How to read appSettings JSON from Class Library in ASP.NET Core without modifying the Class Library

Back story

I recently ran into an issue where I needed to read the settings from ASP.NET Core app into a Class Library project. Since I was creating the ASP.NET Core, I had the access to the source code. But the class library was already written and I had no access to source code and hence any change that I was suppose to do had to be done in the ASP.NET Core app.

I looked for solution and found one here : https://corderoski.wordpress.com/2017/09/18/how-to-read-appsettings-json-from-class-library-in-asp-net-core/

The solution was great as long as you have the ability to change both the ASP.NET Core app and the Class Library. Since I did not have the access to source code for the Class Library, I could not use that solution.

So I came up with following solution.

Solution

On the constructor of the ASP.NET Core app, I added the following code:

        public MyController(IConfiguration configuration)
        {
            this.configuration = configuration;
            var configFile = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
            var settings = configFile.AppSettings.Settings;
            configFile.Save(ConfigurationSaveMode.Modified);
            ConfigurationManager.RefreshSection(configFile.AppSettings.SectionInformation.Name);

            // Remove previous settings to ensure new settings are applied.
            if(settings[Settings1Key] != null)
            {
                settings.Remove(Settings1Key);
            }
            if (settings[Settings2Key] != null)
            {
                settings.Remove(Settings2Key);
            }
            if (settings[Settings3Key] != null)
            {
                settings.Remove(Settings3Key);
            }

            settings.Add("Settings1Key", this.configuration["Settings1Key"]);
            settings.Add("Settings2Key", this.configuration["Settings2Key"]);
            settings.Add("Settings3Key", this.configuration["Settings3Key"]);
            configFile.Save(ConfigurationSaveMode.Modified);
            ConfigurationManager.RefreshSection(configFile.AppSettings.SectionInformation.Name);
        }

Here the code change that I made to the Startup.cs file in the ASP.NET Core app:

        public void ConfigureServices(IServiceCollection services)
        {
            services.Configure(options =>
            {
                // This lambda determines whether user consent for non-essential cookies is needed for a given request.
                options.CheckConsentNeeded = context => true;
                options.MinimumSameSitePolicy = SameSiteMode.None;
            });

            services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
            services.AddSingleton(Configuration);
        }

That is it. What we have done here is that we pulled the settings from the appsettings.json file on run time and modified the ConfigurationManager on runtime and saved it. Now when the Class Library is called, it had the access to the configuration that it was looking for.

Happy coding!