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CHAPTER 9 s GETTING TO KNOW ADO.NET
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choose the best provider for your purpose. Given the performance benefits of the serverspecific data providers, if you use SQL Server, 99% of the time you should be using the System. Data.SqlClient classes. Before we look at what each kind of data provider does and how it s used, you need to be clear on its core functionality. Each .NET data provider is designed to do the following two things very well: Provide access to data with an active connection to the data source Provide data transmission to and from disconnected datasets and data tables Database connections are established by using the data provider s connection class (for example, System.Data.SqlClient.SqlConnection). Other components such as data readers, commands, and data adapters support retrieving data, executing SQL statements, and reading or writing to datasets or data tables, respectively. As you ve seen, each data provider is prefixed with the type of data source it connects to (for instance, the SQL Server data provider is prefixed with Sql), so its connection class is named SqlConnection. The OLE DB data provider s connection class is named OleDbConnection. Let s see how to work with the three data providers that can be used with SQL Server.
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Working with the SQL Server Data Provider
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The .NET data provider for SQL Server is in the System.Data.SqlClient namespace. Although you can use System.Data.OleDb to connect with SQL Server, Microsoft has specifically designed the System.Data.SqlClient namespace to be used with SQL Server, and it works in a more efficient and optimized way than System.Data.OleDb. The reason for this efficiency and optimized approach is that this data provider communicates directly with the server using its native network protocol instead of through multiple layers. Table 9-2 describes some important classes in the SqlClient namespace. Table 9-2. Commonly Used SqlClient Classes
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Classes
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SqlCommand SqlConnection SqlDataAdapter SqlDataReader SqlError SqlException SqlParameter SqlTransaction
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Executes SQL queries, statements, or stored procedures Represents a connection to a SQL Server database Represents a bridge between a dataset and a data source Provides a forward-only, read-only data stream of the results Holds information on SQL Server errors and warnings Defines the exception thrown on a SQL Server error or warning Represents a command parameter Represents a SQL Server transaction
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CHAPTER 9 s GETTING TO KNOW ADO.NET
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Another namespace, System.Data.SqlTypes, maps SQL Server data types to .NET types, both enhancing performance and making developers lives a lot easier. Let s look at an example that uses the SQL Server data provider. It won t cover connections and data retrieval in detail, but it will familiarize you with what you ll encounter in upcoming chapters.
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Try It Out: Creating a Simple Console Application Using the SQL Server Data Provider
You ll build a simple Console Application project that opens a connection and runs a query, using the SqlClient namespace against the SQL Server Management Studio Express (SSMSE) Northwind database. You ll display the retrieved data in a console window. 1. Open Visual Studio 2008 and create a new Visual Basic Console Application project named 09. 2. Right-click the 09 project and rename it to SqlServerProvider. 3. Right-click the Module1.vb file and rename it to SqlServerProvider.vb. When prompted to rename all references to Program, you can click either Yes or No. 4. Since you ll be creating this example from scratch, open SqlServerProvider.vb in the code editor and replace it with the code in Listing 9-1. Listing 9-1. SqlServerProvider.vb Imports System Imports System.Data Imports System.Data.SqlClient Module SqlServerProvider Sub Main() 'Set up connection string Dim conn As New SqlConnection conn.ConnectionString = "Data Source=.\sqlexpress;" & _ "Initial Catalog=Northwind;Integrated Security=True" 'Set up query string Dim sql As String = "select * from employees" 'Declare data reader variables Dim reader As SqlDataReader = Nothing Try ' Open connection conn.Open()
CHAPTER 9 s GETTING TO KNOW ADO.NET
' Execute the query Dim cmd As New SqlCommand(sql, conn) reader = cmd.ExecuteReader() ' Display output header Console.WriteLine("This program demonstrates the use of " & _ "the SQL Server Data Provider.") Console.WriteLine("Querying database {0} with query {1}" & _ ControlChars.NewLine, conn.Database, cmd.CommandText) Console.WriteLine("First Name" + ControlChars.Tab & _ "Last Name" + ControlChars.Lf) ' Process the result set While reader.Read() Console.WriteLine("{0} | {1}", _ reader("FirstName").ToString().PadLeft(10), _ reader(1).ToString().PadLeft(10)) End While Catch e As Exception Console.WriteLine("Error: ", e) Finally ' Close reader and connection reader.Close() conn.Close() End Try End Sub End Module 5. Save the project, and press Ctrl+F5 to run it. The results should appear as in Figure 9-3.
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