Session null in ASP.Net MVC Controller Constructors
asp.net MvcSessionasp.net Mvc Problem Overview
Why is Session null in the constructors of Controllers? It can be accessed from Action methods. Presumably, because the MVC Routing framework is responsible for newing-up a Controller, it just hasn't (re-)instantiated the Session at that point.
Does anyone know if this is by design and, if so, why?
[I have managed to circumvent the problem by using a Lazy Loading Pattern.]
asp.net Mvc Solutions
Solution 1 - asp.net Mvc
Andrei is right - it is null because when running under the ASP.NET MVC framework, the HttpContext (and therefore HttpContext.Session) is not set when the controller class is contructed as you might expect, but it set ("injected") later by the ControllerBuilder class. If you want a better understanding of the lifecycle you can either pull down the ASP.NET MVC framework (the source is available), or refer to: this page
If you need to access the Session then one way would be to override the "OnActionExecuting" method and access it there, as it will be available by that time.
However, as Andrei is suggesting, if your code is reliant on the Session then it could potentially be difficult to write unit tests, so perhaps you could consider wrapping the Session in a helper class which can then be swapped out for a different, non-web version when running under unit tests, therefore de-coupling your controller from the web.
Solution 2 - asp.net Mvc
In addition to the other answers here, while Controller.Session is not populated in the constructor, you can still access the session through:
System.Web.HttpContext.Current.Session
with the standard caveat that this potentially reduces your controller's testability.
Solution 3 - asp.net Mvc
The Session is injected later in the life-cycle. Why do you need the session in the constructor anyway? If you need it for TDD you should wrap the session into a mockable object.
Solution 4 - asp.net Mvc
You can override the Initialize method to set your session.
protected override void Initialize(RequestContext requestContext)
Solution 5 - asp.net Mvc
If you are using an IoC Container, try injecting and using the HttpSessionStateBase instead of the Session object:
private static Container defaultContainer()
{
return new Container(ioc =>
{
// session manager setup
ioc.For<HttpSessionStateBase>()
.Use(ctx => new HttpSessionStateWrapper(HttpContext.Current.Session));
});
}
Solution 6 - asp.net Mvc
This answer might be useful for some people
If we override Initialize method then we have to initialize base class with request context : base.Initialize(requestContext);
protected override void Initialize(RequestContext requestContext)
{
base.Initialize(requestContext);
}