Conventional Options

I’ve really enjoyed working with the Microsoft Configuration libraries introduced with .Net Core approximately 5 years ago. The older XML-based API was quite a pain to work with, so the ConfigurationBuilder and associated types provided a long overdue need for the platform.

I had long since adopted a practice of creating discrete configuration classes populated and registered with a DI container over direct use of the ConfigurationManager class within components, so I was pleased to see the platform nudge developers in this direction through the introduction of the IOptions type.

A few aspects surrounded the prescribed use of the IOptions type of which I wasn't particularly fond were needing to inject IOptions rather than the actual options type, taking a dependency upon the Microsoft.Extensions.Options package from my library packages, and the cermony of binding the options to the IConfiguration instance. To address these concerns, I wrote some extension methods which took care of binding the type to my configuration by convention (i.e. binding a type with a suffix of Options to a section corresponding to the option type's prefix) and registering it with the container.

I’ve recently released a new version of these extensions supporting several of the most popular containers as an open source library. You can find the project here.

The following are the steps for using these extensions:

Step 1

Install ConventionalOptions for the target DI container:

$> nuget install ConventionalOptions.DependencyInjection

Step 2

Add Microsoft’s Options feature and register option types:

  services.AddOptions();
  services.RegisterOptionsFromAssemblies(Configuration, Assembly.GetExecutingAssembly());

Step 3

Create an Options class with the desired properties:

    public class OrderServiceOptions
    {
        public string StringProperty { get; set; }
        public int IntProperty { get; set; }
    }

Step 4

Provide a corresponding configuration section matching the prefix of the Options class (e.g. in appsettings.json):

{
  "OrderService": {
    "StringProperty": "Some value",
    "IntProperty": 42
  }
}

Step 5

Inject the options into types resolved from the container:

    public class OrderService
    {
        public OrderService(OrderServiceOptions options)
        {
            // ... use options
        }
    }

Currently ConventionalOptions works with Microsoft’s DI Container, Autofac, Lamar, Ninject, and StructureMap.

Enjoy!