Is there a way to override ConfigurationManager.AppSettings?

Question

I really want to be able to have a way to take an app that currently gets its settings using ConfigurationManager.AppSettings["mysettingkey"] to actually have those settings come from a centralized database instead of the app.config file. I can make a custom config section for handling this sort of thing, but I really don't want other developers on my team to have to change their code to use my new DbConfiguration custom section. I just want them to be able to call AppSettings the way they always have but have it be loaded from a central database.

Any ideas?

Answer 1

If you don't mind hacking around the framework and you can reasonably assume the .net framework version the application is running on (i.e. it's a web application or an intranet application) then you could try something like this:

using System; using System.Collections.Specialized; using System.Configuration; using System.Configuration.Internal; using System.Reflection;  static class ConfigOverrideTest {   sealed class ConfigProxy:IInternalConfigSystem   {     readonly IInternalConfigSystem baseconf;      public ConfigProxy(IInternalConfigSystem baseconf)     {       this.baseconf = baseconf;     }      object appsettings;     public object GetSection(string configKey)     {       if(configKey == "appSettings" && this.appsettings != null) return this.appsettings;       object o = baseconf.GetSection(configKey);       if(configKey == "appSettings" && o is NameValueCollection)       {         // create a new collection because the underlying collection is read-only         var cfg = new NameValueCollection((NameValueCollection)o);         // add or replace your settings         cfg["test"] = "Hello world";         o = this.appsettings = cfg;       }       return o;     }      public void RefreshConfig(string sectionName)     {       if(sectionName == "appSettings") appsettings = null;       baseconf.RefreshConfig(sectionName);     }      public bool SupportsUserConfig     {       get { return baseconf.SupportsUserConfig; }     }   }    static void Main()   {     // initialize the ConfigurationManager     object o = ConfigurationManager.AppSettings;     // hack your proxy IInternalConfigSystem into the ConfigurationManager     FieldInfo s_configSystem = typeof(ConfigurationManager).GetField("s_configSystem", BindingFlags.Static | BindingFlags.NonPublic);     s_configSystem.SetValue(null, new ConfigProxy((IInternalConfigSystem)s_configSystem.GetValue(null)));     // test it     Console.WriteLine(ConfigurationManager.AppSettings["test"] == "Hello world" ? "Success!" : "Failure!");   } } 

Answer 2

Whatever you do you will need to add one layer of redirection? ConfigurationManager.AppSettings["key"] will always look in the configuration file. You can make a ConfigurationFromDatabaseManager but this will result in using different calling syntax:

ConfigurationFromDatabaseManager.AppSettings["key"] instead of ConfigurationSettings["key"].