Archive for the ‘Active Record’ Category.

ActiveRecord Session Scope and WCF Redux

Awhile ago, I posted a solution I was using for a project for managing SessionScope with WCF using an ICallContextInitializer. Because of another issue in the codebase (an error in a custom listener), an exception was getting thrown when session.Dispose() was called in the AfterInvoke method.  What was interesting was that it appeared to the client that the WCF call had completed successfully — even though this was not the case.  It turns out that ICallContextInitializer is not the best WCF extension to use to manage the scope. Here’s a quick console application that will show the behavior of throwing an exception in AfterInvoke. Notice how the console window will crash before the ReadKey is hit:  

 

   1: class Program
   2: {
   3:     static void Main(string[] args)
   4:     {
   5:         using (var host = new ServiceHost(typeof(Operation)))
   6:         {
   7:             var endpointAddress = new EndpointAddress("net.tcp://localhost/optest");
   8:             var endpoint = new ServiceEndpoint(ContractDescription.GetContract(typeof(IOperation)),
   9:                                                new NetTcpBinding(),
  10:                                                endpointAddress);
  11:             endpoint.Behaviors.Add(new ThrowBehavior());
  12:             host.Description.Endpoints.Add(endpoint);
  13:             host.Open();
  14:  
  15:             var op = ChannelFactory<IOperation>.CreateChannel(new NetTcpBinding(), endpointAddress);
  16:             op.Op();
  17:         }
  18:  
  19:         Console.ReadKey();
  20:     }
  21: }
  22:  
  23:
 [ServiceContract]
  24: public interface IOperation
  25: {
  26:     [OperationContract]
  27:     void Op();
  28: }
  29:  
  30: public class Operation : IOperation
  31: {
  32:     public void Op()
  33:     {
  34:     } 
  35: }
  36:  
  37: internal class ThrowBehavior : IEndpointBehavior
  38: {
  39:     public void Validate(ServiceEndpoint endpoint)
  40:     {
  41:     }
  42:  
  43:     public void AddBindingParameters(ServiceEndpoint endpoint, BindingParameterCollection bindingParameters)
  44:     {
  45:     }
  46:  
  47:     public void Apply
DispatchBehavior(ServiceEndpoint endpoint, EndpointDispatcher endpointDispatcher)
  48:     {
  49:         foreach (DispatchOperation operation in endpointDispatcher.DispatchRuntime.Operations)
  50:         {
  51:             operation.CallContextInitializers.Add(new ThrowCallContextInitializer());
  52:         }
  53:     }
  54:  
  55:     public void ApplyClientBehavior(ServiceEndpoint endpoint, ClientRuntime clientRuntime)
  56:     {
  57:     }
  58: }
  59:  
  60: internal class ThrowCallContextInitializer : ICallContextInitializer
  61: {
  62:     public object BeforeInvoke(InstanceContext instanceContext, IClientChannel channel, Message message)
  63:     {
  64:         return null;
  65:     }
  66:  
  67:     public void AfterInvoke(object correlationState)
  68:     {
  69:         throw new InvalidOperationException();

  70:     }
  71: }

 

My revised code uses a DispatchMessageInterceptor instead:

 

   1: public class ARSessionScopeBehavior : IEndpointBehavior
   2: {
   3:     
   4:     /// <summary>
   5:     /// Implement to pass data at runtime to bindings to support custom behavior.
   6:     /// </summary>
   7:     /// <param name="endpoint">The endpoint to modify.</param>
   8:     /// <param name="bindingParameters">The objects that binding elements require to support the behavior.</param>
   9:     public void AddBindingParameters(ServiceEndpoint endpoint, BindingParameterCollection bindingParameters)
  10:     {
  11:     }
  12:  
  13:     /// <summary>
  14:     /// Implements a modification or extension of the service across an endpoint.
  15:     /// </summary>
  16:     /// <param name="endpoint">The endpoint that exposes the contract.</param>
  17:     /// <param name="endpointDispatcher">The endpoint dispatcher to be modified or extended.</param>
  18:     public void ApplyDispatchBehavior(ServiceEndpoint endpoint, EndpointDispatcher endpointDispatcher)
  19:     {
  20:         endpointDispatcher.DispatchRuntime.MessageInspectors.Add(new ARDispatcherMessageInspector());
  21:     }
  22:  
  23:     /// <summary>
  24:     /// Implements a modification or extension of the client across an endpoint.
  25:     /// </summary>
  26:     /// <param name="endpoint">The endpoint that is to be customized.</param>
  27:     /// <param name="clientRuntime">The client runtime to be customized.</param>
  28:     public void ApplyClientBehavior(ServiceEndpoint endpoint, ClientRuntime clientRuntime)
  29:     {
  30:     }
  31:  
  32:     /// <summary>
  33:     /// Implement to confirm that the endpoint meets some intended criteria.
  34:     /// </summary>
  35:     /// <param name="endpoint">The endpoint to validate.</param>
  36:     public void Validate(ServiceEndpoint endpoint)
  37:     {
  38:     }
  39:  
  40: }

 

   1: public class ARDispatchMessageInspector : IDispatchMessageInspector
   2:  {
   3:  
   4:      private static readonly ILogger Logger = LogManager.GetLogger(ARDispatchMessageInspector);
   5:  
   6:      private const string ActiveRecordSessionScopeKey = "wcf.ar.sessionscope";
   7:  
   8:      #region Implementation of IDispatchMessageInspector
   9:  
  10:      /// <summary>
  11:      /// Called after an inbound message has been received but before the message is dispatched to the intended operation.
  12:      /// </summary>
  13:      /// <returns>
  14:      /// The object used to correlate state. This object is passed back in the <see cref="M:System.ServiceModel.Dispatcher.IDispatchMessageInspector.BeforeSendReply(System.ServiceModel.Channels.Message@,System.Object)" /> method.
  15:      /// </returns>
  16:      /// <param name="request">The request message.</param>
  17:      /// <param name="channel">The incoming channel.</param>
  18:      /// <param name="instanceContext">The current service instance.</param>
  19:      public object AfterReceiveRequest(ref Message request, IClientChannel channel, InstanceContext instanceContext)
  20:      {
  21:          var scope = Local.Data[ActiveRecordSessionScopeKey] as SessionScope;
  22:          if (scope == null)
  23:          {
  24:              Logger.Debug("Creating new ActiveRecord SessonScope");
  25:              scope = new SessionScope();
  26:              Local.Data[ActiveRecordSessionScopeKey] = scope;
  27:          }
  28:          return null;
  29:      }
  30:  
  31:      /// <summary>
  32:      /// Called after the operation has returned but before the reply message is sent.
  33:      /// </summary>
  34:      /// <param name="reply">The reply message. This value is null if the operation is one way.</param>
  35:      /// <param name="correlationState">The correlation object returned from the <see cref="M:System.ServiceModel.Dispatcher.IDispatchMessageInspector.AfterReceiveRequest(System.ServiceModel.Channels.Message@,System.ServiceModel.IClientChannel,System.ServiceModel.InstanceContext)" /> method.</param>
  36:      public void BeforeSendReply(ref Message reply, object correlationState)
  37:      {
  38:          var scope = Local.Data[ActiveRecordSessionScopeKey] as SessionScope;
  39:          if (scope != null)
  40:          {
  41:              if (SessionScope.Current == scope)
  42:              {
  43:                  Logger.Debug("Disposing ActiveRecord SessonScope");
  44:                  scope.Dispose();
  45:              }
  46:              else
  47:              {
  48:                  Logger.Warn(
  49:                      "The current Active Record session scope does not equal the correlated session scope from WCF.  This scope will not " +
  50:                      "be disposed, however, this could lead to entities not being properly flushed.");
  51:              }
  52:              Local.Data[ActiveRecordSessionScopeKey] = null;
  53:          }
  54:      }

 

So far, no problems.  Funny enough, when searching for solutions to this problem, I noticed some other posts where people recommended using the ICallContextInitializer to manage unit of work.  I assume they just have not had any issues when calling Dispose() and have not seen this behavior.

Advanced ActiveRecord Models - Part 2

In part 1, I discussed what Castle ActiveRecord does when starting up and ways you can modify the model after is has been generated.  Another useful trick is to add custom attributes to your model that can be inspected while ActiveRecord is inspecting its model.  To this you need to create a class that implements Castle.ActiveRecord.Framework.Internal.IModelBuilderExtension and register it with the ActiveRecordStarter.

 

For my example, let’s assume that we want to implement soft deletes using ActiveRecord.  The NHibernate FAQ has a great blog entry on how to make NHibernate mark a entity as deleted as opposed to deleting it from the database.  Assuming you are using their model of marking your entities as ISoftDeleteable, here are two things we can do to extend this model:

 

  1. If session.Get(id) is called on soft deleted record, null is returned.
  2. If a collection contains a record that has been soft deleted, that record will not show up when the collection is loaded.

 

I am not entirely sure that these two features are something that you want to necessarily do, however, they are good examples for what I am trying to show.  The reason I say that is because I am not sure you want entities showing up sometimes and not other times, i.e. a soft deleted model would show up for a custom query unless someone checks the Deleted flag, how do soft deletes work across entity graphs, should we allow both ends of a bidirectional relationship to be soft deleteable, etc.  So, I have kept this example limited too two easy features, but remember to think about this a little more before actually implementing it.  So on to the example, the first thing we need to is to add a custom model builder to inspect our model:

 

   1: public class SoftDeleteModelBuilderExtension : IModelBuilderExtension
   2: {
   3:  
   4:     public static IDictionary<Type, SoftDeleteModel> SoftDeleteModels = new Dictionary<Type, SoftDeleteModel>();
   5:  
   6:     #region IModelBuilderExtension Members
   7:  
   8:     public void ProcessBelongsTo(System.Reflection.PropertyInfo pi, BelongsToModel belongsToModel, ActiveRecordModel model)
   9:     {
  10:     }
  11:  
  12:     public void ProcessClass(Type type, ActiveRecordModel model)
  13:     {
  14:         GetModel(type, model);
  15:     }
  16:  
  17:     public void ProcessField(System.Reflection.FieldInfo fi, ActiveRecordModel model)
  18:     {
  19:     }
  20:  
  21:     public void ProcessHasAndBelongsToMany(System.Reflection.PropertyInfo pi, HasAndBelongsToManyModel hasAndBelongManyModel, ActiveRecordModel model)
  22:     {
  23:         if (!IsSoftModel(hasAndBelongManyModel.HasManyAtt.MapType)) return;
  24:         var softDeleteModel = GetModel(model.Type, model);
  25:         softDeleteModel.HasAndBelongsToMany.Add(hasAndBelongManyModel);
  26:     }
  27:  
  28:     public void ProcessHasMany(System.Reflection.PropertyInfo pi, HasManyModel hasManyModel, ActiveRecordModel model)
  29:     {
  30:         if (!IsSoftModel(hasManyModel.HasManyAtt.MapType)) return;
  31:         var softDeleteModel = GetModel(model.Type, model);
  32:         softDeleteModel.HasMany.Add(hasManyModel);
  33:     }
  34:  
  35:     public void ProcessHasManyToAny(System.Reflection.PropertyInfo pi, HasManyToAnyModel hasManyModel, ActiveRecordModel model)
  36:     {
  37:         if (!IsSoftModel(hasManyModel.HasManyToAnyAtt.MapType)) return;
  38:         var softDeleteModel = GetModel(model.Type, model);
  39:         softDeleteModel.ManyToAny.Add(hasManyModel);
  40:     }
  41:  
  42:     public void ProcessProperty(System.Reflection.PropertyInfo pi, ActiveRecordModel model)
  43:     {
  44:     }
  45:  
  46:     private static bool IsSoftModel(Type type)
  47:     {
  48:         return (typeof(ISoftDeleteable).IsAssignableFrom(type));
  49:     }
  50:  
  51:     private static SoftDeleteModel GetModel(Type type, ActiveRecordModel model)
  52:     {
  53:         SoftDeleteModel softDeleteModel;
  54:         SoftDeleteModels.TryGetValue(type, out softDeleteModel);
  55:  
  56:         if (softDeleteModel == null)
  57:         {
  58:             softDeleteModel = new SoftDeleteModel {Type = type, ActiveRecordModel = model};
  59:             if (IsSoftModel(type))
  60:                 softDeleteModel.SoftDeleteable = true;
  61:             SoftDeleteModels[type] = softDeleteModel;
  62:         }
  63:         return softDeleteModel;
  64:     }
  65:  
  66:     #endregion
  67: }

 

   1: public class SoftDeleteModel
   2: {
   3:     /// <summary>
   4:     /// Gets or sets the type.
   5:     /// </summary>
   6:     /// <value>The type.</value>
   7:     public Type Type { get; set; }
   8:  
   9:     /// <summary>
  10:     /// Gets or sets a value indicating whether the model is soft deleteable.
  11:     /// </summary>
  12:     /// <value><c>true</c> if soft deleteable; otherwise, <c>false</c>.</value>
  13:     public bool SoftDeleteable { get; set; }
  14:  
  15:     /// <summary>
  16:     /// Gets or sets the active record model for this type.
  17:     /// </summary>
  18:     /// <value>The active record model.</value>
  19:     public ActiveRecordModel ActiveRecordModel { get; set; }
  20:  
  21:     private readonly HashSet<HasManyModel> _hasMany = new HashSet<HasManyModel>();
  22:  
  23:     /// <summary>
  24:     /// Gets the has many relationships to a soft deleted type.
  25:     /// </summary>
  26:     /// <value>The has many.</value>
  27:     public HashSet<HasManyModel> HasMany
  28:     {
  29:         get { return _hasMany; }
  30:     }
  31:  
  32:     private readonly HashSet<HasAndBelongsToManyModel> _hasAndBelongsToMany = new HashSet<HasAndBelongsToManyModel>();
  33: