ASP.NET 4 Unleased - p 88 doc

The different implementations of the Connection, Command, and DataReader classes are grouped into the following namespaces:.. Because ADO.NET follows the Provider model, all implementati

You also learn how to build Microsoft SQL Server database objects, such as stored

proce-dures and user-defined types, by using NET Framework For example, you learn how to

write a Microsoft SQL Server stored procedure, using C# programming language

NOTE

If you don’t want to get your hands dirty touching any actual SQL or ADO.NET code, skip

this chapter and read Chapter 20, “Data Access with LINQ to SQL.” LINQ to SQL

enables you to access the database without writing any ADO.NET or SQL code

Connected Data Access

The ADO.NET Framework encompasses a huge number of classes However, at its heart, it

actually consists of the following three classes:

Connection—Enables you to represent a connection to a data source

Command—Enables you to execute a command against a data source

DataReader—Enables you to represent data retrieved from a data source

Most of the other classes in ADO.NET Framework are built from these three classes These

three classes provide you with the fundamental methods of working with database data

They enable you to connect to a database, execute commands against a database, and

represent the data returned from a database

Now that you understand the importance of these three classes, it’s safe to tell you that

they don’t actually exist ADO.NET uses the Provider model You use different sets of

ADO.NET classes for communicating with different data sources

For example, there is no such thing as the Connection class Instead, there are the

SqlConnection, OracleConnection, OleDbConnection, and ODBCConnection classes You use

different Connection classes to connect to different data sources

The different implementations of the Connection, Command, and DataReader classes are

grouped into the following namespaces:

System.Data.SqlClient—Contains ADO.NET classes for connecting to Microsoft

SQL Server version 7.0 or higher

System.Data.OleDb—Contains ADO.NET classes for connecting to a data source with

an OLEDB provider

System.Data.Odbc—Contains ADO.NET classes for connecting to a data source with

an ODBC driver

System.Data.OracleClient—Contains ADO.NET classes for connecting to an Oracle

database (requires Oracle 8i Release 3/8.1.7 Client or later)

System.Data.SqlServerCe—Contains ADO.NET classes for connecting to SQL Server

Mobile

If you connect to Microsoft SQL Server 7.0 or higher, you should always use the classes

from the SqlClient namespace These classes provide the best performance because they

connect directly to SQL Server at the level of the Tabular Data Stream (the low-level

proto-col that Microsoft SQL Server uses to communicate with applications)

Of course, there are other databases in the world than Microsoft SQL Server If you are

communicating with an Oracle database, you should use the classes from the

OracleClient namespace If you are communicating with another type of database, you

need to use the classes from either the OleDb or Odbc namespaces Just about every

data-base created by man has either an OLEDB provider or an ODBC driver

Because ADO.NET follows the Provider model, all implementations of the Connection,

Command, and DataReader classes inherit from a set of base classes Here is a list of these

base classes:

DbConnection—The base class for all Connection classes

DbCommand—The base class for all Command classes

DbDataReader—The base class for all DataReader classes

These base classes are contained in the System.Data.Common namespace

All the sample code in this chapter assumes that you work with Microsoft SQL Server

Therefore, all the sample code uses the classes from the SqlClient namespace However,

because ADO.NET uses the Provider model, the methods that you would use to work with

another database are similar to the methods described in this chapter

NOTE

Before you can use the classes from the SqlClient namespaces in your components

and pages, you need to import the System.Data.SqlClient namespace

Before we examine the Connection, Command, and DataReader classes in detail, let’s look at

how you can build a simple data access component with these classes The component in

Listing 19.1, named Movie1, includes a method named GetAll() that returns every record

from the Movies database table

LISTING 19.1 App_Code\Movie1.cs

using System;

using System.Data;

using System.Data.SqlClient;

using System.Web.Configuration;

using System.Collections.Generic;

public class Movie1

{

private static readonly string _connectionString;

private string _title;

private string _director;

public string Title

{

get { return _title; }

set { _title = value; }

}

public string Director

{

get { return _director; }

set { _director = value; }

}

public List<Movie1> GetAll()

{

List<Movie1> results = new List<Movie1>();

SqlConnection con = new SqlConnection(_connectionString);

SqlCommand cmd = new SqlCommand(“SELECT Title,Director FROM Movies”, con);

using (con)

{

con.Open();

SqlDataReader reader = cmd.ExecuteReader();

while (reader.Read())

{

Movie1 newMovie = new Movie1();

newMovie.Title = (string)reader[“Title”];

newMovie.Director = (string)reader[“Director”];

results.Add(newMovie);

}

}

return results;

}

static Movie1()

{

_connectionString =

WebConfigurationManager.ConnectionStrings[“Movies”].ConnectionString;

}

}

In Listing 19.1, a SqlConnection object represents a connection to a Microsoft SQL Server

database A SqlCommand object represents a SQL SELECT command The results of executing

the command are represented with a SqlDataReader

Each row returned by the SELECT command is retrieved by a call to the

SqlDataReader.Read() method from within a While loop When the last row is retrieved

from the SELECT command, the SqlDataReader.Read() method returns False and the

While loop ends

Each row retrieved from the database is added to a List collection An instance of the

Movie1 class represents each record

The page in Listing 19.2 uses a GridView and ObjectDataSource control to display the

records returned by the Movie1 data access component (see Figure 19.1)

FIGURE 19.1 Displaying movie records

LISTING 19.2 ShowMovie1.aspx

<%@ Page Language=”C#” %>

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN”

“http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”>

<html xmlns=”http://www.w3.org/1999/xhtml” >

<head id=”Head1” runat=”server”>

<title>Show Movie1</title>

</head>

<body>

<form id=”form1” runat=”server”>

<div>

<asp:GridView

id=”grdMovies”

DataSourceID=”srcMovies”

Runat=”server” />

<asp:ObjectDataSource

id=”srcMovies”

TypeName=”Movie1”

SelectMethod=”GetAll”

Runat=”server” />

</div>

</form>

</body>

</html>

Using the Connection Object

The Connection object represents a connection to a data source When you instantiate a

Connection, you pass a connection string to the constructor, which contains information

about the location and security credentials required for connecting to the data source

For example, the following statement creates a SqlConnection that represents a

connec-tion to a Microsoft SQL Server database named Pubs that is located on the local machine:

SqlConnection con = new SqlConnection(“Data Source=localhost;Integrated

➥Security=True;Initial Catalog=Pubs”);

For legacy reasons, there are a number of ways to write a connection string that does

exactly the same thing For example, the keywords Data Source, Server, Address, Addr,

and Network Address are all synonyms You can use any of these keywords to specify the

location of the database server

NOTE

You can use the SqlConnectionStringBuilder class to convert any connection string

into canonical syntax For example, this class replaces the keyword Server with the

keyword Data Source in a connection string

Before you execute any commands against the data source, you first must open the

connection After you finish executing commands, you should close the connection as

quickly as possible

A database connection is a valuable resource Strive to open database connections as late

as possible, and close database connections as early as possible Furthermore, always

include error handling code to make sure that a database connection gets closed even

when there is an exception

For example, you can take advantage of the Using statement to force a connection to close

even when an exception is raised, like this:

SqlConnection con = new SqlConnection(“Data Source=localhost;

Integrated Security=True;Initial Catalog=Pubs”);

SqlCommand cmd = new SqlCommand(“INSERT Titles (Title) VALUES (‘Some Title’)”, con);

using (con)

{

con.Open();

cmd.ExecuteNonQuery();

}

The using statement forces the connection to close, regardless of whether an error occurs

when a command is executed against the database The using statement also disposes of

the Connection object (If you need to reuse the Connection, you need to reinitialize it.)

Alternatively, you can use a try catch statement to force a connection to close like this:

SqlConnection con = new SqlConnection(“Data Source=localhost;Integrated

Security=True;Initial Catalog=Pubs”);

SqlCommand cmd = new SqlCommand(“INSERT Titles (Title) VALUES (‘Some Title’)”, con);

try

{

con.Open();

cmd.ExecuteNonQuery();

}

finally

{

con.Close();

}

The finally clause in this try catch statement forces the database connection to close

both when there are no errors and when there are errors

Retrieving Provider Statistics

When you use the SqlConnection object, you can retrieve statistics about the database

commands executed with the connection For example, you can retrieve statistics on total

execution time

The GetAll() method exposed by the component in Listing 19.3 includes a parameter

named executionTime After the database command executes, the value of executionTime

is retrieved from the Connection statistics

LISTING 19.3 App_Code\Movie2.cs

using System;

using System.Data;

using System.Data.SqlClient;

using System.Web.Configuration;

using System.Collections;

using System.Collections.Generic;

public class Movie2

{

private static readonly string _connectionString;

private string _title;

private string _director;

public string Title

{

get { return _title; }

set { _title = value; }

}

public string Director

{

get { return _director; }

set { _director = value; }

}

public List<Movie2> GetAll(out long executionTime)

{

List<Movie2> results = new List<Movie2>();

SqlConnection con = new SqlConnection(_connectionString);

SqlCommand cmd = new SqlCommand(“WAITFOR DELAY ‘0:0:03’;SELECT Title,Director

FROM Movies”, con);

con.StatisticsEnabled = true;

using (con)

{

con.Open();

SqlDataReader reader = cmd.ExecuteReader();

while (reader.Read())

{

Movie2 newMovie = new Movie2();

newMovie.Title = (string)reader[“Title”];

newMovie.Director = (string)reader[“Director”];

results.Add(newMovie);

}

}

IDictionary stats = con.RetrieveStatistics();

executionTime = (long)stats[“ExecutionTime”];

return results;

}

static Movie2()

{

_connectionString =

WebConfigurationManager.ConnectionStrings[“Movies”].ConnectionString;

}

}

In Listing 19.3, the SqlConnection.StatisticsEnabled property is set to the value True

You must enable statistics before you can gather statistics After the command executes, a

dictionary of statistics is retrieved with the SqlConnection.RetrieveStatistics()

method Finally, you retrieve the executionTime by looking up the ExecutionTime key in

the dictionary

NOTE

In Listing 19.3, the SQL WAITFOR statement is used to pause the execution of the

SELECT command for three seconds so that a more interesting execution time is

retrieved from the ExecutionTime statistic Because the SELECT command is such a

simple command, if you don’t add a delay, you often receive an execution time of 0

milliseconds

The page in Listing 19.4 illustrates how you can use this component to display both the

results of a database query and the database query execution time (see Figure 19.2)

LISTING 19.4 ShowMovie2.aspx

<%@ Page Language=”C#” %>

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN”

“http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”>

<script runat=”server”>

protected void srcMovies_Selected(object sender,

➥ObjectDataSourceStatusEventArgs e)

{

lblExecutionTime.Text = e.OutputParameters[“executionTime”].ToString();

}

</script>

<html xmlns=”http://www.w3.org/1999/xhtml” >

<head id=”Head1” runat=”server”>

<title>Show Movie2</title>

</head>

<body>

FIGURE 19.2 Displaying execution time statistics

<form id=”form1” runat=”server”>

<div>

<asp:GridView

id=”grdMovies”

DataSourceID=”srcMovies”

Runat=”server” />

<asp:ObjectDataSource

id=”srcMovies”

TypeName=”Movie2”

SelectMethod=”GetAll”

Runat=”server” OnSelected=”srcMovies_Selected”>

<SelectParameters>

<asp:Parameter Name=”executionTime” Type=”Int64” Direction=”Output” />

</SelectParameters>

</asp:ObjectDataSource>

<br />

Execution time was

<asp:Label

id=”lblExecutionTime”

Runat=”server” />

milliseconds

</div>

</form>

</body>

</html>

The SqlConnection object supports the following properties and methods related to

gath-ering statistics:

StatisticsEnabled—Enables you to turn on statistics gathering

RetrieveStatistics()—Enables you to retrieve statistics represented with an

IDictionary collection

ResetStatistics()—Resets all statistics to 0

You can call the RetrieveStatistics() method multiple times on the same

SqlConnection Each time you call the method, you get another snapshot of the

Connection statistics