ASP.NET PDF Viewer using C#, VB/NET

Attaches the class specified in className to the control. It must be a valid, defined CSS class available to the host page. Passes focus to the control. If the control is off the page, scrolls the page until it is in view. Unattaches the CSS class specified in className. If the CSS className is currently attached, unattaches it; otherwise, attaches it.

database. So looking at the code from Example 14-3, the statement shown in Example 14-9 does not get anything from the database.

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Caution The points used expect the up and down buttons to appear as they do in the Windows XP style.

var orders = from order in dbContext.SalesOrderHeaders where order.OrderDate == orderDate select order;

As always with LINQ, a query expression only defines a query orders is an object that knows what it s supposed to return if anything happens to enumerate it. So it s the foreach loop in Example 14-3 that kicks off the actual request. The way the EF processes the request is different from how LINQ to Objects works. LINQ to Objects works by forming a chain of operators that work sequentially the source collection might pass through the Where operator, followed by, say, an OrderBy or a Group operator. The Where operator in LINQ to Objects works by walking through every single item in the source, discarding the ones that don t meet the filter criteria, and the ones that do meet the criteria get passed on to the next item in the chain. We really don t want data access code to work that way, and as mentioned earlier, the EF lets the database do the filtering, which is far more efficient than fetching an entire table and then filtering the items in code. We ll now verify that it really works this way by using the SQL Profiler tool to examine what the EF does for us.

SQL Profiler is not part of SQL Server 2008 Express, not even if you install the version with advanced services and Management Studio. You will need a full edition of SQL Server. (The Developer edition will do.) SQL Profiler works just fine with the Express version of the database, but it s distributed and licensed only as part of the fuller editions. As long as you have a suitable license, you can install just the tools from a full edition SQL Server onto a machine that has only the Express version of the database, and it will work just fine. (Unfortunately, if you already installed the Express version of Management Studio, you can t install the full management tools on the same machine.) A full description of the SQL Profiler is beyond the scope of this book we re using it to show you exactly what the Entity Framework asked the database to do. However, it s a profoundly useful tool; even if you use it only for the simple task of discovering what SQL queries are being executed. If you plan to do much work with databases, it s well worth learning how to use it.

Listing 16-18. Testing changing the value by using mouse interaction void SpinBoxTest::testClicks() { QSpinBox spinBox; spinBox.setRange( 1, 10 ); spinBox.setValue( 5 ); QSize size = spinBox.size(); QPoint upButton = QPoint( size.width()-2, 2 ); QPoint downButton = QPoint( size.width()-2, size.height()-2 ); QTest::mouseClick( &spinBox, Qt::LeftButton, 0, upButton ); QCOMPARE( spinBox.value(), 6 ); QTest::mouseClick( &spinBox, Qt::LeftButton, 0, downButton ); QCOMPARE( spinBox.value(), 5 ); spinBox.setValue( 10 ); QTest::mouseClick( &spinBox, Qt::LeftButton, 0, upButton ); QCOMPARE( spinBox.value(), 10 ); spinBox.setValue( 1 ); QTest::mouseClick( &spinBox, Qt::LeftButton, 0, downButton ); QCOMPARE( spinBox.value(), 1 ); }

By single-stepping through the code in Visual Studio while running the SQL Profiler, we can see that nothing appears in the profiler until we start to execute the foreach loop, at which point the profiler shows an Audit Login message, indicating that our program has opened a connection to the database. This is followed by a

this message, the profiler shows the SQL that the EF just ran for us:

exec sp_executesql N'SELECT [Extent1].[SalesOrderID] AS [SalesOrderID], [Extent1].[RevisionNumber] AS [RevisionNumber], [Extent1].[OrderDate] AS [OrderDate], [Extent1].[DueDate] AS [DueDate], [Extent1].[ShipDate] AS [ShipDate], [Extent1].[Status] AS [Status], [Extent1].[OnlineOrderFlag] AS [OnlineOrderFlag], [Extent1].[SalesOrderNumber] AS [SalesOrderNumber], [Extent1].[PurchaseOrderNumber] AS [PurchaseOrderNumber], [Extent1].[AccountNumber] AS [AccountNumber], [Extent1].[CustomerID] AS [CustomerID], [Extent1].[ShipToAddressID] AS [ShipToAddressID], [Extent1].[BillToAddressID] AS [BillToAddressID], [Extent1].[ShipMethod] AS [ShipMethod], [Extent1].[CreditCardApprovalCode] AS [CreditCardApprovalCode], [Extent1].[SubTotal] AS [SubTotal], [Extent1].[TaxAmt] AS [TaxAmt], [Extent1].[Freight] AS [Freight], [Extent1].[TotalDue] AS [TotalDue], [Extent1].[Comment] AS [Comment], [Extent1].[rowguid] AS [rowguid], [Extent1].[ModifiedDate] AS [ModifiedDate] FROM [SalesLT].[SalesOrderHeader] AS [Extent1] WHERE [Extent1].[OrderDate] = @p__linq__0', N'@p__linq__0 datetime',@p__linq__0='2004-06-01 00:00:00'

focus() scrollIntoView() removeCSSClass(String className) toggleCSSClass(String className)

It might be quite long, but structurally that s a pretty simple SELECT statement. The only reason it s so large is that it explicitly requests every column required by the entity (and it has specified each column in a fairly verbose manner). The interesting part is in the last two lines. The penultimate line is a parameterized WHERE clause comparing the OrderDate to a named argument. This is what became of our LINQ query s where clause. And the final line provides a value for that named argument. Note that you re free to chain operators together in LINQ to Entities just as you can in LINQ to Objects. For example, we could build on the orders query from Example 14-3: