Lets assume I have a service IFoo and two components providing it; StandardFoo
and SpecialFoo.
SpecialFoo needs some external configuration which may fail (by throwing an
exception from the ctor, for example), and I want it to fall back to
StandardFoo
if something went wrong there.
public interface IFoo { ... }
public class StandardFoo : IFoo { ... }
public class SpecialFoo : IFoo
{
public SpecialFoo(string configFile) { if (!File.Exists(configFile))
throw new FileNotFoundException(configFile); }
}
container.Register(Component.For<IFoo>().ImplementedBy<StandardFoo>().Named("standardFoo").IsFallback());
container.Register(Component.For<IFoo>().ImplementedBy<SpecialFoo>().Named("specialFoo").DependsOn(Dependency.OnAppSettingsValue("fooConfigFile")));
In theory, I'd like IFoo to be resolved to SpecialFoo if it can, but get a
StandardFoo
if anything fails there. Maybe I misunderstood what IsFallback should do,
or maybe I'm missing something minor that makes it not work.
So far, I tried using a custom IHandlerSelector only returns the special
foo when all conditions are met (I simply moved all checks from SpecialFoo ctor
to a static method and call that before returning either the SpecialFoo or
StandardFoo
handler instead of waiting for an exception). It works, but I thought there
must be an easier way. Especially since the code doing the checks is a lot
more than the actual SpecialFoo implementation, which looks kinda off.
I also tried using a typed factory with a custom selector, but I ran into
some other problems that way...let alone the fact that it pretty much
looked like the handler selector; except that now I had an extra interface
implemented by the typed factory facility instead of directly getting my
foo injected.
So, are there any other things I could use instead that make my life a bit
easier, or is the handler selector way the one to go? Because, either way,
the handler selector works just fine without IsFallback; making me think
about what IsFallback should actually do, and whether it works correctly.
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