New To StructureMap - Getting No Default Instance Error 202

Question

Hi. I am very new to StructureMap and am getting the following error:

StructureMap Exception Code: 202 No Default Instance defined for PluginFamily Company.ProjectCore.Core.IUserSession, Company.ProjectCore, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null

It seems to be hitting the first interface instance on compile and then throws the above error:

private readonly IUserSession _userSession;

public SiteMaster()
{
  _userSession = ObjectFactory.GetInstance<IUserSession>(); // ERROR THROWN HERE
  ...
}

For what it is worth, I have the PluginFamily reference above all of interfaces:

[PluginFamily("Default")]
public interface IUserSession

Below is my entire StructureMap.config

<StructureMap>
  <Assembly Name="Company.ProjectWeb" />
  <Assembly Name="Company.ProjectCore" />
  <!--
  Use DefaultKey="Default" for standard cache 
  or DefaultKey="MemCached" for memcached cache.
  -->
  <PluginFamily
      Assembly="Company.ProjectCore"
      Type="Company.ProjectCore.Core.ICache"
      DefaultKey="MemCached" />
  <!--
  Use DefaultKey="Default" for sending the email
  in real time through the configured mail server 
  or use DefaultKey="MailQueue" to send the mail
  in batches through another process
  -->
  <PluginFamily
      Assembly="Company.ProjectCore"
      Type="Company.ProjectCore.Core.IEmailService"
      DefaultKey="MailQueue" />
  <!--
  Use DefaultKey="Default" for standard cache 
  or DefaultKey="UserSession" for memcached cache.
  -->
  <PluginFamily
      Assembly="Company.ProjectCore"
      Type="Company.ProjectCore.Core.IUserSession"
      DefaultKey="UserSession" />
  <!--
  Use DefaultKey="Default" for standard cache 
  or DefaultKey="Redirector" for memcached cache.
  -->
  <PluginFamily
      Assembly="Company.ProjectCore"
      Type="Company.ProjectCore.Core.IRedirector"
      DefaultKey="Redirector" />
  <!--
  Use DefaultKey="Default" for standard cache 
  or DefaultKey="Navigation" for memcached cache.
  -->
  <PluginFamily
      Assembly="Company.ProjectCore"
      Type="Company.ProjectCore.Core.INavigation"
      DefaultKey="Navigation" />

Any suggestions? Thanks.

Answer 1

The config looks correct to me at first glance. Are you calling ObjectFactory.Initialize before the code you posted runs?

I don't use attributes or config files myself (anymore), but I don't think you need to use both.

Also, is there a reason you want to use attributes and/or XML in the first place? You can configure your instances via code with StructureMap via a fluent interface, and IMHO this is a better way of doing it (unless you need to swap implementations in production, but even then there are other options).

See also: http://structuremap.github.com/structuremap/ConfiguringStructureMap.htm

Update After Comments

Ok, so I downloaded the app, but can't get it to run, and can't really take the time to troubleshoot. So I'm sorry if I can't help any further.

However I did poke around the code very briefly, and I can tell you definitively that some of the code I saw for using IOC/DI is very disturbing. Unless this is starter code that the book then shows you how to refactor, I would not recommend this as a source for learning the IOC pattern or StructureMap.

Here is an example of bad code:

public AccountService()
{
    _accountRepository = ObjectFactory.GetInstance<IAccountRepository>();
    _permissionRepository = ObjectFactory.GetInstance<IPermissionRepository>();
    _userSession = ObjectFactory.GetInstance<IUserSession>();
    _redirector = ObjectFactory.GetInstance<IRedirector>();
    _email = ObjectFactory.GetInstance<IEmail>();
    _profileService = ObjectFactory.GetInstance<IProfileService>();
    _webContext = ObjectFactory.GetInstance<IWebContext>();
    _friendService = ObjectFactory.GetInstance<IFriendService>();
}

To me this a clear Global Service Locator anti-pattern. Even barring that, it is violating one of the core principles of IOC, which is that dependencies should be explicit.

Your application should have few (or even one, if possible) call to ObjectFactory.GetInstance(), and from that point on, all dependencies should be handled through the framework as constructor arguments.

So the constructor for Account Service would look something like:

public AccountService(IAccountRepository accountRepository) 
    {
        //all arguments (not just account repo) would be passed into the ctor
        //you also want to check for null for all arguments
        _accountRepository = accountRepository;
    }

(also note that 8 arguments is LIKELY a sign that this class has too many responsibilities)

It's really too much to get into in a single post, but I would recommend finding a better source for learning the pattern and tool.

Answer 2

The author of StructureMap has discouraged the use of the XML declaration. Why not declare it with code, like this:

ObjectFactory.Initialize(x => 
    {
        x.For<ICache>().Use<MemCached>();
        x.For<IEmailService>().Use<MailQueue>();
        x.For<IUserSession>().Use<UserSession>();
        x.For<IRedirector>().Use<Redirector>();
        x.For<INavigation>().Use<Navigation>();
    });

That way you won't have to guess about whether things are wired correctly. It's also much easier to maintain and less code.