I am using Wcf in Sharp Architecture. I have configured my project following northwind sample using WcfSessionStorage etc. I have a method in the wcf service that gets a list of business object using Repository<>.GetAll(). I am testing the service method using WcfTestClient. When the method is called the very first time, everything works fine. However on the subsequent call, I get the following exception on the Repository<>.GetAll() method
[System.ObjectDisposedException]
Session is closed!
Object name: 'ISession'
It seems like the NHibernate session gets disposed after each call. I have got around this problem by decorating my service with the following attribute
[ServiceBehavior( InstanceContextMode = InstanceContextMode.PerCall )]
public class WcfService : IWcfService
{
}
However this means, an instance of the service will be created on each call that in turn will create a new nhibernate session etc. In my scenario there is no need of creating a new service instance per call and I think its an expensive process and not the right solution. I would like to know what is the best practice in my scenario and how to get this thing work with creating a new service instace per call.
Thanks
Nabeel
The easiest way is to create a new instance every time and it's not an expensive process, because creating a new object in .NET is like 0.00000000000000001 second (I read that on Ayande's blog or somewhere).
I use Autofac DI in my projects and I usually make ISession as container scoped (one per request). And then every class that uses (directly or indirectly) ISession has to be container scoped or lower (factory scoped == every class usage get's a new instance). If a class that uses ISession is higer scoped (session scoped == singleton) you'll run into problems that you currently have.
If your service is singleton service:
At first run the service is created, this service uses ISession, which should be container scoped, and it is on the first run.
The next request to service (service is now created) has still a reference to created ISession (which was closed on previous end request), so now it's closed.
I don't recomend using the same ISession that you'll open/close (it's not recomended in the NHibernate documentation), just use container scoped (I do and I don't have any performance issues), or you should create ISession manually in every method in your service like:
using(ISession s = ISessionFactory.OpenSession())
using(ITransaction t = .....)
....
But that isn't nice at all...
Please take a look at my answer to my own similar question: WCF/S#arpArch: underlying ISession is closed after the first call within a request.
#dmonlord is right that the creation of additional session instances within the same request is very cheap in this case.
Related
I am using DryIoc (last release version) for Dependency Injection.
In my application (Asp.net Core 3.1), I am using Entity Framework.
My AppDbContext hinerits DbContext and implements IDisposable
I also use UnitOfWork pattern and the class is disposable.
These two objects are declared as Transient.
I follow the documentation of DryIoc that explains the context with Transient Disposable objects:
https://github.com/dadhi/DryIoc/blob/master/docs/DryIoc.Docs/ReuseAndScopes.md
For my AppDbContext, I resolve this service manually. Same thing for my UnitOfWork. At the end I call Dispose method.
But these two instances are not destroyed and are stored in the Singleton Scope of the DryIoc Container.
I did some tests and use JetBrain dotMemory.
My test is to call 100 times a method
Call controler
open UnitOfWork
create AppDbContext
call database to get my data
close / dispose objects.
At the end, I have 100 times my AppDbContext and my UnitOfWork in the scope of the container:
I tried a lot of combinations of creation of container but each time, it is the same thing:
var container = new Container(rules =>
rules.With(propertiesAndFields: request => request.ServiceType.Name.EndsWith("Controller") ? PropertiesAndFields.Auto(request) : null)
// .WithoutThrowOnRegisteringDisposableTransient()
// .WithTrackingDisposableTransients()
.WithoutThrowIfDependencyHasShorterReuseLifespan())
.WithDependencyInjectionAdapter(services);
Result: memory is growing up fast because of these two kind of objects stored in the scope.
If I comment .WithoutThrowOnRegisteringDisposableTransient(), my code is still working (I thought an exception would be thrown)
I tried also to declare these services as Scoped (for each http request) but it does not work because I don't create scope for each query. (Exception thrown and a scope is automatically opened per each web request by Asp .Net Core framework).
Maybe I need to dispose scope at the end of each request?
How could I force destruction of objects?
Thanks to the author of the lib, I found solution:
https://github.com/dadhi/DryIoc/issues/261
Just want to confirm my understanding is correct. If I use Single instance mode for a service:
[ServiceBehavior(InstanceContextMode=InstanceContextMode.Single)]
and this service calls a class from another asssembly which has a static constructor, that constructor is only called the first time ther service is called? The constructor I am talking about sets up a fair number of AutoMapper maps, and I only want this overhead the first time the service is called.
Taking this further, If I have two different services, and they both us the shared class, am I correct that the static constructor is still only called once?
Best
Ray
There is no connection between InstanceContextMode and how many times static constructor is fired. Static constructor is called once per Application Domain. So if your services are hosted within one Application Domain then your constructor will be called once.
As far as I understand you use the contructor to register AutoMapper configuration... To me it is not a good approach. Assuming your services are hosted on IIS you would better create a Global.asax file and then run you mapping registration code in Application_Start method. Of cource you can wrap it in some static method first.
Hope it helps!
I've been scouring the web/SO for hours now so exuse me if I missed it...
I am looking for a concrete example of how to hook into the WCF pipeline when running as a WAS hosted in IIS so that a new LINQ to SQL DataContext is automatically created and disposed when the WCF request begins and ends.
Also, when the DataContext is being disposed would it be possible/ok to call SubmitChanges() at that point to commit any changes that have been made over the course of the request?
My main goals here are to:
Have the DataContext lifecycle be tied to the request
Hide the DataContext from my domain layer so that it is easily testable.
One way to go about it would be to extend the OperationContext instance which gets created for each operation invoked in WCF. You can add extension to OperationContext. This extension can contain the DataContext instance which can be accessed and used at different location. Look at this post
Here is the scenario. I have a WCF service, when this service is called it passes control to an instance of another class (created via Ninject). In that class I need to do some work, specifically with Entity Framework and repositories. To cut a long story short, I have the following binding declared.
Bind<IGenericProductRepository>()
.To<GenericProductRepository>()
.WithConstructorArgument( "context", new StagingDataContext());
When I want to use this repository I have the following.
using (var genericProductRepository = IoC.Resolve<IGenericProductRepository>())
The problem is, that I only get a new instance of genericProductRepository if it's a brand new request, if the method is called multiple times in the same request I get an error stating that the context (the EF context) is already disposed, this is because it seems like I am getting the same instance back that was already disposed in the using statement. To explain it another way, using the Microsoft WCF Test Client, if I invoke it the first time, the code runs fine, if I push the invoke button again (without restarting the test client, i.e. the same request) then it throws this error about it being disposed already.
I have tried to play around with the various "scopes" that come with Ninject, but clearly I am missing something.
So my basic question is, how do I get a new repository whenever it hits that line, instead of using the same one ? Help would be greatly appreciated, I'm really trying to push for my company to adopt Ninject and drop Spring.
Look at your binding again. Even without any knowledge about Ninject you should notice that the instance of your context is created exactly once at the time the binding is defined. But what you want is have a new context on every resolve. Best it is done by not using WithConstructorArgument and let Ninject create the instance. Therefore you have to define a additional binding for the type of context. If this is not possible for some reason you have to use the lazy version of WithConstructorArgument
WithConstructorArgument("context", ctx => new StagingDataContext())
Furthermore, you might want to try The WCF extension for Ninject:
https://github.com/ninject/ninject.extensions.wcf
That way you can get rid of the ServiceLocator like usage.
Does anyone have any tips or best practices regarding how Autofac can help manage the NHibernate ISession Instance (in the case of an ASP.NET MVC application)?
I'm not overly familiar with how NHibernate sessions should be handled. That said, Autofac have excellent instance lifetime handling (scoping and deterministic disposal). Some related resources are this article and this question. Since you're in ASP.Net MVC land make sure you also look into the MVC integration stuff.
To illustrate the point, here's a quick sample on how you can use Autofac factory delegates and the Owned generic to get full control over instance lifetime:
public class SomeController
{
private readonly Func<Owned<ISession>> _sessionFactory;
public SomeController(Func<Owned<ISession>> sessionFactory)
{
_sessionFactory = sessionFactory;
}
public void DoSomeWork()
{
using (var session = _sessionFactory())
{
var transaction = session.Value.BeginTransaction();
....
}
}
}
The container setup to get this to work is quite simple. Notice that we don't have to do anything to get the Func<> and Owned<> types, these are made available automatically by Autofac:
builder.Register(c => cfg.BuildSessionFactory())
.As<ISessionFactory>()
.SingleInstance();
builder.Register(c => c.Resolve<ISessionFactory>().OpenSession());
Update: my reasoning here is that, according to this NHibernate tutorial, the lifetime of the session instance should be that of the "unit of work". Thus we need some way of controlling both when the session instance is created and when the session is disposed.
With Autofac we get this control by requesting a Func<> instead of the type directly. Not using Func<> would require that the session instance be created upfront before the controller instance is created.
Next, the default in Autofac is that instances have the lifetime of their container. Since we know that we need the power to dispose this instance as soon as the unit of work is done, we request an Owned instance. Disposing the owned instance will in this case immediately dispose the underlying session.
Edit: Sounds like Autofac and probably other containers can scope the lifetime correctly. If that's the case, go for it.
It isn't a good idea to use your IoC container to manage sessions directly. The lifetime of your session should correspond to your unit of work (transaction boundary). In the case of a web application, that should almost certainly be the lifetime of a web request.
The most common way to achieve this is with an HttpModule that both creates your session and starts your transaction when a request begins, then commits when the request has finished. I would have the HttpModule register the session in the HttpContext.Items collection.
In your IoC container, you could register something like HttpContextSessionLocator against ISessionLocator.
I should mention that your generic error handling should locate the current session and roll back the transaction automatically, or you could end up committing half a unit of work.