Best way of injecting application configuration

Question

Well, I'm making my foray into this fantastic site with a question about the correct way to inject configuration settings into application components. So, the overview is : I have an application written in C# .Net 3.5. It consists of 3 assemblies - a Core, a Data and a Service. The data & service assemblies require settings retrieved from the app.config, which is done via a settings file, eg.

Code :

public static String RequestQueueConnectionString
{
    get { return ConnectionSettings.Default.RequestQueueConnectionString; }
}

Config :

<applicationSettings>
  <MyNamespace.Data.ConnectionSettings>
    <setting name="RequestQueueConnectionString" serializeAs="String">
    ...

Now, the assemblies are all setup using StructureMap for IoC - which to my mind should provide the answer to what I am looking for, but I just can't quite see it!

IoC :

public static void ConfigureStructureMap(IContainer container)
{
    container.Configure(x => ...
    ...

What I want to be able to do is to inject a configuration class already populated into the IoC container such that those settings are used for that assembly, NOT those specified in the settings file / app.config. So perhaps :

public static void ConfigureStructureMap(IContainer container, MyConfigClass config)
{
    container.Configure(x => x.For<DataConfig>()
                              .Singleton()
                              .Use ???
    ...

I hope I have provided enough details here - forgive a newbie if I have not and please let me know what else would be helpful in answering this!

Answer 1

So, after a lot of searching and trial and error, I was presented with @default.kramer's link, which I duely followed! With a little bit of trial and error, again (best way in my opinion), I managed to get the solution I was looking for. Now, whilst you can follow the link (and I would highly suggest doing so), I am going to post the solution to my question as I implemented it. Hopefully this might help someone with a similar problem.

So, I now have my configuration setup class like so :

public static class DispatchConfiguration
{
    public static void ConfigureStructureMap(IContainer container, IDispatchConfiguration dispatchConfig)
    {
        DispatchProcessBatchSize = dispatchConfig.DispatchProcessBatchSize;
        ServiceIsActive = dispatchConfig.ServiceIsActive;
        ...
    }

Now, before I was using a settings file to retrieve the configuration out of the app.config file. This was obviously good for ensuring I had flexibility in changing my config settings, but it left me with the problem of not being able to easily test those settings. Say 9/10 tests required the service to be active, but 1 test wanted to test "ServiceIsActive = false;", now I'm in trouble.

Now, however, I am able to inject the configuration from the test :

[Given(@"Config\.IsServiceActive returns false")]
public void GivenConfig_IsServiceActiveReturnsFalse()
{
    var settings = new DispatchSettings
    {
        ServiceIsActive = false,
        DispatchProcessBatchSize = 100,
        UpdatedBy = "Unit Test"    
    };

    DispatchConfiguration.ConfigureStructureMap(ObjectFactory.Container, settings);
}

And then in the real world I am able to get the settings from app.config :

public void Start(String[] args)
{
    var dispatchConfig = this.GetDispatchConfiguration();
    DispatchConfiguration.ConfigureStructureMap(ObjectFactory.Container, dispatchConfig);
    ...
}

private IDispatchConfiguration GetDispatchConfiguration()
{
    var config = (DispatchSettings)ConfigurationManager.GetSection("DispatchSettings");
    return config;
}

And then the actual config class looks like :

[XmlRoot(ElementName = "DispatchSettings", Namespace = "")]
public sealed class DispatchSettings : IDispatchConfiguration
{
    public Int32 DispatchProcessBatchSize { get; set; }
    public Boolean ServiceIsActive { get; set; }
    ...
}

For the sake of completeness the interface looks like so :

public interface IDispatchConfiguration
{
    Int32 DispatchProcessBatchSize { get; }
    Boolean ServiceIsActive { get; }
    ...
}

And finally, the config file looks like this :

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <configSections>
        <section name="DispatchSettings" type="MyNamespace.XmlConfigurator, MyNamespace.Core" />
    </configSections>

    <DispatchSettings type="MyNamespace.DispatchSettings, MyNamespace.Core">
        <ServiceIsActive>True</ServiceIsActive>
        <DispatchProcessBatchSize>100</DispatchProcessBatchSize>
    </DispatchSettings>

Now, anyone with a keen eye will spot "MyNamespace.XmlConfigurator". I found this on one of my Google journeys, and the code allows you to deserialize an Xml config into a class of your desire (as shown in this example). So, to ensure you have the complete code to make this technique work, below is the code for the XmlConfigurator. I cannot remember where I came across it, but a big thanks to the person who wrote it!!

public sealed class XmlConfigurator : IConfigurationSectionHandler
{
    public XmlConfigurator()
    {
    }

    public object Create(object parent, object configContext, XmlNode section)
    {
        XPathNavigator navigator = null;
        String typeName = null;
        Type sectionType = null;
        XmlSerializer xs = null;
        XmlNodeReader reader = null;

        try
        {
            Object settings = null;

            if (section == null)
            {
                return settings;
            }

            navigator = section.CreateNavigator();
            typeName = (string)navigator.Evaluate("string(@type)");
            sectionType = Type.GetType(typeName);
            xs = new XmlSerializer(sectionType);
            reader = new XmlNodeReader(section);

            settings = xs.Deserialize(reader);

            return settings;
        }
        finally
        {
            xs = null;
        }
    }
}

And there you have it! I hope this allows anyone with a similiar issue to resolve it and is clear enough to follow!