barcodelib c# Managing Concurrency When Disconnected in Font

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9-2. Managing Concurrency When Disconnected
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You want to make sure that changes made on an entity by a WCF client are applied only if the concurrency token has not changed.
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Let s suppose you have a model like the one in Figure 9-2.
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Figure 9-2. Our model with a single Order entity
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USING THE ENTITY FRAMEWORK IN N-TIER APPLICATIONS
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We want to update an order using a WCF service while guaranteeing that the order we re updating has not changed since the last time we retrieved the order. We ll show two slightly different ways to handle this. In both approaches we use a concurrency column, in our case, the TimeStamp column. 1. 2. Create a WCF Service Library by right-clicking the solution and selecting Add New Project. Select WCF WCF Service Library. Right-click the project and select Add New Item. Select Data ADO.NET Entity Data Model. Use the wizard to add a model with the Order table. Rightclick the TimeStamp property, select Properties and set its Concurrency Mode to Fixed. Because the default entities generated by Entity Framework can t be serialized, we ll need to create our own entities using POCO. With the Entity Data Model Designer open, view the properties window and change the Code Generation Strategy to None. Next, add the code in Listing 9-5 to create the POCO class for the Order entity and our object context. In the IService1.cs file, change the service definition as shown in Listing 9-6. In the Service1.cs file, implement the service as shown in Listing 9-7. To test our service, we ll need a client. Add a new Windows Console Application project to the solution. Use the code in Listing 9-8 for the client. Add a service reference to the client by right-clicking the client project and selecting Add Service Reference. You may need to right-click the service project and select Debug Start Instance to start an instance of your service before you can add a service reference in the client.
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4. 5. 6.
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Listing 9-5. The code for the Order POCO class and the related object context public class Order { public int OrderId { get; set; } public string Product { get; set; } public int Quantity { get; set; } public string Status { get; set; } public byte[] TimeStamp { get; set; } } public class EFRecipesEntities : ObjectContext { public EFRecipesEntities() : base("name=EFRecipesEntities", "EFRecipesEntities") { } private IObjectSet<Order> orders; public IObjectSet<Order> Orders { get { return orders (orders = CreateObjectSet<Order>()); } } }
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USING THE ENTITY FRAMEWORK IN N-TIER APPLICATIONS
Listing 9-6. Our WCF service contract [ServiceContract] public interface IService1 { [OperationContract] Order InsertOrder(); [OperationContract] void UpdateOrderWithoutRetrieving(Order order); [OperationContract] void UpdateOrderByRetrieving(Order order); } Listing 9-7. The implementation of our service contract public class Service1 : IService1 { public Order InsertOrder() { using (var context = new EFRecipesEntities()) { // remove previous test data context.ExecuteStoreCommand("delete from chapter9.[order]"); var order = new Order { Product = "Camping Tent", Quantity = 3, Status = "Received" }; context.Orders.AddObject(order); context.SaveChanges(); return order; } } public void UpdateOrderWithoutRetrieving(Order order) { using (var context = new EFRecipesEntities()) { context.Orders.Attach(order); if (order.Status == "Received") { var entry = context.ObjectStateManager .GetObjectStateEntry(order); entry.SetModifiedProperty("Quantity"); context.SaveChanges(); } } } public void UpdateOrderByRetrieving(Order order) {
USING THE ENTITY FRAMEWORK IN N-TIER APPLICATIONS
using (var context = new EFRecipesEntities()) { var dbOrder = context.Orders .Single(o => o.OrderId == order.OrderId); if (dbOrder != null && StructuralComparisons.StructuralEqualityComparer .Equals(order.TimeStamp, dbOrder.TimeStamp)) { dbOrder.Quantity = order.Quantity; context.SaveChanges(); } } } } Listing 9-8. The client we use to test our WCF service class Program { static void Main(string[] args) { var service = new Service1Client(); var order = service.InsertOrder(); order.Quantity = 5; service.UpdateOrderWithoutRetrieving(order); order = service.InsertOrder(); order.Quantity = 3; service.UpdateOrderByRetrieving(order); } } If you set a breakpoint on the first line in the Main() method of the client and debug the application, you can step through the inserting the order and updating the order using both methods.
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