Professional ASP.NET 3.5 in C# and Visual Basic Part 43 pps

If you are having trouble getting permissions to work with the database, make a data connection to the file from the Visual Studio Server Explorer by right-clicking on the Data Connectio

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Evjen c07.tex V2 - 01/28/2008 2:01pm Page 375

Chapter 7: Data Binding in ASP.NET 3.5 Summar y

In this chapter, you examined data binding in ASP.NET The introduction of data source controls such as the LinqDataSource control, SqlDataSource control, or the XmlDataSource control makes querying and

displaying data from any number of data sources an almost trivial task Using the data source controls’ own wizards, you learned how easy it is to generate powerful data access functionality with almost no

code required

You examined how even a beginning developer can easily combine the data source controls with the

GridView, ListView, and DetailsView controls to create powerful data manipulation applications with a minimal amount of coding

You saw how ASP.NET includes a multitude of controls that can be data-bound, specifically examining how, since ASP.NET 1.0/1.1, many controls have been enhanced, and examining the features of the data bound controls that are included in the ASP.NET toolbox, such as the GridView, TreeView, ListView,

and Menu controls, the new FormView control

Finally, you looked at how the inline data-binding syntax has been improved and strengthened with the addition of the XML-specific data-binding expressions

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Data Management

with ADO.NET

This chapter provides information on programming with the data management features that are

part of ADO.NET, a key component of the NET Framework and of your ASP.NET development

The discussion begins with the basics of ADO.NET and later dives into the ways you can use various

features that make up ADO.NET to manage data contained in a relational database

ADO.NET, first introduced in version 1.0 of the NET Framework, provided an extensive array of

features to handle live data in a connected mode or data that is disconnected from its underlying

data store ADO.NET 1.0 was primarily developed to address two specific problems in getting

at data The first had to do with the user’s need to access data once and to iterate through a

collection of data in a single instance This need often arose in Web application development

ADO.NET addresses a couple of the most common data-access strategies that are used for

applica-tions today When classic ADO was developed, many applicaapplica-tions could be connected to the data

store almost indefinitely Today, with the explosion of the Internet as the means of data

communi-cation, a new data technology is required to make data accessible and updateable in a disconnected

architecture

The first of these common data-access scenarios is one in which a user must locate a collection of

data and iterate through this data a single time This is a popular scenario for Web pages When a

request for data from a Web page that you have created is received, you can simply fill a table with

data from a data store In this case, you go to the data store, grab the data that you want, send

the data across the wire, and then populate the table In this scenario, the goal is to get the data in

place as fast as possible

The second way to work with data in this disconnected architecture is to grab a collection of data

and use this data separately from the data store itself This could be on the server or even on the

client Although the data is disconnected, you want the ability to keep the data (with all of its tables

and relations in place) on the client side Classic ADO data was represented by a single table that

you could iterate through ADO.NET, however, can be a reflection of the data store itself, with tables,

columns, rows, and relations all in place When you are done with the client-side copy of the data,

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Chapter 8: Data Management with ADO.NET

you can persist the changes that you made in the local copy of data directly back into the data store

The technology that gives you this capability is the DataSet, which will be covered shortly

Although classic ADO was geared for a two-tiered environment (client-server), ADO.NET addresses a

multi-tiered environment ADO.NET is easy to work with because it has a unified programming model

This unified programming model makes working with data on the server the same as working with data

on the client Because the models are the same, you find yourself more productive when working with

ADO.NET

Basic ADO.NET Features

This chapter begins with a quick look at the basics of ADO.NET and then provides an overview of basic

ADO.NET capabilities, namespaces, and classes It also reviews how to work with the

Connection,Command,DataAdapter,DataSet, andDataReaderobjects

Common ADO.NET Tasks

Before jumping into the depths of ADO.NET, step back and make sure that you understand some of the

common tasks you might perform programmatically within ADO.NET This next section looks

at the process of selecting, inserting, updating, and deleting data

The following example makes use of theNorthwind.mdfSQL Server Express Database file To get this

database, please search for ‘‘Northwind and pubs Sample Databases for SQL Server 2000’’ You can find

this link at

www.microsoft.com/downloads/details.aspx?familyid=06616212-0356-46a0-8da2-eebc53a68034&displaylang=en Once installed, you will find the Northwind.mdf file in the

C:\ SQL Server 2000 Sample Databases directory To add this database to your ASP.NET application,

create anApp_Datafolder within your project (if it isn’t already there) and right-click on the folder and

select Add Existing Item From the provided dialog box, you are then able to browse to the location of the

Northwind.mdffile that you just installed If you are having trouble getting permissions to work with

the database, make a data connection to the file from the Visual Studio Server Explorer by right-clicking

on the Data Connections node and selecting Add New Connection from the provided menu You will be

asked to be made the appropriate user of the database ThenVS will make the appropriate changes on your

behalf for this to occur.

Selecting Data

After the connection to the data source is open and ready to use, you probably want to read the data from

the data source If you do not want to manipulate the data, but simply to read it or transfer it from one

spot to another, you use theDataReaderclass

In the following example (Listing 8-1), you use theGetCompanyNameData()function to provide a list of

company names from the SQL Northwind database

Listing 8-1: Reading the data from a SQL database using the DataReader class

VB

Imports Microsoft.VisualBasic

Imports System.Collections.Generic

Continued

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Imports System.Data

Imports System.Data.SqlClient

Public Class SelectingData

Public Function GetCompanyNameData() As List(Of String)

Dim conn As SqlConnection

Dim cmd As SqlCommand

Dim cmdString As String = "Select CompanyName from Customers"

conn = New SqlConnection("Data Source=.\SQLEXPRESS;AttachDbFilename=

|DataDirectory|\NORTHWND.MDF;Integrated Security=True;

User Instance=True") ’ Put this string on one line in your code

cmd = New SqlCommand(cmdString, conn)

conn.Open()

Dim myReader As SqlDataReader

Dim returnData As List(Of String) = New List(Of String)

myReader = cmd.ExecuteReader(CommandBehavior.CloseConnection)

While myReader.Read()

returnData.Add(myReader("CompanyName").ToString())

End While

Return returnData

End Function

End Class

C#

using System.Data;

using System.Data.SqlClient;

using System.Collections.Generic;

public class SelectingData

{

public List<string> GetCompanyNameData()

{

SqlConnection conn;

SqlCommand cmd;

string cmdString = "Select CompanyName from Customers";

conn = new

SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=

User Instance=True"); // Put this string on one line in your code cmd = new SqlCommand(cmdString, conn);

conn.Open();

SqlDataReader myReader;

List<string> returnData = new List<string>();

myReader = cmd.ExecuteReader(CommandBehavior.CloseConnection);

while (myReader.Read())

{

returnData.Add(myReader["CompanyName"].ToString());

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} return returnData;

}

In this example, you create an instance of both theSqlConnectionand theSqlCommandclasses Then,

before you open the connection, you simply pass theSqlCommandclass a SQL command selecting specific

data from the Northwind database After your connection is opened (based upon the commands passed

in), you create aDataReader To read the data from the database, you iterate through the data with

theDataReaderby using themyReader.Read()method After theList(Of String)object is built, the

connection is closed, and the object is returned from the function

Inserting Data

When working with data, you often insert the data into the data source Listing 8-2 shows you how to do

this This data may have been passed to you by the end user through the XML Web Service, or it may be

data that you generated within the logic of your class

Listing 8-2: Inserting data into SQL Server

VB

Public Sub InsertData()

Dim cmdString As String = "Insert Customers (CustomerID, _

CompanyName, ContactName) Values (’BILLE’, ’XYZ Company’, ’Bill Evjen’)"

User Instance=True") ’ Put this string on one line in your code cmd = New SqlCommand(cmdString, conn)

conn.Open()

cmd.ExecuteNonQuery()

conn.Close()

End Sub

C#

public void InsertData()

{

SqlConnection conn;

SqlCommand cmd;

string cmdString = "Insert Customers (CustomerID, CompanyName,

ContactName) Values (’BILLE’, ’XYZ Company’, ’Bill Evjen’)";

conn = new

conn.Open();

cmd.ExecuteNonQuery();

conn.Close();

}

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Inserting data into SQL is pretty straightforward and simple Using the SQL command string, you

insert specific values for specific columns The actual insertion is initiated using the

cmd.Execute-NonQuery()command This executes a command on the data when you don’t want anything

in return

Updating Data

In addition to inserting new records into a database, you frequently update existing rows of data

in a table Imagine a table in which you can update multiple records at once In the example in

Listing 8-3, you want to update an employee table by putting a particular value in theemp_bonuscolumn

if the employee has been at the company for five years or longer

Listing 8-3: Updating data in SQL Server

VB

Public Function UpdateEmployeeBonus() As Integer

Dim RecordsAffected as Integer

Dim cmdString As String = "UPDATE Employees SET emp_bonus=1000 WHERE " & _

"yrs_duty>=5"

conn.Open()

RecordsAffected = cmd.ExecuteNonQuery()

conn.Close()

Return RecordsAffected

End Function

C#

public int UpdateEmployeeBonus()

{

SqlConnection conn;

SqlCommand cmd;

int RecordsAffected;

string cmdString = "UPDATE Employees SET emp_bonus=1000 WHERE yrs_duty>=5";

conn = new

conn.Open();

RecordsAffected = cmd.ExecuteNonQuery();

conn.Close();

return RecordsAffected;

}

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This update function iterates through all the employees in the table and changes the value of the

emp_bonus field to1000if an employee has been with the company for more than five years This is

done with the SQL command string The great thing about these update capabilities is that you can

capture the number of records that were updated by assigning theExecuteNonQuery()command to the

RecordsAffectedvariable The total number of affected records is then returned by the function

Deleting Data

Along with reading, inserting, and updating data, you sometimes need to delete data from the data

source Deleting data is a simple process of using the SQL command string and then the

ExecuteNon-Query()command as you did in the update example See Listing 8-4 for an illustration of this

Listing 8-4: Deleting data from SQL Server

VB

Public Function DeleteEmployee() As Integer

Dim RecordsAffected as Integer

Dim cmdString As String = "DELETE Employees WHERE LastName=’Evjen’"

conn.Open()

RecordsAffected = cmd.ExecuteNonQuery()

conn.Close()

Return RecordsAffected

End Function

C#

public int DeleteEmployee()

{

SqlConnection conn;

SqlCommand cmd;

int RecordsAffected;

string cmdString = "DELETE Employees WHERE LastName=’Evjen’";

conn = new

conn.Open();

RecordsAffected = cmd.ExecuteNonQuery();

conn.Close();

return RecordsAffected;

}

You can assign theExecuteNonQuery()command to anIntegervariable (just as you did for the update

function) to return the number of records deleted

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Basic ADO.NET Namespaces and Classes

The six core ADO.NET namespaces are shown in the following table In addition to these namespaces,

each new data provider can have its own namespace As an example, the Oracle NET data provider adds

a namespace ofSystem.Data.OracleClient(for the Microsoft-built Oracle data provider)

Namespace Description

System.Data This namespace is the core of ADO.NET It contains classes used by all

data providers It contains classes to represent tables, columns, rows, and theDataSetclass It also contains several useful interfaces, such as

IDbCommand,IDbConnection, andIDbDataAdapter These interfaces are used by all managed providers, enabling them to plug into the core of ADO.NET

System.Data.Common This namespace defines common classes that are used as base classes for

data providers All data providers share these classes A few examples areDbConnectionandDbDataAdapter

System.Data.OleDb This namespace defines classes that work with OLE-DB data sources

using the NET OleDb data provider It contains classes such as

OleDbConnectionandOleDbCommand

System.Data.Odbc This namespace defines classes that work with the ODBC data sources

using the NET ODBC data provider It contains classes such as

OdbcConnectionandOdbcCommand

System.Data.SqlClient This namespace defines a data provider for the SQL Server 7.0 or higher

database It contains classes such asSqlConnectionandSqlCommand

System.Data.SqlTypes This namespace defines a few classes that represent specific data types

for the SQL Server database

ADO.NET has three distinct types of classes commonly referred to asDisconnected,Shared, andData

Providers TheDisconnectedclasses provide the basic structure for the ADO.NET framework A good example of this type of class is theDataTableclass The objects of this class are capable of storing data

without any dependency on a specific data provider TheSharedclasses form the base classes for data

providers and are shared among all data providers TheData Providerclasses are meant to work with different kinds of data sources They are used to perform all data-management operations on specific

databases TheSqlClientdata provider, for example, works only with the SQL Server database

A data provider containsConnection,Command,DataAdapter, andDataReaderobjects Typically, in

programming ADO.NET, you first create theConnectionobject and provide it with the necessary

information, such as the connection string You then create aCommandobject and provide it with the

details of the SQL command that is to be executed This command can be an inline SQL text command, a stored procedure, or direct table access You can also provide parameters to these commands if needed After you create theConnectionand theCommandobjects, you must decide whether the command

returns a result set If the command doesn’t return a result set, you can simply execute the command by calling one of its severalExecutemethods On the other hand, if the command returns a result set, you must make a decision about whether you want to retain the result set for future uses without maintain-ing the connection to the database If you want to retain the result set, you must create aDataAdapter

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object and use it to fill aDataSetor aDataTableobject These objects are capable of maintaining their

information in a disconnected mode However, if you don’t want to retain the result set, but rather to

simply process the command in a swift fashion, you can use theCommandobject to create aDataReader

object TheDataReaderobject needs a live connection to the database, and it works as a forward-only,

read-only cursor

Using the Connection Object

TheConnectionobject creates a link (or connection) to a specified data source This object must contain

the necessary information to discover the specified data source and to log in to it properly using a defined

username and password combination This information is provided via a single string called a connection

string You can also store this connection string in theweb.configfile of your application

Every type of data provider has a connection object of some kind The data provider for working with a

SQL data store includes aSqlConnectionclass that performs this type of operation TheSqlConnection

object is a class that is specific to theSqlClientprovider As discussed earlier in this chapter, the

SqlClientprovider is built for working with the SQL Server 7.0 and higher databases The properties

for theSqlConnectionclass are shown in the following table

Property Description

ConnectionString This property allows you to read or provide the connection string that should

be used by theSqlConnectionobject

Database This read-only property returns the name of the database to use after the

connection is opened

Datasource This read-only property returns the name of the instance of the SQL Server

database used by theSqlConnectionobject

State This read-only property returns the current state of the connection The possible

values areBroken,Closed,Connecting,Executing,Fetching, andOpen

Connecting to a data source is probably the most common task when you are working with data This

example and the ones that follow assume that you have a SQL Server database In order to connect to

your SQL Server database, you use theSqlConnectionclass This is shown in Listing 8-5

Listing 8-5: Connecting to a SQL database

VB

Dim conn as SqlConnection

User Instance=True") ’ Put this string on one line in your code conn.Open()

C#

SqlConnection conn;

conn = new

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User Instance=True"); // Put this string on one line in your code conn.Open();

To make this connection work, be sure that the proper namespaces are imported before you start using any of the classes that work with SQL The first step in making a connection is to create an instance of the

SqlConnectionclass and assign it to theconninstance ThisSqlConnectionclass is initialized after you pass in the connection string as a parameter to the class In this case, you are connecting to the Northwind database that resides on your local machine using the system administrator’s login credentials

Another means of making a connection is to put the connection string within the application’sweb.config

file and then to make a reference to theweb.configfile With ASP.NET 3.5, you will find that there is an easy way to manage the storage of your connection strings through the use of theweb.configfile This

is actually a better way to store your connection strings rather than hard-coding them within the code

of the application itself In addition to having a single point in the application where the credentials

for database access can be managed, storing credentials in theweb.configalso gives you the ability to

encrypt the credentials

To define your connection string within theweb.configfile, you are going to make use of the

<connectionStrings>section From this section, you can place an<add>element within it to define

your connection An example of this is illustrated in Listing 8-6

Listing 8-6: Providing your connection string within the web.config file

<connectionStrings>

<add name="DSN_Northwind" connectionString="Data

Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\NORTHWND.MDF;Integrated

Security=True;User Instance=True"

providerName="System.Data.SqlClient" />

</connectionStrings>

In many places of this chapter, you will see that the actual connection string is broken up on multiple

lines This connection string will need to be on a single line within your code or broken up with string

concatenation.

Now that you have a connection string within theweb.configfile, you can then make use of that

connection string directly in your code by using theConnectionManagerobject as illustrated here in

Listing 8-7

Listing 8-7: Using the connection string found in the web.config file

VB

conn = New _

SqlConnection( _

ConfigurationManager.ConnectionStrings("DSN_Northwind").ConnectionString)

C#

conn = new

SqlConnection(

ConfigurationManager.ConnectionStrings["DSN_Northwind"].ConnectionString);

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