Dynamically Updating Dependency Injection Service

Question

Background: Asp.Net Core website using Dependency Injection to relay needed services to various parts of the website

I have a service that is being added to the IServiceCollection in the ConfigureServices method in my Startup class as a singleton in the following manner:

//Settings
services.AddSingleton<ISettingsService, SettingsService>();
services.AddSingleton<ISettingsIO, SettingsIO>();
services.AddSingleton<ISettings>(f =>
{
    return f.GetService<ISettingsService>().GetSettings();
});

This works great and all the pages/controllers I need to have access to Example can do so without issue.

However, I now have the capability to change the data that is being pulled in the method GetSettings(). This means that I need to update the service that is added to the ServiceCollection.

How can I do this without changing the service from a singleton to transient?

Thanks for any help provided!

I don't understand why ISetting is also as singleton since ISettingsService is allready. Why not use it as transient or scoped and let the SettingsService who is singleton resolve it ? — Fabien ESCOFFIER
– Fabien ESCOFFIER, Commented Apr 28, 2016 at 21:04
@YacoubMassad - GetSiteSettings returns an ISiteSettings Object that it creates from a query to the DB. — khrave
– khrave, Commented Apr 28, 2016 at 21:11
@Fabien - Is there something else I would need to do other than simply change the ISettings to AddTransient? I tried that and saw no noticeable changes. — khrave
– khrave, Commented Apr 28, 2016 at 21:11
One way to do it (which might not be the cleanest way to do it) is to make GetSettings return a smart implementation of ISettings. Such implementation starts with an initial set of settings (the ones from the database) but that can then return a new set of settings. This implementation would provide means for you to set the new settings. — Yacoub Massad
– Yacoub Massad, Commented Apr 28, 2016 at 21:41

Yacoub Massad · Accepted Answer · 2016-04-28 22:11:23Z

1

As I said in the comment, this is not very clean. I think that a better solution would require more information about your system.

Create a mutable settings wrapper class:

public class MyMutableSettings : ISettings
{
    public ISettings Settings {get;set;}

    //Implement the ISettings interface by delegating to Settings, e.g.:
    public int GetNumberOfCats()
    {
        return Settings.GetNumberOfCats();
    }
}

And then you can use it like this:

MyMutableSettings mySettings = new MyMutableSettings();

services.AddSingleton<ISettings>(f =>
{
    mySettings.Settings = f.GetService<ISettingsService>().GetSettings();

    return mySettings;
});

Then, when you want to change the settings:

mySettings.Settings = GetMyNewSettings();

answered Apr 28, 2016 at 22:11

Yacoub Massad

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