Question about export conditions

[darkcamper]

Hi @ipjohnson

Is it possible to export something so that it has effect when the activation happens inside a certain scope (or nested scope) ?

I'm looking for something like this:

exportRegBlock
    .Export<AClass>()
    .As<AnInterface>()
    .When.InNamedScope(SCOPE_NAME)
    .Lifestyle.SingletonPerNamedScope(SCOPENAME);

I have two exports for the same type that should be SingletonPerNamedScope, but with different scope names and I'm getting NamedScopeLocateException when activating. I don't know in compile time which class will receive the injection (so I can't use When.XXXX).

Any ideas? Thanks!

[ipjohnson]

Hi @darkcamper

Out of the box Grace doesn't support request time conditions. It's something I've thought about before but it's pretty complicated and not very performant.

That said you can simulate what you want to do with a little bit of code yourself. I've put together a quick unit test showing how to use keys and a factory to achieve picking two different types based on a request time value (i.e. scope name)

[ipjohnson]

The other option you have is you can skip the keys and Locate the types directly (this is faster at the expense of writing a little more code)

container.Configure(c =>
{
    c.Export<BasicService>();
    c.Export<CustomBasicService>();
    c.ExportFactory<IExportLocatorScope, IBasicService>(
                    scope => scope.ScopeName == "CustomScope" ? 
                                     scope.Locate<BasicService>() : 
                                     scope.Locate<CustomBasicService();
});

[darkcamper]

I finally went with the AsKeyed + Factory method option you portrayed in the unit test, as I think it's more versatile and suits my needs better.

I agree with you that choosing the activation strategy using runtime information could be less performant but it would make the export api far more powerful and straightforward in some cases. Maybe sometime in the future as an optional feature?

Thank you for your quick response!