Mvc Core Dynamically bind Configuration

Question

I am wondering if it is possible to bind a configuration section to an object dynamically. Normally to bind a configuration section we would write code like this:

var section = Configuration.GetSection(nameof(MyCustomSection));
services.Configure<MyCustomSection>(o => secto.Bind(o));

I am wondering if its possible to do it without declaring the type <MyCustomSection>.

//This doesn't work, just trying to show you how I would like to do it
services.Configure(MyType, o => section.Bind(o));

For example, if I wish to bind injection I can do it like this:

services.AddTransient<IDateTime, SystemDateTime>();

But I can also do it in a dynamic way such as this:

services.AddTransient(Type1, Type2));

Is the same possible for services.Configure? I looked at method parameters but it doesn't seem to support it. Just wondering if there is another way or maybe I'm just overlooking something?

EDIT:

services.AddSingleton(p =>   
{
    var type = new MySection();
    Configuration.GetSection("MySection").Bind(type);
    return type;
});

Then I call it in a class like this:

public class Test {
    public Test(IOptions<MySection> section)
    {
        var finalValue = section.Value;
    }
}

finalValue is always null;

Nkosi · Accepted Answer · 2018-06-25 17:47:56Z

3

First off, all Configure does is

bind the configuration section to a particular type and
register that type with the service collection, such that it may be injected directly.

Therefore, if Configure doesn't have an overload to do what you want, you can simply jump down to the individual tasks, i.e.

services.AddSingleton(p =>
{
    var config = Activator.CreateInstance(type);
    Configuration.GetSection("Foo").Bind(config);
    return config;
}

edited Jun 25, 2018 at 17:47

Nkosi

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answered Jun 25, 2018 at 17:02

Chris Pratt

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4 Comments

Bagzli Over a year ago

I tried following your example and it always gives me a null value. I have updated my question with the code I tried based on your example. Do you know if I've missed something?

Chris Pratt Over a year ago

I imagine it's some issue with how you're getting the SectionName, i.e. that is probably returning null or something, such that it's not actually find a section to bind to. FWIW, I tested this code in my own project, and can confirm it works.

Bagzli Over a year ago

The issues is that I have been trying to call IOptions<MyType> as opposed to just MyType. This solution ultimately gives me dynamic binding, but it doesn't go through IOptions anymore.

Chris Pratt Over a year ago

You don't need IOptions anyways. The only value is in IOptionsSnapshot, but I was unfortunately unable to find a way to make that work. So, you don't get reload with this method, but depending in your application that may not matter.

Neil · Accepted Answer · 2018-06-25 20:49:49Z

3

If you really wanted to, you could use reflection to call services.Configure<TOptions>() with a dynamic generic type argument at runtime. However, there may be a simpler way to get your desired result (using IOptions<>) using some modification of Chris's answer.

Use it like so:

services.Configure(MyType, o => { var castObj = (MyType)o; section.Bind(castObj); });

using System;
using System.Linq;
using Microsoft.Extensions.DependencyInjection;

namespace WebApplication1
{
    public static class MyServiceExtensions
    {
        public static IServiceCollection Configure(this IServiceCollection services, Type type, Action<object> configureOptions)
        {
            // Static type that contains the extension method
            var extMethodType = typeof(OptionsServiceCollectionExtensions);

            // Find the overload for Configure<TOptions>(IServiceCollection, Action<TOptions>)
            // This could be more specific to make sure that all type arguments are exactly correct.
            // As it stands, this returns the correct overload but future updates to OptionsServiceCollectionExtensions
            // may add additional overloads which will require this to be updated.
            var genericConfigureMethodInfo = extMethodType.GetMethods()
                .Where(m => m.IsGenericMethod && m.Name == "Configure")
                .Select(m => new
                {
                    Method = m,
                    Params = m.GetParameters(),
                    Args = m.GetGenericArguments() // Generic Type[] (ex [TOptions])
                })
                .Where(m => m.Args.Length == 1 && m.Params.Length == 2
                    && m.Params[0].ParameterType == typeof(IServiceCollection))
                .Select(m => m.Method)
                .Single();

            var method = genericConfigureMethodInfo.MakeGenericMethod(type);

            // Invoke the method via reflection with our converted Action<objct> delegate
            // Since this is an extension method, it is static and services is passed
            // as the first parameter instead of the target object
            method.Invoke(null, new object[] { services, configureOptions });

            return services;
        }
    }
}

answered Jun 25, 2018 at 20:49

Neil

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2 Comments

Bagzli Over a year ago

I think the answer is correct, however, it is such an overkill haha. I was really hoping there was a built-in way I'm missing out on.

Neil Over a year ago

You may find a cleaner way to inject the configured options via IOptions if you looked at the open source implementation of .Configure<>(), but this solution should work just fine. I didn't do any tests of this with type inheritance so there may be something overlooked there

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