Microsoft SQL Server 2008 R2 Unleashed- P184 pptx

ptg 1784 CHAPTER 44 Advanced Stored Procedure Programming and Optimization Table 44.2 lists the general categories of extended stored procedures. Using xp_cmdshell One of the most useful, and potentially dangerous, extended stored procedures provided with SQL Server 2008 is xp_cmdshell. xp_cmdshell can execute any operating system command or program available on the SQL Server system, as long as it is a console program that doesn’t require user input. xp_cmdshell accepts a varchar(8000) (or nvarchar(4000)) value as the command string to be executed, and it returns the results of the command as a single nvarchar(255) column. The full syntax of xp_cmdshell is as follows: xp_cmdshell { ‘command_string’ } [ , no_output ] If the no_output option is specified, the results from the command are not displayed. The following example uses xp_cmdshell to list the files in a directory on the SQL Server computer’s hard disk: EXEC xp_cmdshell ‘DIR c:\*.*’ xp_cmdshell runs synchronously. Control is not returned to the SQL Server user session until the shell command completes. This is why you have to ensure that the shell command invoked via xp_cmdshell does not prompt for user input. Commands invoked via xp_cmdshell do not run interactively, so there is no way to respond to the user input prompt. The SQL Server session waits indefinitely for a command invoked via xp_cmdshell to return. TABLE 44.2 Extended Stored Procedures Categories Category Description General extended proce- dures Provide general functionality. Perhaps the most useful is xp_cmdshell, which executes external programs and returns the output from them as a result set. SQL Mail extended proce- dures Enable you to perform email operations from within SQL Server. SQL Server Profiler extended procedures Are used by SQL Server Profiler. They can also be used directly, for instance, to create a trace queue and start the trace from within a stored procedure. OLE automation procedures Allow SQL Server to create and use OLE automation objects. API system stored proce- dures Are undocumented extended stored procedures used by the API libraries. The server cursor functionality, for instance, is imple- mented as a set of extended stored procedures. ptg 1785 Using Extended Stored Procedures 44 CAUTION After SQL Server passes off the xp_cmdshell command to the operating system, SQL Server cannot interact with the command. If the command requires user input, the process waits indefinitely, and it usually doesn’t go away without a fight. Killing the process in SQL Server usually just leaves it in a KILLED/ROLLBACK state. Closing the session that invoked the xp_cmdshell statement doesn’t help either. Sometimes, you might have to stop and restart SQL Server to make the process finally go away. Alternatively, you may be able to use Task Manager on the system where SQL Server is running to identify the system process that corresponds to the process invoked by xp_cmdshell and end the process. If xp_cmdshell is invoked from another database, it has to be fully qualified as master xp_cmdshell. Unlike with system procedures, SQL Server doesn’t automatically look for extended stored procedures in the master database. Because of the potentially dangerous nature of xp_cmdshell (it essentially allows a user to run operating system–level commands on the SQL Server machine), it is disabled by default. To enable xp_cmdshell, you must run the following commands: EXEC sp_configure ‘show advanced options’, 1 GO RECONFIGURE GO To enable the feature. EXEC sp_configure ‘xp_cmdshell’, 1 GO RECONFIGURE GO As an additional security measure in SQL Server 2008, by default, permission to execute xp_cmdshell is limited to users with CONTROL SERVER permission. The Windows process spawned by xp_cmdshell runs within the security context of the account under which the SQL Server service is running. Essentially, it has the same security rights as the SQL Server service account. When xp_cmdshell is invoked by a user who is not a member of the sysadmin fixed server role, it fails unless a proxy account has been set up. A proxy account is a Windows account that a system administrator defines and sets a security context for within the Windows environment. When a user who is not a member of the sysadmin group runs xp_cmdshell, the commands are run within the security context of the defined proxy account. The proxy account for xp_cmdshell can be created by executing sp_xp_cmdshell_proxy_account. The syntax of this command is as follows: sp_xp_cmdshell_proxy_account [ NULL | { ‘account_name’ , ’password’ } ] ptg 1786 CHAPTER 44 Advanced Stored Procedure Programming and Optimization For example, the following command creates a proxy credential for the Windows domain user Developer\tom that has the Windows password ss2k5Unl: sp_xp_cmdshell_proxy_account ‘Developer/tom’ , ‘ss2k5Unl’ If NULL is passed as account_name, the proxy credential is deleted. CAUTION Because of the potential havoc that could be wreaked on your database server if xp_cmdshell got into the wrong hands, it is recommended that the capability to run xp_cmdshell be left disabled. If you must use xp_cmdshell, be very careful about who has access to it by limiting it to only those with sysadmin permissions if at all possible. If for some reason xp_cmdshell must be made available to all users, be sure that the permissions granted to the proxy account are restricted to the minimum permissions required to perform the commands that need to be invoked via xp_cmdshell. Summary Stored procedures in SQL Server can be very powerful, especially when they take advan- tage of the many features of the T-SQL language. Very complex tasks can be simplified into a single stored procedure call. The guidelines and tips presented in this chapter should help you create more powerful, efficient, and robust stored procedures. Additionally, with the ability to create .NET CLR stored procedures, you can write even more powerful stored procedures in languages other than T-SQL to further expand the capabilities and power of the stored procedures that reside in SQL Server. ptg CHAPTER 45 SQL Server and the .NET Framework IN THIS CHAPTER . What’s New in SQL Server 2008 and the .NET Framework . Getting Comfortable with ADO.NET 3.5 and SQL Server 2008 . Developing with LINQ to SQL . Using ADO.NET Data Services . Leveraging the Microsoft Sync Framework This chapter examines the deep integration of the .NET Framework with SQL Server 2008. It first teaches the essen- tials of programming with ADO.NET 3.5, then it jump- starts your LINQ to SQL skills, and finally it delves into ADO.NET Data Services (formerly Astoria) and the Microsoft Sync Framework. What’s New in SQL Server 2008 and the .NET Framework The release of the .NET Framework 3.5 includes a number of exciting new SQL Server features, the most compelling of which is Language-Integrated Query (LINQ). LINQ to SQL is a timesaving and powerful technology that enables devel- opers to write code in either C# or VB .NET, rather than T- SQL, to query SQL Server databases. ADO.NET Data Services is another new technology that makes it easy to work with SQL Server data in web applica- tions, websites, Rich Internet Applications (RIAs), and other programs that need to consume data from the Web. This chapter shows you how to get started with a simple web application that exposes your data over HTTP. Finally, this chapter covers the Microsoft Sync Framework and how to use it for your occasionally connected applica- tions. ptg 1788 CHAPTER 45 SQL Server and the .NET Framework Getting Comfortable with ADO.NET 3.5 and SQL Server 2008 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 semi- colon-delimited format. The following is an example: ”Data Source=(SQLServer001);Initial Catalog=AdventureWorks2008;Integrated Security=True” This connection string tells ADO.NET to connect to a server called SQLServer001, change to the AdventureWorks2008 database context, and use integrated Windows security to connect, which means it should use the credentials of the currently authenticated user (in web applications, this is usually ASPNET, unless impersonation is used). You typically want to store this connection string in your application’s .config file, preferably encrypted. 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 chapter 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 45.1). Right-click the file called Form1.cs in Solution Explorer (SE) and select Rename. Change the name to MainForm.cs ptg 1789 Getting Comfortable with ADO.NET 3.5 and SQL Server 2008 45 FIGURE 45.1 Creating a new C# Windows Forms application with Visual Studio 2008. 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> ptg 1790 CHAPTER 45 SQL Server and the .NET Framework 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 indi- cates 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. ptg 1791 Getting Comfortable with ADO.NET 3.5 and SQL Server 2008 45 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 45.1 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 45.1 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”); } } } } } ptg 1792 CHAPTER 45 SQL Server and the .NET Framework FIGURE 45.2 Using ADO.NET in a simple Windows Forms application. Next, run your Windows Forms application (press F5) and then click btnGo. Your form should look something like the one in Figure 45.2. 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 DataTable object, as you may guess, holds an array of DataRow objects, each of which in turn holds an array of DataColumn values accessible by indexers. 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. NOTE One convention used in the code in this chapter is nested using statements with these objects. When you use this C# syntax convention, you don’t have to set up a finally block that calls Dispose() for every object; using does that implicitly for you. ptg 1793 Developing with LINQ to SQL 45 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. Developing with LINQ to SQL LINQ enables developers to write code in either C# or VB.NET using the same set of syntactic conventions to query object collections (known as LINQ to Objects), XML docu- ments (known as LINQ to XML), SQL Server data (known as LINQ to SQL), and other queryable resources. The focus in the following sections is exclusively on LINQ to SQL. A LINQ to SQL statement is translated into an in-memory data structure known as an expression tree. An expression tree is an abstract representation of executable code. These trees provide a means for translating LINQ expressions into something else—in the case of LINQ to SQL, T-SQL statements. Once translated into T-SQL, the code is executed on SQL Server (not in .NET). This point is important because it highlights the fact that LINQ is independent from its various data providers. Another important point is that the T-SQL produced by LINQ is not executed until the moment in your .NET code when your LINQ to SQL query is first utilized, not where it is first defined. You may, for example, declare a LINQ to SQL statement near the top of your .NET method but then only actually use it in one branch of an if-else block. This provides enormous efficiency. We should also mention that a certain amount of trust is involved in using LINQ to SQL because it requires you to accept the fact that Microsoft’s LINQ team has made most of the right decisions in doing this translation work (and it has). This does not mean that, as a .NET developer, you no longer need to learn T-SQL; on the contrary, there is much more to T-SQL that LINQ simply doesn’t do, and you will run into its limitations if you use it a lot. It does mean, however, that you can save an immense amount of time in developing data-driven applications because you no longer have to do the repetitive work of writing T-SQL stored procedures for every simple create, retrieve, update, and delete (CRUD) query. Getting Started To start with LINQ to SQL, launch Visual Studio 2008, then right-click your sample project in Solution Explorer, and choose Add New Item. Click on the Data folder on the left side of the ensuing dialog and then select the LINQ to SQL Classes item on the right. Name your new file AdventureWorks2008 and click OK (illustrated in Figure 45.3). . (SqlException SqlEx) { foreach (SqlError SqlErr in SqlEx.Errors) { MessageBox.Show( “The following SQL Error occurred: “ + SqlErr.Message, “SqlError”); } } } } } ptg 1792 CHAPTER 45 SQL Server and. T -SQL to further expand the capabilities and power of the stored procedures that reside in SQL Server. ptg CHAPTER 45 SQL Server and the .NET Framework IN THIS CHAPTER . What’s New in SQL Server 2008. them as a result set. SQL Mail extended proce- dures Enable you to perform email operations from within SQL Server. SQL Server Profiler extended procedures Are used by SQL Server Profiler. They