the data source_controls

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The Data Source

Object Model


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Introduction-1

The key issue with ASP.NET data

binding is a lack of a higher-level and

possibly declarative model for datafetching and manipulation (edit, insert,

and delete). As a result, an ASP.NET

1.x data access layer is boring to writeand requires hundreds of lines of code

even for relatively simple scenarios.


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Introduction-2

The ASP.NET 2.0 data source model

addresses this problem. To simplify the

data binding mechanism, thearchitecture of data-bound controls now

supports a new family of data

componentsthe data sourcecomponentswhich in turn support a

declarative model of binding.


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Introduction-3

The data source control represents a

source of data that returns and accepts

data over a well-known stream suchas SQL, XML, DataSet, and custom

formats such as the Microsoft Excel

worksheets.


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The Rationale of Data Source

Components The data binding model of ASP.NET 2.0

provides two ways of connecting

programmatically (as in ASP.NET 1.x)and declaratively (using data source

components)


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Codeless Data Binding

In ASP.NET 2.0 developers can set up

sophisticated Web sites without knowing a lot

of SQL or the page life cycle. Codeless data

binding, and the data source model in

particular, also lets developers work together,

each contributing the best of his skills.

ASP.NET 2.0 data binding enables pagedevelopers to implement data binding

scenarios, including displaying, editing,

paging, and sorting data, with no code.


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ASP.NET 2.0 adds a new property to all

data-bound controls so that any control

can be successfully bound to a newdata source control. The new

property,DataSourceId, matches the

name of a data source control defined inthe same page.

The following code snippet shows how

to list the employees in the NorthwindEmployees database. The data-bound

control used for the output is the

Repeater.


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Defining a Standard Set of Data

Operations A data source component is a data control

that can implement some or all of a standard

set of data operations. Whether a controlimplements the entire standard set of

operations or only a subset depends on the

class.

The standard set of data operations includesthe four basic I/O operations: select, delete,

insert, and update.


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Binding Data Source Components

to Controls One difference between data source

components and ASP.NET 1.x bindable

classes is that the new data sourceobject model allows you to select,insert, delete, and update data stored ina bound sourcebe it a relationaldatabase,an XML file, or an Exceldocument.


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Data Source Control Internals

A data source control is a .NET

Framework class that facilitates the

binding ofdata between data stores anddata-bound controlsboth existing

controls such as the DataGridand new

data-bound controls such as GridView,TreeView, and DetailsView.


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The DataSourceControlabstract classserves as the base class for all datasource controls and defines theinterface between data-bound controlsand the underlying data.

A data source control exposes thecontents of its underlying data sourcethrough a set of properties andmethods. Some of these members arespecific to the control; others arecommon to all source controls and aredefined as part of the IDataSource

interface.


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Tabular Data Source Controls

shows a diagram of the classes that form the datasource object model.


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Tabular data source controls areAccessDataSource,

DataSetDataSource,

Object-DataSource, and SqlDataSource.


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SqlDataSource control

The SqlDataSource control is a data

source control that represents a

connection to a relational data storesuch as SQL Server or Oracle or any

data source accessible through OLE DB

and ODBC bridges.


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You set up the connection to the data store

using two main properties,ConnectionStringand ProviderName. The former representsthe connection string and contains enoughinformation to open a session with theunderlying engine. The latter specifies thenamespace of the ADO.NET managedprovider to use for the operation. TheProviderName property defaultsSystem.Data.SqlClient, which means that the

default data store is SQL Server.


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Continue..

The DataSourceMode property controls

how the Select command retrieves data.

The DataSourceMode property acceptsvalues defined by the

SqlDataSourceMode enumeration

DataSetand DataReader.


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Code Usage


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The AccessDataSourceClass

TheAccessDataSource control is a data source control thatrepresents a connection

to an Access database.

In particular, theAccessDataSource control replacesproperties such as ConnectionStringand

ProviderName with a more directDataFileproperty. Youset this property to the .mdb database file of choice. The

data source control resolves the file path at run time anduses the Microsoft Jet 4 OLE DB provider to connect tothe database.


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Code Usage

The following code shows how to use theAccessDataSource control to open an .mdb fileand bind its content to a drop-down list control.


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Several features of theAccessDataSource control

are inherited from the base class, SqlDataSource.In fact, the Access data source control is basically

a SQL data source control optimized to work with

Access databases.

The ShareModeproperty controls how the Access

data source opens thedatabase and determines

what data operations can be performed. The

defaultvalue isRead, which means that only theSelectoperation can be accomplished


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In read mode, the CanDelete, CanInsert, and

CanUpdateproperties all returnfalse, thusblocking the corresponding data operations. To

enable read/write operations, set ShareMode to

ReadWrite.


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The DataSetDataSourceClass

TheDataSetDataSource class takes an XML fileor static data (such as an XML string) as input andexposes theDataSetrepresentation of this data to

databound controls.

TheDataSetDataSource class instantiates aDataSetobject and uses theDataSetobjectsReadXmlmethod to parse the XML input. Ideally,the supplied XML data is a DiffGram script or anyXML file created by theDataSets WriteXmlmethod.


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Code Usage


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The ObjectDataSourceClass

The ObjectDataSource class enables businesscomponents to associate their contents to data-

bound controls. The class supports declarative

parameters that allow developers to pass page-

level variables to the objects methods.

The ObjectDataSource control is designed to

simplify and encourage a common practice among

page developersencapsulating data retrieval and business logic into an additional layer between the

presentation page and data provider.


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The SiteMapDataSourceClass

A site map is a graph that represents all the pagesand directories found in a Web site.

Site map information is used to show users the

logical coordinates of the page they arevisiting,allow them to access site locationsdynamically, and render all the navigationinformation in a graphical fashion. The site map isa hierarchical piece of information that can beused as input for a hierarchical data sourcecontrol. This control is the SiteMapDataSourceclass.


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ASP.NET 2.0 provides richer support for

site maps. You start by creating a

configuration file named app.sitemap in theroot of the Web application. The file

describes the relationship between pages on

the site.


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The XmlDataSourceClass

TheXmlDataSource control is a special

type of data source control that supports

both tabular and hierarchical views of data.The tabular view of XML data is just a list

of nodes at a given level of hierarchy,

whereas the hierarchical view shows thecomplete hierarchy.


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An XML node is an instance of the

XmlNode class; the complete hierarchy is an

instance of theXmlDocumentclass. The

XML data source supports both read-only

and read-write scenarios.

TheXmlDataSource control can accept

XML input data as a relative or absolute

filename assigned to theDataFileproperty

or as a string containing the XML content

assigned to theDataproperty.


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The control exposes that data through the

IDataSource or theIHierarchicalDataSource

interface. In

general, theXmlDataSource control is commonly

bound to a hierarchical control, such as theTreeView.


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Code Usdage(1)

To understand how the XML data source works, consider

the following small XML file, named data.xml:


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Code Usage(2)


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The Final Result


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Using the SqlDataSourceControl

The SqlDataSource control represents a

connection to an ADO.NET managed dataprovider, such as SQL Server, OLEDB,

ODBC, Oracle, or a third-party provider.


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Data Source Parameters

In the programming interface of theSqlDataSource control each command propertyhas its own collection of parameters. A parametercollection is a collection class named

ParameterCollection. It stores objects whose base class isParameter. TheParameterclass representsa parameter in a parameterized query, filterexpression, or command executed by a datasource control.


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Code Usage(1)

@MinID">


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The query contains a placeholder named

@MinID. The data source control

automatically populates the placeholderwith the information returned by the

ControlParameterobjectone of the

supported parameter types in ASP.NET2.0. The


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Parameter Types

How a parameter is bound to a value

depends on the type of the parameter.


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Parameter Types in ASP.NET 2.0

Parameter Description

ControlParameter: Gets the parameter value

from any public property of a server control.

CookieParameter: Sets the parameter valuebased on the content of the specified HTTP

cookie.

FormParameter: Gets the parameter valuefrom the specified input field in the HTTP

request form.


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ProfileParameter: Gets the parameter value from

the specified property name in the profile object created from the applications

personalization scheme.

QueryStringParameter: Gets the parametervalue from the specified variable in the

request query string.

SessionParameter: Sets the parameter value

based on the content of the specified

Session slot.


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Each parameter class has aNameproperty

and a set of properties specific to its role

and implementation.


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Caching Behavior

Data caching is crucial to any realistic Webapplication and an important feature tooptimize to make the application run faster.

Caching is also an important aspect of datasource controls. A data source controlretrieves data that will be made available toother components within the application.

When multiple pages need to access thisinformation, an up-to-date cache providesfor a significantly faster response.


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You can instruct the SqlDataSource controlto cache the results of a query for a certain

amount of timebut only if the data source

mode isDataSet.

The Sql-DataSource control provides

automatic caching using a time-based cache

expiration policy. It can also support an

expiration policy based on the new

SqlCacheDependency component.


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Enabling Automatic Caching

To enable caching on the data sourcecaching isdisabled by defaultyou set theEnableCaching

property to true. You should also give the

CacheDurationproperty a nonzero value.

The CacheDurationproperty specifies the

number of seconds before the contents of

the data source are discarded, to be reloaded

on the next request.


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Code


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SQL Server Cache Dependency

The SqlDataSource control also supports a form of cache

expiration based on a dependency between its contents and

a table in a SQL Server database.

The dependency is specified as a string property. The

syntax has the form database:table. The database part ofthe string must refer to a database

listed under the section of the

web.config file,and the table part must be the name of a

table in that database. You canspecify multiple table dependencies by separating them

with semicolons


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Code


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