumes you have provided a file path in theDataFile property

The XmlDataSource control also provides you with a number of specialized events TheTransforming

event that is raised before the XSLT transform specified in theTransformorTransformFileproperties is applied and allows you to supply custom arguments to the transform

ObjectDataSource Control

TheObjectDataSourcecontrol is one of the most interesting data source controls in the ASP.NET tool-box It gives you the power to bind data controls to middle-layer business objects that can be hard-coded

or automatically generated from programs such as Object Relational (O/R) mappers

To demonstrate how to use the ObjectDataSource control, create a class in the project that represents a

customer Listing 7-15 shows a class that you can use for this demonstration

Listing 7-15: Creating a Customer class to demonstrate the ObjectDataSource control

VB

Public Class Customer

Private _customerID As Integer

Private _companyName As String

Private _contactName As String

Private _contactTitle As String

Public Property CustomerID() As Integer

Get Return _customerID End Get

Set _customerID = value End Set

End Property

Public Property CompanyName() As Integer

Get Return _companyName End Get

Set _companyName = value End Set

End Property

Public Property ContactName() As Integer

Get Return _contactName End Get

Set _contactName = value End Set

Continued

End Property

Public Property ContactTitle() As Integer

Get Return _contactTitle End Get

Set _contactTitle = value End Set

End Property

Public Function [Select](ByVal customerID As Integer) As System.Data.DataSet

’ You would implement logic here to retreive

’ Customer data based on the customerID parameter

Dim ds As New System.Data.DataSet() ds.Tables.Add(New System.Data.DataTable()) Return ds

End Function

Public Sub Insert(ByVal c As Customer)

’ Implement Insert logic End Sub

Public Sub Update(ByVal c As Customer)

’ Implement Update logic End Sub

Public Sub Delete(ByVal c As Customer)

’ Implement Delete logic End Sub

End Class

C#

public class Customer

{

private int _customerID;

private string _companyName;

private string _contactName;

private string _contactTitle;

public int CustomerID

{

get { return _customerID;

}

set { _customerID = value;

} }

Continued

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public string CompanyName

{

get

{

return _companyName;

}

set

{

_companyName = value;

}

}

public string ContactName

{

get

{

return _contactName;

}

set

{

_contactName = value;

}

}

public string ContactTitle

{

get

{

return _contactTitle;

}

set

{

_contactTitle = value;

}

}

public Customer()

{

}

public System.Data.DataSet Select(Int32 customerId)

{

// Implement logic here to retrieve the Customer

// data based on the methods customerId parameter

System.Data.DataSet ds = new System.Data.DataSet();

ds.Tables.Add(new System.Data.DataTable());

return ds;

}

Continued

public void Insert(Customer c)

{

// Implement Insert logic }

public void Update(Customer c)

{

// Implement Update logic }

public void Delete(Customer c)

{

// Implement Delete logic }

}

To start using the ObjectDataSource, drag the control onto the designer surface Using the control’s smart

tag, load the Configuration Wizard by selecting the Configure Data Source option After the wizard

opens, it asks you to select the business object you want to use as your data source The drop-down list

shows all the classes located in theApp_Codefolder of your Web site that can be successfully compiled

In this case, you want to use theCustomerclass shown in Listing 7-8

Click the Next button, and the wizard asks you to specify which methods it should use for the CRUD

operations it can perform: SELECT, INSERT, UPDATE, and DELETE Each tab lets you select a specific

method located in your business class to perform the specific action Figure 7-12 shows that you want the

control to use a method calledSelect()to retrieve data

The methods the ObjectDataSource uses to perform CRUD operations must follow certain rules in

order for the control to understand For instance, the control’sSELECTmethod must return aDataSet,

DataReader, or a strongly typed collection Each of the control’s operation tabs explains what the control

expects of the method you specify for it to use Additionally, if a method does not conform to the rules

that specific operation expects, it is not listed in the drop-down list on that tab

Finally, if yourSELECTmethod contains parameters, the wizard lets you createSelectParametersyou

can use to provide the method parameter data

When you have completed configuring the ObjectDataSource, you should have code in your page source

like that shown in Listing 7-16

Listing 7-16: The ObjectDataSource code generated by the configuration wizard

<asp:ObjectDataSource ID="ObjectDataSource1" runat="server" DeleteMethod="Delete"

InsertMethod="Insert" SelectMethod="Select" TypeName="Customer"

UpdateMethod="Update">

<SelectParameters>

<asp:QueryStringParameter Name="customerID" QueryStringField="ID"

Type="Int32" />

</SelectParameters>

</asp:ObjectDataSource>

As you can see, the wizard has generated the attributes for theSELECT,UPDATE,INSERT, andDELETE

methods you specified in the wizard Also notice that it has added theSelectparameter Depending

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on your application, you could change this to any of theParameterobjects discussed earlier, such as a

ControlParameterorQuerystringParameterobject

Figure 7-12

ObjectDataSource Events

The ObjectDataSource control exposes several useful events that you can hook into First, it includes

events that are raised before and after the control performs any of the CRUD actions, such as selecting or deleting events

It also includes pre- and post-events that are raised when the object that is serving as the data source

is created or disposed of, as well as when an event that is raised before a filter is applied to the data

All these events give you great power when you must react to the different ways the ObjectDataSource control behaves

SiteMapDataSource Control

TheSiteMapDataSourceenables you to work with data stored in your Web site’s SiteMap configuration

file if you have one This can be useful if you are changing your site map data at runtime, perhaps based

on user privilege or status

Note two items regarding the SiteMapDataSource control First, it does not support any of the data

caching options that exist in the other data source controls provided (covered in the next section), so

you cannot natively cache your sitemap data Second, the SiteMapDataSource control does not have any

configuration wizards like the other data source controls This is because the SiteMap control can be

bound only to the SiteMap configuration data file of your Web site, so no other configuration is possible

Listing 7-17 shows an example of using the SiteMap control

Listing 7-17: Using the SiteMapDataSource control

<asp:SiteMapDataSource ID="SiteMapDataSource1" Runat="server" />

Using the SiteMapDataSource control is discussed in greater detail in Chapter 14

Configuring Data Source Control Caching

Caching is built into all the data source controls that ship with ASP.NET except the SiteMapDataSource

control This means that you can easily configure and control data caching using the same declarative

syn-tax All data source controls (except the SiteMapDataSource control) enable you to create basic caching

policies including a cache direction, expiration policies, and key dependencies

Remember that the SqlDataSource control’s caching features are available only if you have set the

DataSourceModeproperty toDataSet If it is set toDataReader, the control throws a

NotSupport-edException.

Cache duration can be set to a specific length of time, such as 3600 seconds (60 minutes), or you can set it

toInfiniteto force the cached data to never expire Listing 7-18 shows how you can easily add caching

features to a data source control

Listing 7-18: Enabling caching on a SqlDataSource control

<asp:SqlDataSource ID="SqlDataSource1" Runat="server"

SelectCommand="SELECT * FROM [Customers]"

ConnectionString="<%$ ConnectionStrings:AppConnectionString1 %>"

DataSourceMode="DataSet"

ConflictDetection="CompareAllValues"

EnableCaching="True" CacheKeyDependency="SomeKey" CacheDuration="Infinite">

<SelectParameters>

<asp:QueryStringParameter Name="CustomerID"

QueryStringField="id" Type="String"></asp:QueryStringParameter>

</SelectParameters>

</asp:SqlDataSource>

Some controls also extend this core set of caching features with additional caching functionality

specific to their data sources For instance, if you are using the SqlDataSource control, you can use the

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