MSDN Magazine - July 2008 - (Page 33)

open and you want to use optimistic concurrency, you can do so by setting the ConcurrencyMode attribute of the EntityType in the conceptual model. Editing the EDM file and setting the ConcurrencyMode to Fixed tells the Entity Framework to add this column to the WHERE clause of any Update or Delete commands. Thus, an OptimisticConcurrencyException is raised if a matching row is not found. Figure 7 shows this exception being raised when I modified the region of a customer in the database, just before the user tried to modify the same region. You can trap this exception and take whatever action is appropriate. For example, you could trap the exception, log it, and then overwrite the user’s changes anyway, as shown here: catch (OptimisticConcurrencyException e){ context.Refresh(RefreshMode.ClientWins, customer); // Last in wins logger.Write(e); context.SaveChanges(); } Guerrilla .NET: The Essentials C# & The .NET Platform July 28th-August 1st Los Angeles Call 800.699.1932 to register today! or visit www.develop.com New Hands-on .NET 3.0/3.5 Training What’s New in .NET 3.0-3.5 w/LINQ July 21st - Boston When a user deletes a customer, the CustomerManager’s DeleteCustomer method gets the customer entity and applies the delete: context.Attach(customer); context.DeleteObject(customer); context.SaveChanges(); Windows Communication Foundation w/ 3.5 content July 7th - Boston July 21st - Bellevue. WA August 4th - Los Angeles First, the Customer entity instance must be reunited with an ObjectContext using the Attach method. Then the customer must be deleted from the ObjectContext. Done this way, the change tracking mechanism within the ObjectContext is aware the Customer entity instance has been deleted. Finally, when the SaveChanges method is called, the ObjectContext is now aware the entity was deleted and it should generate a DELETE SQL command and execute it. When adding a customer, the CustomerManager’s AddCustomer method gets the customer entity and applies the insert, like so: context.AddToCustomers(customer); context.SaveChanges(); Windows Presentation Foundation w/ 3.5 content July 14th - Boston July 28th - Chicago August 11th - Los Angeles Windows WorkFlow Foundation August 4th - Los Angeles NEW COURSE What’s New in SQL Server 2008 August 25th - Los Angeles This entity instance is new, so it must be added to the context and flagged as a new instance of a Customer entity by associating the Customer entity instance with an ObjectContext using the AddToCustomer method. Finally, when the SaveChanges method is called, the ObjectContext is aware that the entity was added and that it should generate an INSERT SQL command and execute it. On-Site Training For groups of students, DevelopMentor’s On-Site course delivery may offer the most cost-effective solution – at your location, at the time you need it. OnSites also offer the ability to customize a course to your group’s needs, including course content, labs that run on your programming platform and lab exercises tailored to your business or project. Call us today to discuss your training needs! US -800.699.1932 UK -(0)8000.562.265 Europe-(0)01242.525.108 Here I’ve demonstrated how the Entity Framework can integrate into an architecture, use modern patterns such as the MVP pattern, and handle the common architectural concerns. Key components of the Entity Framework in layered architectures are its change tracking mechanisms, integration with LINQ to Entities, ability to disconnect and reconnect with its ObjectContext, and how it provides a means for a developer to handle concurrency issues. JOHN PAPA (johnpapa.net) is a Senior Consultant with ASPSOFT (aspsoft.com) and a baseball fan who spends summer nights rooting for the Yankees with his family. John, a C# MVP and INETA speaker, has authored several books and is now working on his latest, titled Data Access with Silverlight 2. He often speaks at conferences such as DevConnections and VSLive. msdnmagazine.com July 2008 33 http://www.develop.com http://www.develop.com http://johnpapa.net http://aspsoft.com http://msdnmagazine.com

Table of Contents Feed for the Digital Edition of MSDN Magazine - July 2008

MSDN Magazine - July 2008 Contents Toolbox CLR Inside Out Flex Your Data Data Points Advanced Basics Office Space Cutting Edge Data Services ADO.NET Data and WPF Transactions WCF P2P Test Run Security Briefs Foundations .NET Matters {End Bracket}

MSDN Magazine - July 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.