StructureMap: conditionally use concrete type based on concrete instance property value

Question

I'm struggling to make StructureMap use one of concrete types sharing a common interface. This is further complicated by the fact that all candidate objects are descendants of an intermediate abstract class.

public interface ICustomer
{
    string Id { get; }
}

public abstract class CommonCustomer : ICustomer {
    public abstract string Id { get; }
}

// Fallback type if none matched
public class BaseCustomer : CommonCustomer
{
    public override string Id { get; } = "Base";
}

// Concrete type 1
public class AlphaCustomer : CommonCustomer
{
    public override string Id { get; } = "Alpha";
}

// Concrete type 2
public class BravoCustomer : CommonCustomer
{
    public override string Id { get; } = "Bravo";
}

What I tried so far:

Scan(x =>
{
    x.TheCallingAssembly();
    x.AddAllTypesOf<ICustomer>();
});

var key = "Alpha";

For<ICustomer>().Use("",
    context => context.GetAllInstances<ICustomer>()
        .FirstOrDefault(x => x.Id == key)).Singleton();
For<ICustomer>().UseIfNone<BaseCustomer>().Singleton();

How can I select a concrete type based on it's string property? And how do I scan through types which do not directly implement ICustomer?

Why exactly are the types not implementing ICustomer? There's no direct or indirect connection between your concrete types and that interface this way. — Alen Genzić
Sorry, see my edit. CommonCustomer implements ICustomer. — ttaaoossuuuu
How are you using this? What is the scenario where key changes? It looks like you need a factory to instantiate your ICustomer. — Torbjörn Hansson

Torbjörn Hansson Torbjörn Hansson · Accepted Answer · 2019-01-09T16:30:09

Sounds like you want to create a factory for instantiating ICustomer.

public interface ICustomerFactory
{
    ICustomer Create(string key);
}

public class CustomerFactory : ICustomerFactory
{
    private readonly IContainer _container;
    public CustomerFactory(IContainer container)
    {
        _container = container;
    }
    public ICustomer Create(string key) => _container.TryGetInstance<ICustomer>(key);
}

And during configuration of your container naming them:

var container = new Container(c =>
{
    c.For<ICustomerFactory>().Use<CustomerFactory>();
    c.Scan(x =>
    {
        x.TheCallingAssembly();
        x.AddAllTypesOf(typeof(ICustomer))
            .NameBy(t => ((ICustomer)Activator.CreateInstance(t, new object[0], new object[0])).Id);
    });
});

Usage:

ICustomerFactory factory;
var customer1 = factory.Create("Alpha");
var customer2 = factory.Create("Bravo");
var customer3 = factory.Create("Base");
var customer4 = factory.Create("NotExisting"); // returns null.

StructureMap: conditionally use concrete type based on concrete instance property value

1 Answers