I inherited ASP.NET MVC 5 application which has its own Context object. The context object has few static properties that returns data from session or cache object.
For brevity purpose i have reduced the number properties to 2, one from Session and one from Cache.
public class MyContext
{
public static UserVM CurrentUser
{
get
{
return HttpContext.Current.Session.GetCurrentUserInfo();
}
}
public static IEnumerable<StateProvinceVM> StateProvincesLookup
{
get
{
return HttpContext.Current.Cache.GetStateProvinces();
}
}
}
Extension methods
/// Gets the current user information. MVC version
public static UserVM GetCurrentUserInfo(this HttpSessionStateBase session)
{
// get logged-in user from the database and put it in session ( user specific)
// and any further request for user info will be retuned from session
}
// Gets the current user information. Use when we are not in MVC context
public static CompanyUserDTO GetCurrentUserInfo(this HttpSessionState session)
{
return (new HttpSessionStateWrapper(session)).GetCurrentUserInfo();
}
// Gets the state provinces from cahe
public static IEnumerable<StateProvinceVM> GetStateProvinces(this Cache cache)
{
// load states from database and load in Cache. (application specific)
// any request from any user to States will be returned from Cache.
}
Well this implementation is working but makes unit testing hard and also i cannot inject Session and Cache. So i refactored it as below
public class MyContext
{
private static HttpSessionStateBase _session;
private static Cache _cache;
public TPTContext(HttpSessionStateBase session, Cache cache)
{
_session = session;
_cache = cache;
}
public static UserVM CurrentUser
{
get
{
return _session.GetCurrentUserInfo();
}
}
public static IEnumerable<StateProvinceVM> StateProvincesLookup
{
get
{
return _cache.LookupStateProvinces();
}
}
}
I am using Unity for DI. So im registering Session and Cache as
container.RegisterType<HttpSessionStateBase>(new InjectionFactory(x => new HttpSessionStateWrapper(System.Web.HttpContext.Current.Session)));
container.RegisterType<Cache>(new InjectionFactory(x => System.Web.HttpContext.Current.Cache));
I am not sure if my refactoring is the correct way to solve this issue. Because i am making _session as static variable. Will that cause any issue down the line since session is user specific? Will it cause Captive Dependency?
I think Cache would be okay.
or this is completely anti pattern?
Related
I've read and Googled everything on this, but can't seem to get it to work. I created a custom LifetimeManager for Unity in my MVC5 application based on these posts:
MVC3 Unity Framework and Per Session Lifetime Manager
This may be the issue I am experiencing
Here is my SessionLifetimeManager
public class SessionLifetimeManager : LifetimeManager
{
private string key = Guid.NewGuid().ToString();
public override object GetValue()
{
return HttpContext.Current.Session[key];
}
public override void RemoveValue()
{
HttpContext.Current.Session.Remove(key);
}
public override void SetValue(object newValue)
{
HttpContext.Current.Session[key] = newValue;
}
}
I only have a few types I'm playing with, here is the relevant registrations in UnityConfig.cs:
container.RegisterType<IEpiSession, EpiSession>(new SessionLifetimeManager(),
new InjectionConstructor(config.AppServerURI, config.PathToSysConfig));
container.RegisterType<IReportRepository, EpicorReportRepository>(new TransientLifetimeManager());
DependencyResolver.SetResolver(new UnityDependencyResolver(container));
Note that the EpicorReportRepository has a dependency on IEpiSession via constructor injection.
public class EpicorReportRepository : IReportRepository
{
private IEpiSession session;
// DI constructor
public EpicorReportRepository(IEpiSession session) {
this.session = session;
}
// ...
}
My Problem: After the first user / session connects to the application, every new user / session after that seems to still be using the EpiSession object and credentials that the first user had create/injected for him. This seems to be a common pattern used on the interwebs, so I'm wondering what I am missing.
How did you test that IEpiSession is the same in different Sessions?
Try to open you application from different browsers. If you open several tabs in the same browser then the same session is used.
I checked your code and it works for me.
There is the only one difference in SetResolver():
DependencyResolver.SetResolver(
type => container.Resolve(type),
types => container.ResolveAll(types));
The full registration code is the following:
public class MvcApplication : System.Web.HttpApplication
{
protected void Application_Start()
{
...
var container = new UnityContainer();
container.RegisterType<IEpiSession, EpiSession>(
new SessionLifetimeManager(),
new InjectionConstructor("config.AppServerURI", "config.PathToSysConfig"));
container.RegisterType<IReportRepository, EpicorReportRepository>(new TransientLifetimeManager());
DependencyResolver.SetResolver(
type => container.Resolve(type),
types => container.ResolveAll(types));
}
}
This is another strange problem I've encountered this days!!! I've created and MVC 4 app using nhibernate. and added a filter attribute named [LoggingNHibernateSessionAttribute] on my HomeController which manages session for each action. I've followed 'ASP.NET MVC4 and the Web API published by Apress'.
public class LoggingNHibernateSessionAttribute : ActionFilterAttribute
{
private readonly IActionLogHelper _actionLogHelper;
private readonly IActionExceptionHandler _actionExceptionHandler;
private readonly IActionTransactionHelper _actionTransactionHelper;
public LoggingNHibernateSessionAttribute()
: this(WebContainerManager.Get<IActionLogHelper>(),
WebContainerManager.Get<IActionExceptionHandler>(),
WebContainerManager.Get<IActionTransactionHelper>())
{
}
public LoggingNHibernateSessionAttribute(
IActionLogHelper actionLogHelper,
IActionExceptionHandler actionExceptionHandler,
IActionTransactionHelper actionTransactionHelper)
{
_actionLogHelper = actionLogHelper;
_actionExceptionHandler = actionExceptionHandler;
_actionTransactionHelper = actionTransactionHelper;
}
public override void OnActionExecuting(ActionExecutingContext actionExectingContext)
{
_actionLogHelper.LogEntry(actionExectingContext.ActionDescriptor);
_actionTransactionHelper.BeginTransaction();
}
public override void OnActionExecuted(ActionExecutedContext actionExecutedContext)
{
_actionTransactionHelper.EndTransaction(actionExecutedContext);
_actionTransactionHelper.CloseSession();
_actionExceptionHandler.HandleException(actionExecutedContext);
_actionLogHelper.LogExit(actionExecutedContext.ActionDescriptor);
}
}
ActionTransactionHelper
public class ActionTransactionHelper : IActionTransactionHelper
{
private readonly ISessionFactory _sessionFactory;
private readonly ICurrentSessionContextAdapter _currentSessionContextAdapter;
public ActionTransactionHelper(
ISessionFactory sessionFactory,
ICurrentSessionContextAdapter currentSessionContextAdapter)
{
_sessionFactory = sessionFactory;
_currentSessionContextAdapter = currentSessionContextAdapter;
}
public void BeginTransaction()
{
var session = _sessionFactory.GetCurrentSession();
if (session != null)
{
session.BeginTransaction();
}
}
public bool TransactionHandled { get; private set; }
public void EndTransaction(ActionExecutedContext filterContext)
{
var session = _sessionFactory.GetCurrentSession();
if (session == null) return;
if (!session.Transaction.IsActive) return;
if (filterContext.Exception == null)
{
session.Flush();
session.Transaction.Commit();
}
else
{
session.Transaction.Rollback();
}
TransactionHandled = true;
}
public bool SessionClosed { get; private set; }
public void CloseSession()
{
if (_currentSessionContextAdapter.HasBind(_sessionFactory))
{
var session = _sessionFactory.GetCurrentSession();
session.Close();
session.Dispose();
_currentSessionContextAdapter.Unbind(_sessionFactory);
SessionClosed = true;
}
}
}
when run the app, I can save an entity in the dataBase. but when I hit refresh button and exception thrown indication session is closed.
I don't know why this happens. (I searched and find this NHibernate throwing Session is closed but couldn't solve my problem).
in my NinjectConfigurator I added inRequestScope() to all of injections but no answer. I checked when I refresh the page session will be opened. but I donnow why it say session is closed?!
UPDATE:
when I first run the app. I can create a new member. but when I hit the refresh button, the session will be closed unexpectedly!!
first run:
everything works well
after hitting refresh button:
a new session bind to the current context.
the new session will be injected the repository (session is open)
the ActionTransactionHelper calls beginTransaction()
4- customMembership createUser (....) called
5- but when the _userRepositoy.save(user)called in the repository session is closed!!!!
note:but when still endTransaction and closeSession isn't called. but how session is closed?
if I comment closeSession() in onActionExecute(). session alway is open and everything woks well if refresh the page.
I checked a lot and tried different way I knew. it only happens when for the second time I want to do CRUD operations with my customMembership.
for other entities it works like a charm!
I have upoaded my sample code. for testing just create and empty database and change connection string. then go to localHost:*****/api/categories (user and pass doesn't required)
Download sample project:
Size: 47 MB
https://www.dropbox.com/s/o63wjng5f799fii/Hashem-MVC4ServicesBook.rar
size: 54 MB
Zip Format: https://www.dropbox.com/s/smrsbz4cbtznx1y/Hashem-MVC4ServicesBook2.zip
A very important thing here, could be the nature of the NHibernate. The NHibernate and its Session are in the ASP.NET MVC living longer, then could be expected. I mean not only inside of the
ActionExecuting (Controller Action starts)
ActionExecuted (the View or Redirect is called)
Session in fact must live also through the phase of rendering. Because, we could load some proxy in the "Action()" but its collection, could be lazily loaded only during the View rendering. So even in these phases Session must be opened (the same Session from the request begining)
ResultExecuting (the proxy could start to be loaded only here)
ResultExecuted (almost all is done, let's close the session)
Other words... keep the session opened throught the complete Request. From authorization untill the content is rendered.
NOTE: Anohter hint, just to be sure that all is ok, I am using this scenario (maybe you do as well):
Client FORM is about to send the data to server. The method is POST, the Action is Update()
Sent FORM is coming to server, Action Update() is triggerred - all the transactions stuff is in place (as described above)
Once NHibernate persists the data into DB, the Update() action ends, and is redirected to action
Detail() if all is ok or
Edit() if something goes wrong
The users Browser was redirected to action Detail or Edit. So if user does REFRESH, the Detail or Edit is refreshed. The Update() is not called at all (it is a POST method)
In fact, the step 1. was one of the Actions Detail or Edit. In this case, we would face this issue already...
You have this error since Asp.Net MVC does not create a new instance of LoggingNHibernateSessionAttribute every request. It creates a new instance when you request an action first time and then uses this instance in the future.
The behaviour is the following:
First invocation of Post -> new instance of 'LoggingNHibernateSession' is created
First invocation of Put -> another one instance of 'LoggingNHibernateSession' is created
Second invocation of Put -> instance of 'LoggingNHibernateSession' from previous step is used
First invocation of Delete -> another one instance of 'LoggingNHibernateSession' is created
[LoggingNHibernateSession]
public JsonResult Post(Dto data)
{
/* ... */
}
[LoggingNHibernateSession]
public JsonResult Put(int id, Dto data)
{
/* ... */
}
[LoggingNHibernateSession]
public JsonResult Delete(int id)
{
/* ... */
}
It can be solved using Func<IActionLogHelper> instead of IActionLogHelper in the constructor. An instance of IActionLogHelper can be initialised within OnActionExecuting method.
public class LoggingNHibernateSessionAttribute : ActionFilterAttribute
{
/* your code */
private readonly Func<IActionTransactionHelper> _getActionTransactionHelper;
private IActionTransactionHelper _actionTransactionHelper;
public LoggingNHibernateSessionAttribute()
: this(WebContainerManager.Get<IActionLogHelper>(),
WebContainerManager.Get<IActionExceptionHandler>(),
() => WebContainerManager.Get<IActionTransactionHelper>())
{
}
public LoggingNHibernateSessionAttribute(
IActionLogHelper actionLogHelper,
IActionExceptionHandler actionExceptionHandler,
Func<IActionTransactionHelper> getActionTransactionHelper)
{
_actionLogHelper = actionLogHelper;
_actionExceptionHandler = actionExceptionHandler;
_getActionTransactionHelper = getActionTransactionHelper;
_actionTransactionHelper = null;
}
public override void OnActionExecuting(ActionExecutingContext actionExectingContext)
{
_actionTransactionHelper = _getActionTransactionHelper();
_actionLogHelper.LogEntry(actionExectingContext.ActionDescriptor);
_actionTransactionHelper.BeginTransaction();
}
/* your code */
}
I twist myself around a workable solution to use several databases in RavenDB for an ASP.Net MVC app using Castle Windsor for the wiring.
This is the current installer
public class RavenInstaller : IWindsorInstaller
{
public void Install(IWindsorContainer container, IConfigurationStore store)
{
container.Register(
Component.For<IDocumentStore>().Instance(CreateDocumentStore()).LifeStyle.Singleton,
Component.For<IDocumentSession>().UsingFactoryMethod(GetDocumentSesssion).LifeStyle.PerWebRequest
);
}
static IDocumentStore CreateDocumentStore()
{
var store = new DocumentStore { ConnectionStringName = "RavenDb_CS9" };
store.Initialize();
IndexCreation.CreateIndexes(typeof(Users).Assembly, store);
return store;
}
static IDocumentSession GetDocumentSesssion(IKernel kernel)
{
var store = kernel.Resolve<IDocumentStore>();
return store.OpenSession();
}
}
The above works perfect but only for one Database.
I can't find the proper thinking how to handle another database. The whole chain starts with a domain service asking for an IDocumentSession. Then the flow is as specified in the above installer. But where/how do I ask for a "SessionToDb1" or a "SessionToDb2"?
The important is of course what connection string to use (where the DB property is specified) but also what indexes to create in respective DB / DocumentStore.
Did anyone accomplish this using Windsor? Am I thinking/attacking it wrong here?
Thanks!
Because you have:
Component.For<IDocumentSession>()
.UsingFactoryMethod(GetDocumentSesssion)
.LifeStyle.PerWebRequest
Your GetDocumentSession method is going to be called any time you inject an IDocumentSession. This is good.
When working with multiple databases, you need to pass the database name as a parameter to OpenSession. So, you need some way to resolve which database you would like to connect to based on the current web request.
You need to modify the GetDocumentSession method to implement whatever custom logic you are going to use. For example, you may want to look at a cookie, asp.net session item, current thread principal, or some other criteria. The decision is custom to your application, all that matters is somehow you open the session with the correct database name.
I've run into this problem before with nhibernate.
I found the best solution is to create a SessionManager class which wraps the Creation of the document store and the Session..
So I.E.
public interface ISessionManager
{
void BuildDocumentStore();
IDocumentSession OpenSession();
}
public interface ISiteSessionManager : ISessionManager
{
}
public class SiteSessionManager : ISiteSessionManager
{
IDocumentStore _documentStore;
public SiteSessionManager()
{
BuildDocumentStore();
}
public void BuildDocumentStore()
{
_documentStore = new DocumentStore
{
Url = "http://localhost:88",
DefaultDatabase = "test"
};
_documentStore.Initialize();
IndexCreation.CreateIndexes(typeof(SiteSessionManager).Assembly, _documentStore);
}
public IDocumentSession OpenSession()
{
return _documentStore.OpenSession();
}
}
// And then!.
Container.Register(Component.For<ISiteSessionManager>().Instance(new SiteSessionManager()).LifestyleSingleton());
// And then!.
public class FindUsers
{
readonly ISiteSessionManager _siteSessionManager;
public FindUsers(ISiteSessionManager siteSessionManager)
{
_siteSessionManager = siteSessionManager;
}
public IList<User> GetUsers()
{
using (var session = _siteSessionManager.OpenSession())
{
// do your query
return null;
}
}
}
Rinse and repeat for multiple databases.!
I'm building a multi-tenant web application where for security concerns, we need to have one instance of the database per tenant. So I have a MainDB for authentication and many ClientDB for application data.
I am using Asp.net MVC with Ninject and Fluent nHibernate. I have already setup my SessionFactory/Session/Repositories using Ninject and Fluent nHibernate in a Ninject Module at the start of the application. My sessions are PerRequestScope, as are repositories.
My problem is now I need to instanciate a SessionFactory (SingletonScope) instance for each of my tenants whenever one of them connects to the application and create a new session and necessary repositories for each webrequest. I'm puzzled as to how to do this and would need a concrete example.
Here's the situation.
Application starts : The user of TenantX enters his login info. SessionFactory of MainDB gets created and opens a session to the MainDB to authenticate the user. Then the application creates the auth cookie.
Tenant accesses the application : The Tenant Name + ConnectionString are extracted from MainDB and Ninject must construct a tenant specific SessionFactory (SingletonScope) for that tenant. The rest of the web request, all controllers requiring a repository will be inject with a Tenant specific session/repository based on that tenant's SessionFactory.
How do I setup that dynamic with Ninject? I was originally using Named instance when I had multiple databases but now that the databases are tenant specific, I'm lost...
After further research I can give you a better answer.
Whilst it's possible to pass a connection string to ISession.OpenSession a better approach is to create a custom ConnectionProvider. The simplest approach is to derive from DriverConnectionProvider and override the ConnectionString property:
public class TenantConnectionProvider : DriverConnectionProvider
{
protected override string ConnectionString
{
get
{
// load the tenant connection string
return "";
}
}
public override void Configure(IDictionary<string, string> settings)
{
ConfigureDriver(settings);
}
}
Using FluentNHibernate you set the provider like so:
var config = Fluently.Configure()
.Database(
MsSqlConfiguration.MsSql2008
.Provider<TenantConnectionProvider>()
)
The ConnectionProvider is evaluated each time you open a session allowing you to connect to tenant specific databases in your application.
An issue with the above approach is that the SessionFactory is shared. This is not really a problem if you are only using the first level cache (since this is tied to the session) but is if you decide to enable the second level cache (tied to the SessionFactory).
The recommended approach therefore is to have a SessionFactory-per-tenant (this would apply to schema-per-tenant and database-per-tenant strategies).
Another issue often overlooked is that although the second level cache is tied to the SessionFactory, in some cases the cache space itself is shared (reference). This can be resolved by setting the "regionName" property of the provider.
Below is a working implementation of SessionFactory-per-tenant based on your requirements.
The Tenant class contains the information we need to set up NHibernate for the tenant:
public class Tenant : IEquatable<Tenant>
{
public string Name { get; set; }
public string ConnectionString { get; set; }
public bool Equals(Tenant other)
{
if (other == null)
return false;
return other.Name.Equals(Name) && other.ConnectionString.Equals(ConnectionString);
}
public override bool Equals(object obj)
{
return Equals(obj as Tenant);
}
public override int GetHashCode()
{
return string.Concat(Name, ConnectionString).GetHashCode();
}
}
Since we'll be storing a Dictionary<Tenant, ISessionFactory> we implement the IEquatable interface so we can evaluate the Tenant keys.
The process of getting the current tenant is abstracted like so:
public interface ITenantAccessor
{
Tenant GetCurrentTenant();
}
public class DefaultTenantAccessor : ITenantAccessor
{
public Tenant GetCurrentTenant()
{
// your implementation here
return null;
}
}
Finally the NHibernateSessionSource which manages the sessions:
public interface ISessionSource
{
ISession CreateSession();
}
public class NHibernateSessionSource : ISessionSource
{
private Dictionary<Tenant, ISessionFactory> sessionFactories =
new Dictionary<Tenant, ISessionFactory>();
private static readonly object factorySyncRoot = new object();
private string defaultConnectionString =
#"Server=(local)\sqlexpress;Database=NHibernateMultiTenancy;integrated security=true;";
private readonly ISessionFactory defaultSessionFactory;
private readonly ITenantAccessor tenantAccessor;
public NHibernateSessionSource(ITenantAccessor tenantAccessor)
{
if (tenantAccessor == null)
throw new ArgumentNullException("tenantAccessor");
this.tenantAccessor = tenantAccessor;
lock (factorySyncRoot)
{
if (defaultSessionFactory != null) return;
var configuration = AssembleConfiguration("default", defaultConnectionString);
defaultSessionFactory = configuration.BuildSessionFactory();
}
}
private Configuration AssembleConfiguration(string name, string connectionString)
{
return Fluently.Configure()
.Database(
MsSqlConfiguration.MsSql2008.ConnectionString(connectionString)
)
.Mappings(cfg =>
{
cfg.FluentMappings.AddFromAssemblyOf<NHibernateSessionSource>();
})
.Cache(c =>
c.UseSecondLevelCache()
.ProviderClass<HashtableCacheProvider>()
.RegionPrefix(name)
)
.ExposeConfiguration(
c => c.SetProperty(NHibernate.Cfg.Environment.SessionFactoryName, name)
)
.BuildConfiguration();
}
private ISessionFactory GetSessionFactory(Tenant currentTenant)
{
ISessionFactory tenantSessionFactory;
sessionFactories.TryGetValue(currentTenant, out tenantSessionFactory);
if (tenantSessionFactory == null)
{
var configuration = AssembleConfiguration(currentTenant.Name, currentTenant.ConnectionString);
tenantSessionFactory = configuration.BuildSessionFactory();
lock (factorySyncRoot)
{
sessionFactories.Add(currentTenant, tenantSessionFactory);
}
}
return tenantSessionFactory;
}
public ISession CreateSession()
{
var tenant = tenantAccessor.GetCurrentTenant();
if (tenant == null)
{
return defaultSessionFactory.OpenSession();
}
return GetSessionFactory(tenant).OpenSession();
}
}
When we create an instance of NHibernateSessionSource we set up a default SessionFactory to our "default" database.
When CreateSession() is called we get a ISessionFactory instance. This will either be the default session factory (if the current tenant is null) or a tenant specific session factory. The task of locating the tenant specific session factory is performed by the GetSessionFactory method.
Finally we call OpenSession on the ISessionFactory instance we have obtained.
Note that when we create a session factory we set the SessionFactory name (for debugging/profiling purposes) and cache region prefix (for the reasons mentioned above).
Our IoC tool (in my case StructureMap) wires everything up:
x.For<ISessionSource>().Singleton().Use<NHibernateSessionSource>();
x.For<ISession>().HttpContextScoped().Use(ctx =>
ctx.GetInstance<ISessionSource>().CreateSession());
x.For<ITenantAccessor>().Use<DefaultTenantAccessor>();
Here NHibernateSessionSource is scoped as a singleton and ISession per request.
Hope this helps.
If all the databases are on the same machine, maybe the schema property of class mappings could be used to set the database on a pre-tenant basis.
I have implemented a service which uses a DAOFactory and a NHibernate Helper for the sessions and transactions. The following code is very much simplified:
public interface IService
{
IList<Disease> getDiseases();
}
public class Service : IService
{
private INHibernateHelper NHibernateHelper;
private IDAOFactory DAOFactory;
public Service(INHibernateHelper NHibernateHelper, IDAOFactory DAOFactory)
{
this.NHibernateHelper = NHibernateHelper;
this.DAOFactory = DAOFactory;
}
public IList<Disease> getDiseases()
{
return DAOFactory.getDiseaseDAO().FindAll();
}
}
public class NHibernateHelper : INHibernateHelper
{
private static ISessionFactory sessionFactory;
/// <summary>
/// SessionFactory is static because it is expensive to create and is therefore at application scope.
/// The property exists to provide 'instantiate on first use' behaviour.
/// </summary>
private static ISessionFactory SessionFactory
{
get
{
if (sessionFactory == null)
{
try
{
sessionFactory = new Configuration().Configure().AddAssembly("Bla").BuildSessionFactory();
}
catch (Exception e)
{
throw new Exception("NHibernate initialization failed.", e);
}
}
return sessionFactory;
}
}
public static ISession GetCurrentSession()
{
if (!CurrentSessionContext.HasBind(SessionFactory))
{
CurrentSessionContext.Bind(SessionFactory.OpenSession());
}
return SessionFactory.GetCurrentSession();
}
public static void DisposeSession()
{
var session = GetCurrentSession();
session.Close();
session.Dispose();
}
public static void BeginTransaction()
{
GetCurrentSession().BeginTransaction();
}
public static void CommitTransaction()
{
var session = GetCurrentSession();
if (session.Transaction.IsActive)
session.Transaction.Commit();
}
public static void RollbackTransaction()
{
var session = GetCurrentSession();
if (session.Transaction.IsActive)
session.Transaction.Rollback();
}
}
At the end of the day I just want to expose the IService to ASP.NET MVC/Console application/Winform. I can already use the Service in a console application but would like to improve it first. I guess the first improvement would be to inject the interfaces INHibernateHelper and IDAOFactory via castle. But I think the problem is that the NHibernateHelper might cause problems in a asp.net context where NHibernateHelper should run according to the 'Nhibernate session per request' pattern. One question I have is whether this pattern is determined by the nhibernate config section (setting current_session_context_class = web) or can i control this via castle somehow?
I hope this makes sense. The final aim is just to expose THE IService.
Thanks.
Christian
You have two choices..
1) Host it in WCF. This allows you access from any source you want.
2) Abstract away everything that's specific to how the code is being used. In our system for instance we use our own Unit Of Work implementation which is stored differently based on where the code is running. A small example would be storing something using the WCF call context vs. the current thread.