Question

I am using Castle Windsor 2.5.1 in an ASP.NET MVC project and using property injection to create an object which I expect to always be available on a base controller class. I am using a factory to create this object, however if there is an error in the constructor, I do not get a warning from Windsor at all and it just returns my object but without injecting the property.

Is this the expected behaviour, and if so, how can I get an error raised when a factory fails to return anything?

Here is an example

public class MyDependency : IMyDependency
{
    public MyDependency(bool error)
    {
        if (error) throw new Exception("I error on creation");
    }
}

public interface IMyDependency
{
}

public class MyConsumer
{
    public IMyDependency MyDependency { get; set; }
}

[TestFixture]
public class ProgramTest
{
    [Test]
    public void CreateWithoutError() //Works as expected
    {
        var container = new WindsorContainer().Register(
            Component.For<IMyDependency>().UsingFactoryMethod(() => new MyDependency(false)).LifeStyle.Transient,
            Component.For<MyConsumer>().LifeStyle.Transient
        );

        var consumer = container.Resolve<MyConsumer>();

        Assert.IsNotNull(consumer);
        Assert.IsNotNull(consumer.MyDependency);
    }

    [Test]
    public void CreateWithError_WhatShouldHappen() //I would expect an error since it can't create MyDependency
    {
        var container = new WindsorContainer().Register(
            Component.For<IMyDependency>().UsingFactoryMethod(() => new MyDependency(true)).LifeStyle.Transient,
            Component.For<MyConsumer>().LifeStyle.Transient
        );

        Assert.Throws<Exception>(() => container.Resolve<MyConsumer>());
    }

    [Test]
    public void CreateWithError_WhatActuallyHappens() //Gives me back a consumer, but ignores MyDependency
    {
        var container = new WindsorContainer().Register(
            Component.For<IMyDependency>().UsingFactoryMethod(() => new MyDependency(true)).LifeStyle.Transient,
            Component.For<MyConsumer>().LifeStyle.Transient
        );

        var consumer = container.Resolve<MyConsumer>();

        Assert.IsNotNull(consumer);
        Assert.IsNull(consumer.MyDependency); //Basically fails silently!
    }
}

An interesting observation, if I use this in my MVC application, I get an internal error from Windsor when calling ReleaseComponent — so even though it did not give me back a class with my dependency injected, it still appears to try releasing it.

Answer 1

As far as I know, yes, that’s the intended behavior. This isn’t specific to factory methods, it works like that for all optional service dependencies.
Optional dependencies that throw when resolving are treated as non-resolvable.
This is defined in DefaultComponentActivator.ObtainPropertyValue()

Of course, you could always override the default activator with your own if you want to change this behavior.