Re-instantiate a singleton with Prism in Xamarin Forms - xamarin.forms

How can I dispose and re-instantiate a singleton with Prism/DryIoC in Xamarin Forms?
I'm working with Azure Mobile Apps for offline data. Occasionally, I need to delete the local sqlite database and re-initialize it. Unfortunately the MobileServiceClient occasionally holds the db connection open and there's no method exposed to close it. The suggested solution (https://github.com/Azure/azure-mobile-apps-net-client/issues/379) is to dispose of MobileServiceClient. Only problem is that is registered with DryIoC as a singleton.
I'm not overly familiar with DryIoC, or Prism and Forms for that matter... But for the life of me, I can't see a way to do this.
I did cook up a pretty elaborate scheme that almost worked.
In my ViewModel method, when I needed the db freed up, I fired off an event -
_eventAggregator.GetEvent<RegisterDatabaseEvent>().Publish(false);
Then in App.xaml.cs, I wired up a listener and a handler like so -
_eventAggregator.GetEvent<RegisterDatabaseEvent>().Subscribe(OnRegisterDatabaseEventPublished);
private void OnRegisterDatabaseEventPublished()
{
Container.GetContainer().Unregister<IAppMobileClient>();
Container.GetContainer().Unregister<IMobileServiceClient>();
Container.GetContainer().Register<IMobileServiceClient, AppMobileClient>(new SingletonReuse());
Container.GetContainer().Register<IAppMobileClient, AppMobileClient>(new SingletonReuse());
_eventAggregator.GetEvent<RegisterDatabaseCompletedEvent>().Publish(register);
}
Lastly, back in the ViewModel constructor, I had a final listener that handled the event coming back from App.xaml and finished processing.
_eventAggregator.GetEvent<RegisterDatabaseCompletedEvent>().Subscribe(OnRegisterDatabaseCompletedEventPublished);
So the amazing thing is that this worked. The database was able to be deleted and all was good. But then I navigated to a different page and BOOM. DryIoC said it couldn't wire up the ViewModel for that page. I assume the unregister/register jacked up DryIoC for all injection... So how can I accomplish what needs to be done?
FINAL SOLUTION
Thanks so much to dadhi for taking the time to help. You are certainly a class act and I'm now considering using DryIoC elsewhere.
For anyone who stumbles on this, I'm posting the final solution below. I'll be as verbose as I can to avoid any confusion.
First, in my App.xaml.cs, I added a method for registering my database.
public void RegisterDatabase(IContainer container)
{
container.RegisterMany<AppMobileClient>(Reuse.Singleton,
setup: Setup.With(asResolutionCall: true),
ifAlreadyRegistered: IfAlreadyRegistered.Replace,
serviceTypeCondition: type =>
type == typeof(IMobileServiceClient) || type == typeof(IAppMobileClient));
}
I simply add a call to that method in RegisterTypes in place of registering the types in there directly.
protected override void RegisterTypes(IContainerRegistry containerRegistry)
{
containerRegistry.GetContainer().Rules.WithoutEagerCachingSingletonForFasterAccess();
...
RegisterDatabase(containerRegistry.GetContainer());
...
}
Note also the added rule for eager caching, per dadhi.
Later on when I need to release the database in the ViewModel... I kick things off by resetting my local db variable and sending an event to App.xaml.cs
_client = null;
_eventAggregator.GetEvent<RegisterDatabaseEvent>().Publish(true);
In App.xaml.cs, I have subscribed to that event and tied it to the following method.
private void OnRegisterDatabaseEventPublished()
{
RegisterDatabase(Container.GetContainer());
_eventAggregator.GetEvent<RegisterDatabaseCompletedEvent>().Publish(register);
}
Here I just call RegisterMany again, exactly the same as I do when the app starts up. No need to unregister anything. With the setup and ifAlreadyRegistered arguments (thanks, dadhi!), DryIoC allows the object to be replaced. Then I raise an event back to the VM letting it know the database has been released.
Finally, back in the ViewModel, I'm listening for the completed event. The handler for that event updates the local copy of the object like so.
_client = ((PrismApplication)App.Current).Container.Resolve<IAppMobileClient>();
And then I can work with the new object, as needed. This is key. Without setting _client to null above and resolving it again here, I actually ended up with 2 copies of the object and calls to methods were being hit 2x.
Hope that helps someone else looking to release their Azure Mobile Apps database!

I am not sure how exactly XF handles these things.
But in DryIoc in order for service to be fully deleted or replaced it need to be registered with setup: Setup.With(asResolutionCall: true). Read here for more details: https://bitbucket.org/dadhi/dryioc/wiki/UnregisterAndResolutionCache#markdown-header-unregister-and-resolution-cache
Update
Here are two options and considerations that work in pure DryIoc and may not work XF. But it probably may help with solution.
public class Foo
{
public IBar Bar { get; private set; }
public Foo(IBar bar) { Bar = bar; }
}
public interface IBar {}
public class Bar : IBar {}
public class Bar2 : IBar { }
[Test]
public void Replace_singleton_dependency_with_asResolutionCall()
{
var c = new Container(rules => rules.WithoutEagerCachingSingletonForFasterAccess());
c.Register<Foo>();
//c.Register<Foo>(Reuse.Singleton); // !!! If the consumer of replaced dependency is singleton, it won't work
// cause the consumer singleton should be replaced too
c.Register<IBar, Bar>(Reuse.Singleton,
setup: Setup.With(asResolutionCall: true)); // required
var foo = c.Resolve<Foo>();
Assert.IsInstanceOf<Bar>(foo.Bar);
c.Register<IBar, Bar2>(Reuse.Singleton,
setup: Setup.With(asResolutionCall: true), // required
ifAlreadyRegistered: IfAlreadyRegistered.Replace); // required
var foo2 = c.Resolve<Foo>();
Assert.IsInstanceOf<Bar2>(foo2.Bar);
}
[Test]
public void Replace_singleton_dependency_with_UseInstance()
{
var c = new Container();
c.Register<Foo>();
//c.Register<Foo>(Reuse.Singleton); // !!! If the consumer of replaced dependency is singleton, it won't work
// cause the consumer singleton should be replaced too
c.UseInstance<IBar>(new Bar());
var foo = c.Resolve<Foo>();
Assert.IsInstanceOf<Bar>(foo.Bar);
c.UseInstance<IBar>(new Bar2());
var foo2 = c.Resolve<Foo>();
Assert.IsInstanceOf<Bar2>(foo2.Bar);
}

Related

ASP.NET Some service register after mediator

We are working on service which collect data from AWS SQS then send batch to client. We are using mediator to publish notifications. The diagram of program looks like:
The problem is in first NotificationHandler from Mediatr.
private readonly EventCollectorHostedService _collector;
public CollectIncomingEventNotificationHandler(EventCollectorHostedService collector)
{
_collector = collector;
}
Class EventCollectorHostedService is register after Mediator so is not visible during registering this NotificationHandler and additionally it use Mediator to publish notification that batch is ready to send.
The error is that cannot construct CollectIncomingEventNotificationHandler because -> Unable to resolve service for type 'Api.Services.HostedServices.EventCollectorHostedService'.
services.AddMediatR(typeof(Startup).GetTypeInfo().Assembly);
services.AddHostedService<EventCollectorHostedService>();
The ugly solution is to declare some functionality in EventCollectorHostedService as static or instead of injecting EventCollectorHostedService, inject IServiceProvider.
But these solution don't look clean for me so do you have any other better solution ?
Thanks in advance.
Maybe someone encountered with similar problem so finally i have a brilliant solution.
Background services have to be treat like separate microservices based on event driven architecture so we have to make internal message broker mechanism.
The very simple solution which cover my case is:
public class NotificationChannel : INotificationChannel
{
public event EventHandler<IncomingEventNotificataionEventArgs> IncomingEventReceived;
public void Publish<T>(T notification)
{
if(notification is IncomingEventNotification incomingEventNotification)
{
OnIncomingEventReceived(incomingEventNotification);
}
}
protected virtual void OnIncomingEventReceived(IncomingEventNotification notification)
{
if(IncomingEventReceived != null)
{
var args = new IncomingEventNotificataionEventArgs(notification);
IncomingEventReceived(this, args);
}
}
}

MVVMLight Messenger.Unregister - should I unregister and how to do it?

I've looked at 'Messenger and references' discussion, but I'm writing a new topic, because my issue is not technical, and I don't want to offtop there.
I've encountered a doubt - Have I to code cleanup()/RequestCleanup() method implementation to unregister previously registered Messenger in my viewmodel class? I'm afraid of memory leaks in the future.
I think I've found the documentation not to be enough bright for me.
Description of Messenger.Register is: '... Registering a recipient does not create a hard reference to it, so if this recipient is deleted, no memory leak is caused.'
1) Is this mean that I don't have to take care of it and implement-develop following solutions?
On the other hand, we can find in the code of GalaSoft.MvvmLight.ViewModelBase abstract class the short info about the Cleanup() method:
//
// Summary:
// Unregisters this instance from the Messenger class.
// To cleanup additional resources, override this method, clean up and then
// call base.Cleanup().
public virtual void Cleanup();
so 2) Is only invoking a Cleanup enough to unregister class-instance out of the Messenger?
3) Or maybe I have to invoke Messenger.Default.Unregister(this); in the body of a Cleanup method?
4) In the Unregister(Object) doc we read 'Unregisters a messager recipient completely' - what does the 'completely' mean?
I'm very sorry if my post seems to have out of the context quotes, I wanted to point out what I'm more interested in.
EDIT 1:
Hello Joel, thanks for reply. I've got several questions:
1) I have used your code. There's defined override void Cleanup() in CustomerMasterViewModel. Where to call it? Should I declare destructor in this case or maybe the ViewModelBase has an automatic mechanism for invoking the Cleanup()?
2) I have in my project another base class from a different toolkit, so my VMs cannot derive from both at the same time. How to organise your code to get the same effect by implementing only ICleanup interface?
public class CustomerMasterViewModel : SomeBaseClass, ICleanup
{
public CustomerMasterViewModel()
{
Messenger.Default.Register<Message>(this, this.MessageReceived);
}
#region messages
private void MessageReceived(Message obj)
{
//do something
}
#endregion
#region helper methods
public override void Cleanup()
{
//base.Cleanup();//there's no implementaction in an interface
ViewModelLocator.Cleanup();
}
#endregion
}
You have to invoke the Cleanup() method in GalaSoft.MvvmLight.ViewModelBase on each of you view models you wan't to dispose don't need any longer.
Example:
Let say your application has a tab control with different tabs. Each of your tabs displays a UserControl which has a dedicated ViewModel. The user has the ability to close a tabs which causes the underlining ViewModel to become obsolete.
Want you want to do now is to clean up the ViewModel calling the Cleanup() method in GalaSoft.MvvmLight.ViewModelBase. This will unregister ALL registered messages. The GarbageCollector will take care of you viewmodel if there are no other references.
Assuming you use the ViewModelLocator which also comes with the MVVM Light Framework you're not done yet because at least the ViewModelLocator itself has a reference to your viewmodel! Therefore the Garbage Collector can't finalize your viewmodel.
But it also has another side effect. When the user reopens the tab (Lets say the user is able to do so) the UserControl is loaded again and the ViewModelLocator will give you the same ViewModel instance. The only difference is that there are not registered messages because you cleaned them by calling the CleanUp() method.
What you need is a new instance of your ViewModel. To achieve this you have to clean up your ViewModelLocator as well!
You have to unregister them (Unregister<CustomerMasterViewModel>()) one by one or simply call Reset() which will unregister all viewmodels.
Then there should be no other reference to you viewmodel and the GarbageCollector can finally take care about it.
Here is an example to do so:
ViewModelLocator:
public class ViewModelLocator
{
public ViewModelLocator()
{
ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);
SimpleIoc.Default.Register<CustomerMasterViewModel>();
}
public CustomerMasterViewModel CustomerMasterViewModel
{
get
{
return ServiceLocator.Current.GetInstance<CustomerMasterViewModel>();
}
}
public static void Cleanup()
{
SimpleIoc.Default.Reset();
//Don't forget to register them if the user attempts to open the new.
//The viewmodel initialization is lazy by default so this comes at no costs.
SimpleIoc.Default.Register<CustomerMasterViewModel>();
}
}
ViewModel
public class CustomerMasterViewModel : ViewModelBase
{
public CustomerMasterViewModel()
{
Messenger.Default.Register<Message>(this, this.MessageReceived);
}
#region messages
private void MessageReceived(Message obj)
{
//do something
}
#endregion
#region helper methods
public override void Cleanup()
{
base.Cleanup();
ViewModelLocator.Cleanup();
}
#endregion
}
In Short:
1) As far as i understood clean up is necessary after you're done.
2) Yes, calling the Cleanup() method in GalaSoft.MvvmLight.ViewModelBase will unregister all messages for this viewmodel.
3) No, see above.
4) Completely means it will unregister ALL registered messages.

ASP.net how to long polling with PokeIn?

I want to make a service that notify the user in case there are some new messages sent to him. Thus I want to use some Comet framework that provide the server push ability. So I have looked into PokeIn.
Just wondering a thing. I have checked on the samples that they have on the website. None of them look into the database to retrieve new entries if there are some. But it is just a matter of modification to it I guess.
One of the sample implement this long polling by using a sleep on the server side. So if I use the same approach I can check the database, if there are any new entries, every 5 seconds. However this approach doesn't seem to be much different from when using polling on the client side with javascript.
This part is from a sample. As can be seen they put a sleep there for to update current time for everybody.
static void UpdateClients()
{
while (true)
{
//.. code to check database
if (CometWorker.ActiveClientCount > 0)
{
CometWorker.SendToAll(JSON.Method("UpdateTime", DateTime.Now));
}
Thread.Sleep(500);
}
}
So I wonder is this how I should implement the message notifier? It seems that the above approach is still going to push a huge load demand on the server side. The message notifier is intend to work same way as the one found Facebook.
You shouldn't implement this way, that sample is only implemented like that because the keep PokeIn related part is clear. You should implement SQL part as mentioned http://www.codeproject.com/Articles/12335/Using-SqlDependency-for-data-change-events
in order to track changes on database.
So, when you have something to send, call one of the PokeIn methods for the client side delivery. I don't know, how much your application is time critical because in addition to reverse ajax, PokeIn's internal websocket feature is very easy to activate and delivers messages to client quite fast.
You can do this with database as #Zuuum said, but I implemented it in a different way.
I'm using ASP.NET MVC with PokeIn and EF in a Windows Azure environment:
I have domain events similar to this approach: Strengthening your domain: Domain Events
When someone invokes an action, that's a Unit of Work
If that UOW succeeds then I raise a domain event (e.g. ChatMessageSent)
I have subscribers for these domain events so they can receive the event and forward the message to the PokeIn listeners
I use this pattern for all my real-time needs on my game site (making moves, actions etc in a game), I don't want to advertise it here, you can find it through me if you want.
I always use this pattern as a duplex communication solution so everybody gets their update via PokeIn, even the user who invoked the action so every client will behave the same. So when someone calls an action it won't return anything except the success signal.
The next examples are won't work because they are only snippets to demonstrate the flow
Here is an action snippet from my code:
[HttpPost]
[UnitOfWork]
[RestrictToAjax]
[ValidateAntiForgeryToken]
public JsonResult Post(SendMessageViewModel msg)
{
if (ModelState.IsValid)
{
var chatMessage = new ChatMessage
{
ContainerType = msg.ContainerType,
ContainerID = msg.ContainerID,
Message = _xssEncoder.Encode(msg.Message),
User = _profileService.CurrentUser
};
_chatRepository.AddMessage(chatMessage);
OnSuccessfulUoW = () => EventBroker.Current.Send(this, new ChatMessageSentPayload(chatMessage));
}
return Json(Constants.AjaxOk);
}
And the (simplified) EventBroker implementation:
public class UnityEventBroker : EventBroker
{
private readonly IUnityContainer _container;
public UnityEventBroker(IUnityContainer container)
{
_container = container;
}
public override void Send<TPayload>(object sender, TPayload payload)
{
var subscribers = _container.ResolveAll<IEventSubscriber<TPayload>>();
if (subscribers == null) return;
foreach (var subscriber in subscribers)
{
subscriber.Receive(sender, payload);
}
}
}
And the even more simplified subscriber:
public class ChatMessageSentSubscriber : IEventSubscriber<ChatMessageSentPayload>
{
public void Receive(object sender, ChatMessageSentPayload payload)
{
var message = payload.Message;
var content = SiteContent.Global;
var clients = Client.GetClients(c => c.ContentID == message.ContainerID && c.Content == content)
.Select(c => c.ClientID)
.ToArray();
var dto = ObjectMapper.Current.Map<ChatMessage, ChatMessageSentDto>(message);
var json = PokeIn.JSON.Method("pokein", dto);
CometWorker.SendToClients(clients, json);
}
}

How and where to store nhibernate session in winforms per request

Background
I've read all kinds of blogs and documentation about nhibernate session management. My issue, is I need it for both winforms and webforms. That's right, I'm using the same data layer in both a winforms (windows .exe) and webforms (asp.net web) application. I've read a little about the unit of work pattern and is a good choice for winforms. Storing the nhibernate session in HttpRequest.Current.Items seems like a good way to go for web apps. But what about a combo deal? I have web apps, windows apps, and WCF services that all need to use the same nhibernate data layer. So back to my question...
I plan on using this design: NhibernateBestPractices in my web app like so:
private ISession ThreadSession {
get {
if (IsInWebContext()) {
return (ISession)HttpContext.Current.Items[SESSION_KEY];
}
else {
return (ISession)CallContext.GetData(SESSION_KEY);
}
}
set {
if (IsInWebContext()) {
HttpContext.Current.Items[SESSION_KEY] = value;
}
else {
CallContext.SetData(SESSION_KEY, value); // PROBLEM LINE HERE!!!
}
}
}
The Problem
The problem I am having when using this code in my windows app, is with the line
CallContext.SetData(SESSION_KEY, value);
If I understand CallContext() right, this will keep the session open the entire lifetime of my windows app because it stores the nhibernate session as part of the main applications thread. And I've heard all kinds of bad things about keeping an nhibernate session open for too long and I know by design, it's not mean to stay open very long. If all my assumptions are correct, then the above line of code is a no,no.
Given all this, I'd like to replace the above line with something that will destroy the nhibernate session more frequently in a windows app. Something similar to the lifetime of the HttpRequest. I don't want to leave it up to the windows client to know about the nhibernate session (or transaction) and when to open and close it. I'd like this to be triggered automagically.
The Question
So, where can I store the nhibernate session in a windows app that will allow me (ie. something besides the client) to automatically begin and end a transaction on a per database request (that is, whenever a client makes a call to the DB)?
** Update **
Here are 2 more links on how to implement the unit of work pattern
http://msdn.microsoft.com/en-us/magazine/dd882510.aspx
http://www.codeinsanity.com/2008/09/unit-of-work-pattern.html
Each of your apps can provide a common implementation of an interface like IUnitOfWorkStorage
public interface IUnitOfWorkStorage
{
void StoreUnitOfWork(IUnitOfWork uow);
}
IUnitOfWork can be a wrapper around the ISession which can look like this
public interface IUnitOfWork
{
void Begin();
void End();
}
Begin might open the session and start a transaction, while End would commit the transaction and close the session. So you can have 2 implementations of IUnitOfWorkStorage, one for the WebApp and one for the Windows App. The web app can use HttpContext.Current or something and your windows app can provide just a simple object store that is disposed at the end of your action which would End the UnitOfWork.
I ended up using the following code. The only "burden" it put on my app was the unit tests, and I'd rather muck up that code with session specific info that the production code. I kept the same code as mentioned in my question and then added this class to my unit test project:
namespace MyUnitTests
{
/// <summary>
/// Simulates the IHttpModule class but for windows apps.
/// There's no need to call BeginSession() and EndSession()
/// if you wrap the object in a "using" statement.
/// </summary>
public class NhibernateSessionModule : IDisposable
{
public NhibernateSessionModule()
{
NHibernateSessionManager.Instance.BeginTransaction();
}
public void BeginSession()
{
NHibernateSessionManager.Instance.BeginTransaction();
}
public void EndSession()
{
NHibernateSessionManager.Instance.CommitTransaction();
NHibernateSessionManager.Instance.CloseSession();
}
public void RollBackSession()
{
NHibernateSessionManager.Instance.RollbackTransaction();
}
#region Implementation of IDisposable
public void Dispose()
{
// if an Exception was NOT thrown then commit the transaction
if (Marshal.GetExceptionCode() == 0)
{
NHibernateSessionManager.Instance.CommitTransaction();
}
else
{
NHibernateSessionManager.Instance.RollbackTransaction();
}
CloseSession();
}
#endregion
}
}
And to use the above class you'd do something like this:
[Test]
public void GetByIdTest()
{
// begins an nhibernate session and transaction
using (new NhibernateSessionModule())
{
IMyCustomer myCust = MyCustomerDao.GetById(123);
Assert.IsNotNull(myCust);
} // ends the nhibernate transaction AND the session
}
Note: If you're using this method make to sure to not wrap your sessions in "using" statements when executing queries from your Dao classes like in this post. Because you're managing sessions yourself and keeping them open a littler longer that a single session per query, then you need to get rid of all the places you are closing the session and let the NhibernateSessionModule do that for you (web apps or windows apps).

How to pass unit of work container into constructor of repository using dependency injection

I'm trying to work out how to complete my implementation of the Repository pattern in an ASP.NET web application.
At the moment, I have a repository interface per domain class defining methods for e.g. loading and saving instances of that class.
Each repository interface is implemented by a class which does the NHibernate stuff. Castle Windsor sorts out the DI of the class into the interface according to web.config. An example of an implemented class is provided below:
public class StoredWillRepository : IStoredWillRepository
{
public StoredWill Load(int id)
{
StoredWill storedWill;
using (ISession session = NHibernateSessionFactory.OpenSession())
{
storedWill = session.Load<StoredWill>(id);
NHibernateUtil.Initialize(storedWill);
}
return storedWill;
}
public void Save(StoredWill storedWill)
{
using (ISession session = NHibernateSessionFactory.OpenSession())
{
using (ITransaction transaction = session.BeginTransaction())
{
session.SaveOrUpdate(storedWill);
transaction.Commit();
}
}
}
}
As pointed out in a previous thread, the repository class needs to accept an unit of work container (i.e. ISession) rather than instantiating it in every method.
I anticipate that the unit of work container will be created by each aspx page when needed (for example, in a property).
How do I then specify that this unit of work container instance is to be passed into the constructor of StoredWillRepository when Windsor is creating it for me?
Or is this pattern completely wrong?
Thanks again for your advice.
David
I have a persistence framework built on top of NHibernate that is used in a few Web apps. It hides the NH implementation behind an IRepository and IRepository<T> interface, with the concrete instances provided by Unity (thus I could in theory swap out NHibernate for, say, Entity Framework fairly easily).
Since Unity doesn't (or at least the version I'm using doesn't) support the passing in of constructor parameters other than those that are dependency injections themselves, passing in an extant NH ISession isn't possible; but I do want all objects in the UOW to share the same ISession.
I solve this by having a controlling repository class that manages access to the ISession on a per-thread basis:
public static ISession Session
{
get
{
lock (_lockObject)
{
// if a cached session exists, we'll use it
if (PersistenceFrameworkContext.Current.Items.ContainsKey(SESSION_KEY))
{
return (ISession)PersistenceFrameworkContext.Current.Items[NHibernateRepository.SESSION_KEY];
}
else
{
// must create a new session - note we're not caching the new session here... that's the job of
// BeginUnitOfWork().
return _factory.OpenSession(new NHibernateInterceptor());
}
}
}
}
In this example, PersistenceFrameworkContext.Current.Items accesses an IList<object> that is stored either ThreadStatic if not in a Web context, or within HttpContext.Current.Items if it is in a Web context (to avoid thread-pool problems). The first call to the property instantiates the ISession from the stored factory instance, subsequent calls just retrieve it from storage. The locking will slow things down slightly but not as much as just locking an appdomain-scoped static ISession instance.
I then have BeginUnitOfWork and EndUnitOfWork methods to take care of the UOW - I have specifically disallowed nested UOWs because frankly they were a pain to manage.
public void BeginUnitOfWork()
{
lock (_lockObject)
{
if (PersistenceFrameworkContext.Current.Items.ContainsKey(SESSION_KEY))
EndUnitOfWork();
ISession session = Session;
PersistenceFrameworkContext.Current.Items.Add(SESSION_KEY, session);
}
}
public void EndUnitOfWork()
{
lock (_lockObject)
{
if (PersistenceFrameworkContext.Current.Items.ContainsKey(SESSION_KEY))
{
ISession session = (ISession)PersistenceFrameworkContext.Current.Items[SESSION_KEY];
PersistenceFrameworkContext.Current.Items.Remove(SESSION_KEY);
session.Flush();
session.Dispose();
}
}
}
Finally, a pair of methods provide access to the domain-type-specific repositories:
public IRepository<T> For<T>()
where T : PersistentObject<T>
{
return Container.Resolve<IRepository<T>>();
}
public TRepository For<T, TRepository>()
where T : PersistentObject<T>
where TRepository : IRepository<T>
{
return Container.Resolve<TRepository>();
}
(Here, PersistentObject<T> is a base class providing ID and Equals support.)
Access to a given repository is thus in the pattern
NHibernateRepository.For<MyDomainType>().Save();
This is then facaded over such that you can use
MyDomainType.Repository.Save();
Where a given type has a specialised repository (ie needs more than it can get from IRepository<T>) then I create an interface deriving from IRepository<T>, an extending implementation inheriting from my IRepository<T> implementation, and in the domain type itself I override the static Repository property using new
new public static IUserRepository Repository
{
get
{
return MyApplication.Repository.For<User, IUserRepository>();
}
}
(MyApplication [which is called something less noddy in the real product] is a facade class which takes care of supplying the Repository instance via Unity so you have no dependency on the specific NHibernate repository implementation within your domain classes.)
This gives me full pluggability via Unity for the repository implementation, easy access to the repository in code without jumping through hoops, and transparent, per-thread ISession management.
There's lots more code than just what's above (and I've simplified the example code a great deal), but you get the general idea.
MyApplication.Repository.BeginUnitOfWork();
User user = User.Repository.FindByEmail("wibble#wobble.com");
user.FirstName = "Joe"; // change something
user.LastName = "Bloggs";
// you *can* call User.Repository.Save(user), but you don't need to, because...
MyApplication.Repository.EndUnitOfWork();
// ...causes session flush which saves the changes automatically
In my Web app, I have session-per-request, so BeginUnitOfWork and EndUnitOfWork get called in BeginRequest and EndRequest respectively.
I have a pretty similar structure to yours, and here's how I solve your question:
1) To specify my container on each method, I have a separate class ("SessionManager") which I then invoke via a static property. By doing so, here's an example using my Save implementation:
private static ISession NHibernateSession
{
get { return SessionManager.Instance.GetSession(); }
}
public T Save(T entity)
{
using (var transaction = NHibernateSession.BeginTransaction())
{
ValidateEntityValues(entity);
NHibernateSession.Save(entity);
transaction.Commit();
}
return entity;
}
2) My container is not created on each ASPX page. I instantiate all of my NHibernate goodness on the global.asax page.
** A few more things spring up **
3) You don't need to have a helper to instantiate the Load. You might as well use Get instead of Load. More information # Difference between Load and Get.
4) Using your current code, you would have to repeat pretty much the same code for each domain object you need (StoredWillRepository, PersonRepository, CategoryRepository, etc..?), which seems like a drag. You could very well use a generic class to operate over NHibernate, like:
public class Dao<T> : IDao<T>
{
public T SaveOrUpdate(T entity)
{
using (var transaction = NHibernateSession.BeginTransaction())
{
NHibernateSession.SaveOrUpdate(entity);
transaction.Commit();
}
return entity;
}
}
In my implementation, I could then use something like:
Service<StoredWill>.Instance.SaveOrUpdate(will);
Technically, the answer to my question is to use the overload of container.Resolve which allows you to specify the constructor argument as an anonymous type:
IUnitOfWork unitOfWork = [Code to get unit of work];
_storedWillRepository = container.Resolve<IStoredWillRepository>(new { unitOfWork = unitOfWork });
But let's face it, the answers provided by everyone else have been much more informative.

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