Beginning C# 2008 Databases From Novice to Professional phần 5 potx

Figure 9-7. Administrative Tools: Data Sources (ODBC) 3. When the ODBC Data Source Administrator window opens, click the User DSN tab and then click Add (see Figure 9-8). Figure 9-8. ODBC Data Source Administrator dialog box CHAPTER 9 ■ GETTING TO KNOW ADO.NET 179 9004ch09final.qxd 12/13/07 4:12 PM Page 179 4. The Create New Data Source wizard starts. Follow its instructions carefully! First, select the SQL Server driver; second, click Finish (see Figure 9-9). Figure 9-9. Create New Data Source wizard 5. The next window prompts for the data source name and server. Specify the values for Name and Server as NorthwindOdbc and .\sqlexpress, respectively, as shown in Figure 9-10, and then click Next. Figure 9-10. Specifying the data source name and SQL Server to connect to CHAPTER 9 ■ GETTING TO KNOW ADO.NET180 9004ch09final.qxd 12/13/07 4:12 PM Page 180 6. Accept the defaults in the authentication window by clicking Next (see Figure 9-11). Figure 9-11. Specifying SQL Server authentication 7. In the next window, check the Change the default database to option, select the Northwind database from the pr ovided drop-down list, and click Next (see Figure 9-12). Figure 9-12. S pecifying the default database CHAPTER 9 ■ GETTING TO KNOW ADO.NET 181 9004ch09final.qxd 12/13/07 4:12 PM Page 181 8. In the next window, simply click Finish (see Figure 9-13). Figure 9-13. Finishing DSN creation 9. A confirmation window appears, describing the new data source. Click Test Data Source (see Figure 9-14). Figure 9-14. Testing the Northwind data source connection CHAPTER 9 ■ GETTING TO KNOW ADO.NET182 9004ch09final.qxd 12/13/07 4:12 PM Page 182 10. A window reporting a successful test should appear (see Figure 9-15). (If it doesn’t, cancel your work and carefully try again.) Click OK. Figure 9-15. Connection to Northwind was successful. 11. When the confirmation window reappears, click OK. When the ODBC Data Source Administrator window reappears, the new data source will be on the list (see Figure 9-16). Click OK. Figure 9-16. N e w data source appearing in the data source list N o w y ou hav e y our N or thwindO dbc data source ready to work with. Next, you will use it in code for setting up the connection str ing. CHAPTER 9 ■ GETTING TO KNOW ADO.NET 183 9004ch09final.qxd 12/13/07 4:12 PM Page 183 Try It Out: Creating a Simple Console Application Using the ODBC Data Provider Let’s access Northwind with ODBC: 1. In Solution Explorer, add a new C# Console Application project named OdbcProvider to the Chapter09 solution. Rename the Program.cs file to OdbcProvider.cs. In the code editor, replace the generated code with the code in Listing 9-3, which shows the changes to Listing 9-1 in bold. Listing 9-3. OdbcProvider.cs using System; using System.Data; using System.Data.Odbc; namespace Chapter04 { class OdbcProvider { static void Main(string[] args) { // set up connection string string connString = @"dsn=northwindodbc"; // set up query string string sql = @" select * from employees "; // declare connection and data reader variables OdbcConnection conn = null; OdbcDataReader reader = null; try { // open connection conn = new OdbcConnection(connString); conn.Open(); CHAPTER 9 ■ GETTING TO KNOW ADO.NET184 9004ch09final.qxd 12/13/07 4:12 PM Page 184 // execute the query OdbcCommand cmd = new OdbcCommand(sql, conn); reader = cmd.ExecuteReader(); // display output header Console.WriteLine( "This program demonstrates the use of " + "the ODBC Data Provider." ); Console.WriteLine( "Querying database {0} with query {1}\n" , conn.Database , cmd.CommandText ); Console.WriteLine("First Name\tLast Name\n"); // process the result set while(reader.Read()) { Console.WriteLine( "{0} | {1}" , reader["FirstName"].ToString().PadLeft(10) , reader[1].ToString().PadLeft(10) ); } } catch (Exception e) { Console.WriteLine("Error: " + e); } finally { // close connection reader.Close(); conn.Close(); } } } } CHAPTER 9 ■ GETTING TO KNOW ADO.NET 185 9004ch09final.qxd 12/13/07 4:12 PM Page 185 2. Make this project the startup program by right-clicking the project name in Solution Explorer and then clicking Set as StartUp Project as shown earlier in the Figure 9-4. 3. Run the application with Ctrl+F5. The results should appear as in Figure 9-17. Figure 9-17. Accessing Northwind via ODBC. How It Works Once you create a DSN, the rest is easy. You simply change Sql to Odbc in the class names (and, of course, the output header), just as you did to modify the program to work with OLE DB. The biggest change, and the only one that really deserves attention, is to the connection string. // set up connection string string connString = @"dsn=northwindodbc"; The ODBC connection string isn’t limited only to the DSN, but it doesn’t allow blanks or newlines anywhere in the string. ■Tip Each data provider has its own rules regarding both the parameters and syntax of its connection string. Consult the documentation for the provider you’re using when coding connection strings. Connection strings can be ver y complicated. We don’t cover the details here, but documentation for connection strings is included with the description of the ConnectionString property for the connection class for each data provider . CHAPTER 9 ■ GETTING TO KNOW ADO.NET186 9004ch09final.qxd 12/13/07 4:12 PM Page 186 Now that you’ve played with all the data providers that access SQL Server (the SQL Server CE data provider is beyond the scope of this book), let’s make sure you clearly understand what a data provider is and how different data providers can be used to access data. Data Providers Are APIs The .NET Framework data providers, sophisticated as they are (and you’ll learn plenty about exploiting their sophistication later), are simply APIs for accessing data sources, most often relational databases. (ADO.NET is essentially one big API of which data providers are a major part.) Newcomers to ADO.NET are often understandably confused by the Microsoft documentation. They read about Connection, Command, DataReader, and other ADO.NET objects, but they see no classes named Connection, Command, or DataReader in any of the ADO.NET namespaces. The reason is that data provider classes implement interfaces in the System.Data namespace. These interfaces define the data provider methods of the ADO.NET API. The key concept is simple. A data provider, such as System.Data.SqlClient, consists of classes whose methods provide a uniform way of accessing a specific kind of data source. In this chapter, you used three different data providers (SQL Server, OLE DB, and ODBC) to access the same SSE database. The only real difference in the code was the connection string. Except for choosing the appropriate data provider, the rest of the programming was effectively the same. This is true of all ADO.NET facilities, whatever kind of data source you need to access. The SQL Server data provider is optimized to access SQL Server and can’t be used for any other DBMS. The OLE DB data provider can access any OLE DB data source—and you used it without knowing anything about OLE DB (a major study in itself). The ODBC data provider lets you use an even older data access technology, again without knowing anything about it. W or king at such an abstract level enabled you to do a lot more, a lot mor e quickly , than y ou could have otherwise. ADO.NET is not only an efficient data access technology, but also an elegant one. Data providers are only one aspect of it. The art of ADO.NET programming is founded more on conceptualizing than on coding. First get a clear idea of what ADO.NET offers, and then look for the right method in the right class to make the idea a reality. Since conceptual clarity is so important, you can view (and refer to) connections, commands, data readers, and other ADO.NET components primarily as abstractions rather than merely objects used in database programs. If you concentrate on concepts, learning when and how to use relevant objects and methods will be easy. CHAPTER 9 ■ GETTING TO KNOW ADO.NET 187 9004ch09final.qxd 12/13/07 4:12 PM Page 187 Summary In this chapter, you saw why ADO.NET was developed and how it supersedes other data access technologies in .NET. We gave an overview of its architecture and then focused on one of its core components, the data provider. You built three simple examples to prac- tice basic data provider use and experience the uniform way data access code is written, regardless of the data provider. Finally, we offered the opinion that conceptual clarity is the key to understanding and using both data providers and the rest of the ADO.NET API. Next, we’ll study the details of ADO.NET, starting with connections. CHAPTER 9 ■ GETTING TO KNOW ADO.NET188 9004ch09final.qxd 12/13/07 4:12 PM Page 188 [...]... debugging, to verify that the connection properties are what you expect them to be Here, we’ll describe the connection properties common to most data providers Try It Out: Displaying Connection Information In this example, you’ll see how to write a program to display connection information 1 Add a C# Console Application project named ConnectionDisplay to the Chapter10 solution 2 Rename Program.cs to ConnectionDisplay.cs... database to connect to, so you’ll use OLE DB with SSE, as you did in Chapter 9 2 05 9004ch10final.qxd 206 12/13/07 4:10 PM Page 206 CHAPTER 10 s MAKING CONNECTIONS Try It Out: Connecting to SQL Server Express with the OLE DB Data Provider To connect to SSE with the OLE DB data provider, follow these steps: 1 Add a C# Console Application project named ConnectionOleDb, and rename Program.cs to ConnectionOleDb.cs... installed—go back to Chapter 1 and follow the instructions there for installing SSE • A security problem exists—your Windows login and password aren’t valid on the server This is unlikely to be the problem when connecting to a local SSE instance, but it might happen in trying to connect to a SQL Server instance on another server • A hardware problem exists—again unlikely if you’re trying to connect to a server... so you were connected to the SQL Server’s default database master If you wanted to connect to the Northwind database, you’d need to specify the Database parameter, for example: // connection string string connString = new SqlConnection(@" server = \sqlexpress; integrated security = true; database = northwind "; You can also change the default database from the master database to some other database,... Debugging Connections to SQL Server Writing the C# code to use a connection is usually the easy part of getting a connection to work Problems often lie not in the code, but rather in a mismatch in the connection parameters between the client (your C# program) and the database server All appropriate connection parameters must be used and must have correct values Even experienced database professionals often... also saw how to handle various exceptions associated with connections In the next chapter, you’ll look at ADO.NET commands and see how to use them to access data 9004ch11final.qxd 12/13/07 4:08 PM CHAPTER Page 209 11 Executing Commands O nce you’ve established a connection to the database, you want to start interacting with it and getting it doing something useful for you You may need to add, update,... Property To set the Connection property, follow these steps: 1 Add the following bold code to the try block of Listing 11-1 try { // open connection conn.Open(); // connect command to connection cmd.Connection = conn; Console.WriteLine("Connnected command to this connection."); } 2 Run the code by pressing Ctrl+F5 You should see the results in Figure 11-2 Figure 11-2 Connecting a command to a connection... connection to the command’s Connection property that they become associated // connect command to connection cmd.Connection = conn; Console.WriteLine("Connected command to this connection."); The actual assignment occurs after the call to conn.Open in this particular example, but you could have done it before calling Open(); the connection doesn’t have to be open for the Connection property of the command to. .. with a Connection For your commands to be executed against a database, each command must be associated with a connection to the database You do this by setting the Connection property of the command, and in order to save resources, multiple commands can use the same connection You have a couple of ways to set up this association, so next you’ll modify the example to try them 211 9004ch11final.qxd 212... specific to a particular database You used connections in Chapter 9 Let’s take a closer look at one of them, SqlConnection, in the namespace System.Data.SqlClient Connecting to SQL Server Express with SqlConnection In this example, you’ll again connect to the SQL Server connect to the SQL Server Express (SSE) Northwind database Try It Out: Using SqlConnection You’ll write a very simple program, just to open . connecting to a local SSE instance, but it might happen in trying to connect to a SQL Server instance on another server. • A hardware problem exists—again unlikely if you’re trying to connect to a. of connection errors. Debugging Connections to SQL Server Writing the C# code to use a connection is usually the easy part of getting a connec- tion to work. Problems often lie not in the code,. Solution Explorer, add a new C# Console Application project named OdbcProvider to the Chapter09 solution. Rename the Program.cs file to OdbcProvider.cs. In the code editor, replace the generated