knowledge: How to Create Durable Service

Let us understand more about the durable service by creating Simple Calculator service which persist the instance state in SQL server database.

Step 1: Start the Visual Studio 2008 and click File->New->Web Site. Select the 'WCF Service' as shown below.

Step 2: Create interface and decorate with Service and Operation contract.

    [ServiceContract()]
    public interface ISimpleCalculator
    {
        [OperationContract]
        int Add(int num);

        [OperationContract]
        int Subtract(int num);

        [OperationContract]
        int Multiply(int num);

        [OperationContract]
        void EndPersistence();
    }

Step 3: You need to add [Serializable] And [DurableService()] attribute to the service implementation. Set CanCreateInstance = true property to the operation in which instance state has to be persisted and set CompletesInstance = true when state has to be destroyed. In this implementation, we are going to persist the 'currentValue' variable value to the database.

using System.Runtime.Serialization;
using System.ServiceModel;
using System.Text;
using System.ServiceModel.Description;
    [Serializable]
    [DurableService()]
    public class SimpleCalculator :ISimpleCalculator 
    {
        int currentValue = default(int);
        [DurableOperation(CanCreateInstance = true)]
        public int Add(int num)
        {
            return (currentValue += num);
        }
        [DurableOperation()]
        public int Subtract(int num)
        {
            return (currentValue -= num);
        }
        [DurableOperation()]
        public int Multiply(int num)
        {
            return (currentValue *= num);
        }
        [DurableOperation(CompletesInstance = true)]
        public void EndPersistence()
        {
        }

Step 4: Before configuring the database information in the durable service, you need to set up DataStore environment. Microsoft provides inbuilt sqlPersistance provider. To set up the database environment, run the these sql query located at following location 'C:\Windows\Microsoft.NET\Framework\v3.5\SQL\EN'

SqlPersistenceProviderSchema.sql
SqlPersistenceProviderLogic.sql

Step 5: In order to support durable service, you need to use Context binding type. <persistenceProvider> tag is used to configure the persistence provider.

<system.serviceModel>
 <services>
  <service name="SimpleCalculator" behaviorConfiguration="ServiceBehavior">
  <!-- Service Endpoints -->
  <endpoint address="" binding="wsHttpContextBinding" 
  bindingConfiguration="browConfig" contract="ISimpleCalculator">
  <identity>
  <dns value="localhost"/>
  </identity>
  </endpoint>
  <endpoint address="mex" binding="mexHttpBinding" 
  contract="IMetadataExchange"/>
  </service>
 </services>
 <behaviors>
  <serviceBehaviors>
  <behavior name="ServiceBehavior">
  <serviceMetadata httpGetEnabled="true"/>
 <serviceDebug includeExceptionDetailInFaults="true"/>
    <persistenceProvider  
     type="System.ServiceModel.Persistence.SqlPersistenceProviderFactory,
        System.WorkflowServices, Version=3.5.0.0, Culture=neutral,
         PublicKeyToken=31bf3856ad364e35" connectionStringName="DurableServiceStore" 
                               persistenceOperationTimeout="00:00:10"
                               lockTimeout="00:01:00"
                               serializeAsText="true"/>
   </behavior>
   </serviceBehaviors>
  </behaviors>
    <bindings>
      <wsHttpContextBinding >
        <binding name="browConfig" >
          <security mode="None"></security>
        </binding>
      </wsHttpContextBinding>
    </bindings>
</system.serviceModel>
<connectionStrings>
<add name="DurableServiceStore" 
connectionString="Data Source=saravanakumar;Initial Catalog
=DurableServiceStore;Integrated Security=True"/>
</connectionStrings>

Step 6: Create the console client application and name it as DurableServiceClient

Step 7: Add following reference to client application

System.ServiceModel
System.WorkflowService

Step 8: Add WCF service as Service Reference to the project and name it as SimpleCalculatorService

Step 9: Create the Helper class called it as Helper.cs. This helper class is used to Store, Retrieve and set the context at the client side. Context information will be saved in 'token_context.bin' file. Copy and paste the below code to your helper file.
Helper.cs

using System.ServiceModel.Channels;
using System.ServiceModel;
using System.Net;
using System.IO;
using System.Runtime.Serialization.Formatters.Binary;

    public class Helper
    {
        static readonly String TokenContextFileName = "token_context.bin";

        public static IDictionary<String, String> LoadContext()
        {
            IDictionary<String, String> ctx = null;

            try
            {
                using (FileStream fs = new 
                FileStream(TokenContextFileName, FileMode.Open, FileAccess.Read))
                {
                    BinaryFormatter bf = new BinaryFormatter();

                    ctx = bf.Deserialize(fs) as IDictionary<String, String>;

                    fs.Close();
                }
            }
            catch (Exception ex)
            {

            }
            return ctx;
        }

        public static void SaveContext(IClientChannel channel)
        {
            IDictionary<String, String> ctx = null;
            IContextManager cm = channel.GetProperty<IContextManager>();
            if (cm != null)
            {
                ctx = cm.GetContext() as IDictionary<String, String>;
                try
                {
                    using (FileStream fs 
                    = new FileStream(TokenContextFileName, FileMode.CreateNew))
                    {
                        BinaryFormatter bf = new BinaryFormatter();

                        bf.Serialize(fs, ctx);

                        fs.Close();
                    }
                }
                catch (Exception ex)
                {

                }
            }
        }

        public static void DeleteContext()
        {
            try
            {
                File.Delete(TokenContextFileName);
            }
            catch (Exception ex)
            {
            }
        }

        public static void SetContext(IClientChannel channel,
         IDictionary<String, String> ctx)
        {
            IContextManager cm = channel.GetProperty<IContextManager>();
            if (cm != null)
            {
                cm.SetContext(ctx);
            }
        }
    }

Step 10: In the main method, I was creating the proxy for the service and calling the Add operation. Call to this method will add instance state to the database. Now I have closed the proxy and creating new proxy instance. When I call the Subtract and Multiply operation, it will operate on the previously saved value (instance state).

static void Main(string[] args)
        {
           
             //Create the proxy for the service
            SimpleCalculatorService.SimpleCalculatorClient client 
            = new SimpleCalculatorService.SimpleCalculatorClient
            "WSHttpContextBinding_ISimpleCalculator");
            int currentValue = 0;
            //Call the Add method from the service
            currentValue = client.Add(10000);     
            Console.WriteLine("The current value is {0}", currentValue);
            //Save the Context from the service to the client
           Helper.SaveContext(client.InnerChannel); 
            //Close the proxy
            client.Close();
            
            //Create new Instance of the proxy for the service
            client = new SimpleCalculatorService.SimpleCalculatorClient
            ("WSHttpContextBinding_ISimpleCalculator");
            //Load the context from the client to start from saved state
            IDictionary<string,string> cntx=Helper.LoadContext();
            //Set Context to context manager
            Helper.SetContext(client.InnerChannel, cntx);
            //Call the Subtract and Multiply method from service
            currentValue = client.Subtract(2);
            Console.WriteLine("The current value is {0}", currentValue);
            currentValue = client.Multiply(5);
            Console.WriteLine("The current value is {0}", currentValue);
            //Delete the context from the client
            Helper.DeleteContext();
            //Remove persistance state from the server
            client.EndPersistence();
            Console.WriteLine("Press <ENTER> to shut down the client.");
            Console.ReadLine();
            client.Close();

        }

End of the proxy 1, service instance saved in the database as shown below.