MSDN Magazine - December 2008 - (Page 73)

change tracking to the communications protocol. Another approach, and the one I am advocating here, is to make change state part of the data contract for each entity: [DataContract] public enum TrackingInfo { [EnumMember] Unchanged, [EnumMember] Created, [EnumMember] Updated, [EnumMember] Deleted } OrderService Data Access Layer Client ChangeTrackingCollection Data Transfer Objects - Customer - Product - Order - OrderDetail IDataProvider: - GetOrder, CreateOrder, UpdateOrder, DeleteOrder SqlDataProvider: IDataProvider - LINQ to SQL EntityDataProvider: IDataProvider - Entity Framework In addition to other properties, each DTO would have a TrackingState property using the TrackingInfo enum. All that’s required Northwind Database is for both sides to agree on this data contract. Even though I’ve added a Track- Figure 1 Service-Oriented Architecture for an Order Processing App ingState property to each DTO, I must still rely on the client, which has no knowledge of LINQ to be tempted to use them in your service operations anyway, despite SQL or the Entity Framework, to track which objects have been the extra baggage they carry. After all, collection types such as those created, updated or deleted and to set the TrackingState property used by LINQ to SQL and the Entity Framework show up as simple to the corresponding value (see Figure 1). I’ve crafted a generic arrays on the client when you set a WCF service reference. change-tracking collection to perform this task. There are two types Consider, however, that when you set the SerializationMode of of the collection, one that extends ObservableCollection for the LINQ to SQL DataContext from None to Unidirectional, only Windows Presentation Foundation (WPF) applications, and an- the “many” side of one-to-many relations will be marked with the other that extends BindingList for use with Windows Forms DataMember attribute. This means that if you have an Order entity applications. Each caches deleted items before removing them from with Customer and Order_Details properties, Order_Details will the collection and has a GetChanges method which returns only be marked with DataMember and included in the data contract, items that have been inserted, updated, or deleted. but Customer will not. The Entity Framework, on the other hand, will include more fields than you may want in the data contract, Creating the Data Access Layer The DAL helps insulate other parts of the application from the details of object persistence. For this reason, it is important that objects exposed through the DAL exclude remnants of any specific data access technology. Both LINQ to SQL and the Entity Framework allow you to manufacture entities using both command-line tools and Visual Studio designers; however, these code-generated entities possess some artifacts that betray their origins. LINQ to SQL, for example, represents data relations using the EntityRef and EntitySet collection types in order to support deferred loading of associated objects, while the Entity Framework represents navigation properties using EntityReference and EntityCollection . Likewise, these entities incorporate code elements intended to support client-server scenarios, such as validation (using partial methods) and data binding (with INotifyPropertyChanged), which are unnecessary when you only use them for communication with a Windows Communication Foundation (WCF) service. Because both LINQ to SQL and the Entity Framework support serialization of entities using the DataContractSerializer (by marking them with DataContract and DataMember attributes), you may msdnmagazine.com Figure 2 DTO Representing an Order from Northwind namespace DataTransferObjects { [DataContract] public class Order { [DataMember] public int OrderID { get; set; } [DataMember] public string CustomerID { get; set; } [DataMember] public string CustomerName { get; set; } [DataMember] public DateTime? OrderDate { get; set; } [DataMember] public List OrderDetails { get; set; } [DataMember] public byte[] Updated { get; set; } [DataMember] public TrackingInfo TrackingState { get; set; } } } December 2008 73 http://www.msdnmagazine.com

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

MSDN Magazine - December 2008 Contents Toolbox CLR Inside Out Advanced Basics Cutting Edge Patterns In Practice Team System Real-World WF Visual Studio OBA Tools SOA Data Access Geneva Framework Test Run Foundations Windows With C++ Going Places End Bracket

MSDN Magazine - December 2008

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