constructor parameters on controller actions

Question

I am trying to create a custom manager which is passed in the controller when it is being called and I am having troubles understanding the current implementation of new MVC5 project in c#.

Here is the default implementation:

public AccountController(ApplicationUserManager userManager, ApplicationSignInManager signInManager )
{
    UserManager = userManager;
    SignInManager = signInManager;
}

above all of that are declarations for them:

public ApplicationSignInManager SignInManager
{
    get
    {
        return _signInManager ?? HttpContext.GetOwinContext().Get<ApplicationSignInManager>();
    }
    private set 
    { 
        _signInManager = value; 
    }
}

public ApplicationUserManager UserManager
{
    get
    {
        return _userManager ?? HttpContext.GetOwinContext().GetUserManager<ApplicationUserManager>();
    }
    private set
    {
        _userManager = value;
    }
}

Now from my understanding the SignInManager and UserManager get created when application gets created for the first time in Startup.Auth.cs which looks like this:

app.CreatePerOwinContext<ApplicationUserManager>(ApplicationUserManager.Create);
app.CreatePerOwinContext<ApplicationSignInManager>(ApplicationSignInManager.Create);

So now whenever I call UserManager I will get that first instance that was created when project ran for the first time.

I have 2 questions. Question 1 is is anything I said above wrong and Do I have a wrong understanding of how MVC5 works?

Question2: How is UserManager and SignInManager generated and passed in the controller? Where is the code that creates that first instance of the manager and passes it in the controller? I am assuming it is app.CreatePerOwnContext that does it. If so, can I then just create my own Manager and then register it with Owin in the same fashion and reuse throughout the project? Will my code get the latest data from the database if I do this and not cache it?

Answer 1

The code you're showing is coming from the IMO very ugly MVC5 template, which works out of the box but does some ugly things.

This constructor:

public AccountController(ApplicationUserManager userManager, 
       ApplicationSignInManager signInManager)

makes you think OWIN automagically injects the managers for you. But in fact this is not the case. That is why the template comes with the ugly properties you supplied in the questions. When you do not change anything to the template, the default constructor is called (also present in the template). To try it, just delete, or comment, the default constructor and you'll see the AccountController can't be created anymore.

So what is actually happening there is that both managers are located using the Service Locator anti pattern in the getters of the supplied properties.

So now whenever I call UserManager I will get that first instance that was created when project ran for the first time?

No this is not the case. What this line:

 app.CreatePerOwinContext<ApplicationUserManager>(ApplicationUserManager.Create);

does, is creating a delegate to the Create method of both managers. The managers are cached within an Owin Request. The next request the delegates are called again and you get a fresh ApplicationUserManager etc.

To be a little bit more verbose this line could be rewritten as:

Func<ApplicationUserManager> userManagerFactory = () => ApplicationUserMangager.Create();
app.CreatePerOwinContext<ApplicationUserManager>(userManagerFactory);

So if you would a breakpoint here:

public ApplicationUserManager UserManager
{
    get
    {
        // place breakpoint here
         return _userManager ?? HttpContext.GetOwinContext().GetUserManager<ApplicationUserManager>();
    }
// ....

You would see that while stepping through the code, you will hit the line where you created the UserManagerFactory which in his turn will call the Create() method of the ApplicationUserManager.

How is UserManager and SignInManager generated and passed in the controller

It isn't! You would need to use dependency injection for that.

If so, can I then just create my own Manager and then register it with Owin in the same fashion and reuse throughout the project

Yes you can. You can completely refactor the ApplicationUserManager you also got 'for free' in the template. As long as you supply a factory method to the 'CreatePerOwinContext' extension method.

Will my code get the latest data from the database if I do this and not cache it? The instances are cached on per request base. So each request you will get a new one, with a new DbContext etc.

I'm unsure how familiar you are with dependency injection but MVC5 is a pretty easy framework to start with it, IMO.

I once wrote a blogpost how to configure my DI container of choice (Simple Injector) to use with the MVC5 template. I also wrote several answers here on SO regarding this template: specifically this one, should interest you. This one is interesting also!