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

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.

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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.

The decision to choose a different view engine is still quite important, because it has long-term technical and nontechnical ramifications. Alternative view engines should be another option to investigate for MVC applications, because they offer compelling alternatives to the default WebFormViewEngine.

Doing more with Skinr . ................................................................................................ 195 Using PHP and template files ........................................................................................ 196 Summary . .................................................................................................................... 199

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:

10.4 Summary

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'

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:

var orderedOrders = orders.OrderBy(order => order.OrderDate);

With the release of ASP.NET MVC 2 came several more options for organizing content in our views. Child actions moved from the MVC Futures assembly to being first-class citizens, and the addition of templates has allowed us to build standardized content in our views. With master pages, partials, child actions, templates, and HtmlHelper extensions, we have many options for rendering our views beyond just a single page. Each has its sweet spot, and we can be assured that any duplication we encounter in our views can be easily addressed. The only question is how we want to address it. A querystring parameter builder is one of these ways. Because of the extensibility of ASP.NET MVC, we can also swap out our view engine without affecting our controllers. The Spark view engine, optimized for code in markup, is a viable alternative to some of the ugliness that comes with mixing C# and markup in the traditional Web Forms view engine. In the next chapter, we ll take a look at securing our MVC applications.

9: Designing for a Browser . ..................................................................... 201

var orderedOrders = from order in orders orderby order.OrderDate select order;

This doesn t execute the orders query. It just means we have two queries now the orders query that just filters, and then the orderedOrders query that filters and then sorts. You could think of this chained query as shorthand for Example 14-11, which explicitly combines the clauses from Example 14-9 and Example 14-10 into one query.

Requiring authentication and authorization Preventing cross-site scripting attacks Mitigating cross-site request forgeries Avoiding JSON hijacking

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