Figure 8-13: Use Server Explorer to view the structure of the database in Visual C#.NET

Encoding Code 39 Extended in Visual C#.NET Figure 8-13: Use Server Explorer to view the structure of the database

The example works with the Customers table Drag and drop the Customers table from Server Explorer to the left pane of the NWindDataClassesdbml file as shown in Figure 8-14 If you d wanted to work with a sproc, you d place it in the right pane instead The IDE shows where you should place the elements by displaying a plus sign in the correct pane

The design is finished at least for this example You can add as many or as few items as you want from the Northwind database Now it s time to create the query code The output from this example looks the same as the manual method described in the Creating the Simple SQL Server Query Example section of the chapter Listing 8-2 shows the code you need for this example

private void btnTest_Click(object sender, EventArgs e) { // Define the data context NWindDataClassesDataContext DB = new NWindDataClassesDataContext(); // Create the query var DataOut = DBCustomersWhere( ThisArea => ThisAreaRegion == OR ); // Display the results dgResultsDataSource = DataOut; } When working with O/R Designer, you don t need to define an XML mapping source or specify a connection string because the system already has this

information The connection string you create as part of your connection to SQL Server and the visual design shown in Figure 8-14 contain the mapping source Consequently, the code in Listing 8-2 is considerably shorter and even easier to understand than the code in Listing 8-1 You aren t getting anything free; you just define it in a different way The example still requires that you create a data context and this data context still defines the connection to the database for the query After the code defines the data context, it creates a query, DataOut The query still produces output that you can use directly with the dgResultsDataSource property In this case, the query uses a lambda expression; you can also use the same syntax shown in Listing 8-1 if desired When you run this example, you see the same output as shown in Figure 8-9 An O/R Designer application doesn t require the entity classes or XML mapping files used by the manual method In fact, you want to avoid adding these two files to prevent confusion You need only the DBML file that O/R Designer creates for you

As with the other providers discussed in this book, LINQ to SQL Server includes some changes to standard operators The changes modify how the standard operators work so that they perform better with databases One of the biggest issues to consider is that SQL Server generally deals with unordered sets of information Ordering occurs as a post-processing function, rather than as part of defining the intermediate results NET Framework, on the other hand, relies on ordered sets of data For example, if your query uses both the Take and OrderBy operators, the LINQ query will normally show the OrderBy operator first and the Take operator second Due to limits in SQL, however, the translated SQL query will have the SELECT TOP (corresponding to Take) argument first and the ORDER BY argument second The difference in the two environments means that LINQ must perform additional processing in some cases and won t support specific functionality in others SQL queries also produce multisets (bags), rather than sets as NET Framework expects The reason for this difference is that in SQL, identity is defined by value rather than position Therefore, the identity of an element is different in LINQ than it is in SQL Table 8-1 shows the differences in standard operator performance for LINQ to SQL Server