Adding Mvc options separately after adding Mvc services

Question

A question very specific to Net Core. I would like to write an extension method for for the IServiceCollection, which will do the configuration in the application.

The reason for that, if that currently, some of the components such as attribute and controller are located in separate libraries. So, I would like to write an extension method, which will take care of configuration for each of these libraries. Configuration has to be independent of main application configuration.

Here is the current code (which I don't enjoy, because of the reason above):

public void ConfigureServices(IServiceCollection services)
{
    //..
    services.AddMvc(options => {
            // is needed for the library "filters". 
            options.Filters.Add(typeof(ExternalValidationActionFilterAttribute));
        })
        // is needed for the library "controllers"
        .AddApplicationPart(typeof(ExternalController).Assembly)
        .AddControllersAsServices();

    //..
    services.AddSingleton<ExternalControllerConfiguration>(new ExternalControllerConfiguration());
    services.AddSingleton<ExternalValidationAttributeConfiguration>(new ExternalValidationAttributeConfiguration());
}

The only method from the main application is the AddMvc(). The rest of the code is specific to external libraries. I would like to avoid mixing external library specific logic with main app logic. Ideally, refactored code should look like this:

public void ConfigureServices(IServiceCollection services)
{
    //..
    services.AddMvc();
    services.ConfigureExternalAttributes();
    services.ConfigureExternalControllers();
    //..
}

and

public static class ServiceCollectionExtensions
{
    public static void ConfigureExternalAttributes(this IServiceCollection services)
    {
        // TBD: check if Mvc services added
        //      if not - add new, with options
        //      if yes - add options to existing
        //          options.Filters.Add(typeof(ExternalValidationActionFilterAttribute));

        services.AddSingleton<ExternalValidationAttributeConfiguration>(new ExternalValidationAttributeConfiguration());
    }

    public static void ConfigureExternalControllers(this IServiceCollection services)
    {
        // TBD: check if Mvc services added
        //      if not - add new, with options
        //      if yes - add options to existing
        //          1. If 'part' not present already: .AddApplicationPart(typeof(ExternalController).Assembly)
        //          2. If 'AddControllersAsServices' not present already: .AddControllersAsServices();
        //             Else: skip

        services.AddSingleton<ExternalControllerConfiguration>(new ExternalControllerConfiguration());
    }
}

My last idea was to go to the git-hub, see the source-code and to come up with some solution. BUT. Are there any common ways of achieving this result? Maybe Microsoft had thought this though already, so I am trying to re-implement the wheel?

Any advises or code samples are very welcomed.

Answer 1

For the application part, you can create custom extension class in separate library using Microsoft.Extensions.DependencyInjection package as also suggested by Kirk Larkin.

1. Add "Microsoft.Extensions.DependencyInjection" package in your separate library.

Install-Package Microsoft.Extensions.DependencyInjection

2. Create a new class ExternalConfigurationExtensions.cs in your separate library and update class namespace as described below.

namespace Microsoft.Extensions.DependencyInjection
{
    public static class ExternalConfigurationExtensions
    {
        public static IMvcBuilder ConfigureExternalControllers(this IMvcBuilder builder)
        {
            if (builder == null)
                throw new ArgumentNullException(nameof(builder));

            builder.AddApplicationPart(typeof(ExternalController).Assembly);

            return builder;
        }
    }
}

3. Update your Startup.cs

services.AddMvc()
        .ConfigureExternalControllers();