You need to familiarize yourself with the following
primary .NET Framework namespaces to be able to program against SQL
Server 2008:
System.Data— This is the root namespace, which contains essential data access classes, such as DataSet, DataTable, and DataRow.
System.Data.SqlClient— This namespace contains classes specialized for SQL Server access, such as SqlConnection, SqlCommand, and SqlParameter.
System.Xml— This namespace holds most of the objects you need to be able to work with SQL Server XML.
System.Linq and System.Data.Linq— These namespaces hold classes essential for working with LINQ to SQL (stored in the new Sytem.Core assembly).
The easiest way to immerse
yourself in the code is to walk through some typical usage scenarios,
which we do in the following sections.
ADO.NET: Advanced Basics
To start coding with ADO.NET
and SQL Server, you first need to connect to an instance of SQL Server.
To do this, you need a connection string. A connection string
is simply a string literal that contains all the parameters necessary
to locate and log in to a server in a semicolon-delimited format. The
following is an example:
"Data Source=(SQLServer001);Initial Catalog=AdventureWorks2008;Integrated Security=True"
There are too many
different connection string parameters to list here; you can check the
MSDN “Connection Strings” topic for full information.
The managed object that represents a SQL Server connection is System.Data.SqlClient.SqlConnection.
This article takes you
through a simple C# Windows application built with Visual Studio 2008
(VS). It contains every manager’s dream: a form with a magic button on
it that does everything with one click. To create this application, open
Visual Studio and create a new C# Windows Forms application
(illustrated in Figure 1). Right-click the file called Form1.cs in Solution Explorer (SE) and select Rename. Change the name to MainForm.cs and accept the rename warning. Next, right-click MainForm.cs again and select View Code. Then type the following namespaces into the using area at the top left:
using System.Data.SqlClient;
using System.Configuration;
Next, right-click the References
folder in the Solution Explorer and choose Add Reference. On the
ensuing Add Reference dialog, click on the .NET tab and then scroll down
until you find System.Configuration.
Select this entry and click OK. Next, right-click the project in the
Solution Explorer and choose Add New Item; then scroll though the
choices that appear in the Add New Item dialog until you find
Application Configuration File. This file is the place where you
typically store connection strings and other configurable parameters.
Open your new App.Config file and enter the following elements, substituting your server name for (local) in the connection string itself:
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<appSettings>
<add
key="SqlConn"
value="Data Source=(local);Initial Catalog=AdventureWorks2008;
Integrated Security=True"/>
</appSettings>
</configuration>
Switching back to MainForm.cs,
right-click the file in Solution Explorer and then select View
Designer, which launches the Visual Studio WinForms designer. Drag a Button control from the Toolbox onto the form and name it btnGo. Next, drag a DataGridView control onto the form and name it GridView (ignore the form designer’s SmartTag); this control will be used to display the data returned when you execute your SqlCommand. The SqlCommand
object allows you to execute T-SQL, including stored procedures,
functions, and other expressions from within the context of an active
SQL Server connection.
SqlCommand has several execution methods, each of which behaves differently and returns a different type of object:
ExecuteNonQuery— Executes the T-SQL statements and returns an Int32
that indicates the number of rows affected. It also populates any
output parameters. This capability is especially useful when you are
executing INSERT and UPDATE queries.
ExecuteScalar— Executes the T-SQL statements and returns an object (of type Object)
that contains the value of the first column of the first row returned.
The object returned is castable to one of the native .NET types (for
example, Int32, String [even for returned xml columns], Boolean).
ExecuteReader— Executes the T-SQL statements and returns a SqlDataReader object. SqlDataReader
objects are useful when you want to perform some behavior on the
returned result set on a per-row and/or per-column basis (usually using a
looping construct).
ExecuteXmlReader— Executes the T-SQL statements and returns a System.Xml.XmlReader, which you can use to iterate through the nodes in selected XML (or to instantiate other System.Xml objects, such as System.Xml.XPath.XPathDocument), produced either via SELECT...FOR XML or from a column or variable of the new xml data type.
Tip
System.Data.SqlClient
also provides asynchronous versions of the preceding method calls in
begin-call/end-call pairs that take a handy callback method parameter,
including BeginExecuteReader, EndExecuteReader, BeginExecuteNonQuery, and EndExecuteNonQuery. Note that there is no BeginExecuteScalar/EndExecuteScalar.
To wire up the data returned from the SqlCommand into a System.Data.DataSet (the storage object for returned results), you need to use an object of type System.Data.SqlClient.SqlDataAdapter. Developers frequently use SqlDataAdapter objects to map data coming from SQL Server into DataSet objects and back, using its Fill() and Update() methods, respectively.
You may also want to include in your code a try-catch exception-handling block that catches any SqlException objects thrown during your code’s execution.
To test the many classes we’ve just mentioned, add the code in Listing 1 to the btnGo_Click()
event handler. To generate the event handler, simply view your form in
the Visual Studio designer and then double-click your button.
Listing 1. A Button Event Handler That Illustrates the Use of Several ADO.NET Objects
private void btnGo_Click(object sender, EventArgs e)
{
using (SqlConnection Connection =
new SqlConnection(ConfigurationManager.AppSettings["SqlConn"]))
{
using (SqlCommand Command =
new SqlCommand(
@"SELECT TOP 10 * FROM Person.Person"
, Connection))
{
try
{
using (SqlDataAdapter Adapter =
new SqlDataAdapter(Command))
{
using (DataSet Set = new DataSet())
{
Connection.Open();
Adapter.Fill(Set);
GridView.DataSource = Set.Tables[0];
}
}
}
catch (SqlException SqlEx)
{
foreach (SqlError SqlErr in SqlEx.Errors)
{
MessageBox.Show(
"The following SQL Error occurred: " + SqlErr.Message,
"SqlError");
}
}
}
}
}
|
Next, run your Windows Forms application (press F5) and then click btnGo. Your form should look something like the one in Figure 2.
This code in your form executes as follows: a connection to SQL Server is made via SqlConnection and the subsequent call to Connection.Open() (which, by the way, is unnecessary because SqlDataAdapter.Fill() implicitly opens the closed connection). The SqlCommand object Command
is set to use this connection via its constructor. The constructor also
takes a string parameter that contains the text of the query. It can
also take the name of a stored procedure, for example. When using a
stored procedure name, you change its CommandType property from the default of CommandType.Text to CommandType.StoredProcedure.
Next, you instantiate a SqlDataAdapter object that registers the Command object as what it will execute on the call to Fill(). You also create a DataSet object to hold the returned data. In the simplest respect, DataSet objects are collections of DataTable objects, which map directly to SQL Server query results. Each DataTableDataRow objects, each of which in turn holds an array of DataColumn values accessible by indexers. object, as you may guess, holds an array of
You bind the DataGridView object to the filled DataSet object’s first table (Tables[0]), and you can rest assured that the catch block will notify you with a message box about each SqlError contained in the Errors collection of any raised SqlException.
Many of the database classes provided in ADO.NET have a Dispose()
method because, under the covers, they utilize unmanaged (COM)
resources. The objects you most commonly use for database applications
that provide Dispose() are SqlConnection, SqlCommand, SqlDataAdapter, SqlDataReader, and DataSet.
Now that you’ve had a taste of
working with some of the traditional ADO.NET objects, it’s time to
forge ahead into the new world of LINQ.
