Variables within app config web config

Question

Is it is possible to do something like the following in the app config or web config files    lt appSettings gt    lt add key  MyBaseDir  value  C  MyBase    gt    lt add key  Dir1  value   MyBaseDir  Dir1   gt    lt add key  Dir2  value   MyBaseDir  Dir2   gt   lt  appSettings gt    I then want to access Dir2 in my code by simply saying    ConfigurationManager AppSettings  Dir2     This will help me when I install my application in different servers and locations wherein I will only have to change ONE entry in my entire app config   I know I can manage all the concatenation in code  but I prefer it this way

User · Answer

I thought I just saw this question   In short  no  there s no variable interpolation within an application configuration    You have two options   You could roll your own to substitute variables at runtime At build time  massage the application configuration to the particular specifics of the target deployment environment  Some details on this at dealing with the configuration-nightmare

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A slightly more complicated  but far more flexible  alternative is to create a class that represents a configuration section   In your app config   web config file  you can have this    lt  xml version  1 0  encoding  utf-8    gt   lt configuration gt       lt  -- This section must be the first section within the  lt configuration gt  node -- gt       lt configSections gt           lt section name  DirectoryInfo  type  MyProjectNamespace DirectoryInfoConfigSection  MyProjectAssemblyName    gt       lt  configSections gt        lt DirectoryInfo gt           lt Directory MyBaseDir  C  MyBase  Dir1  Dir1  Dir2  Dir2    gt       lt  DirectoryInfo gt   lt  configuration gt    Then  in your  NET code  I ll use C  in my example   you can create two classes like this   using System  using System Configuration   namespace MyProjectNamespace        public class DirectoryInfoConfigSection   ConfigurationSection             ConfigurationProperty  Directory            public DirectoryConfigElement Directory               get                   return  DirectoryConfigElement base  Directory                             public class DirectoryConfigElement   ConfigurationElement             ConfigurationProperty  MyBaseDir            public String BaseDirectory               get                   return  String base  MyBaseDir                                      ConfigurationProperty  Dir1            public String Directory1               get                   return  String base  Dir1                                      ConfigurationProperty  Dir2            public String Directory2               get                   return  String base  Dir2                                       You can make custom properties to combine your directory names          public String Directory1Resolved               get                   return System IO Path Combine BaseDirectory  Directory1                                     Finally  in your program code  you can access your app config variables  using your new classes  in this manner   DirectoryInfoConfigSection config      DirectoryInfoConfigSection ConfigurationManager GetSection  DirectoryInfo    String dir1Path   config Directory Directory1Resolved      This value will equal  C  MyBase Dir1

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For rolling out products where we need to configure a lot of items with similar values  we use small console apps that read the XML and update based on the parameters passed in   These are then called by the installer after it has asked the user for the required information

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I would recommend following Matt Hamsmith s solution  If it s an issue to implement  then why not create an extension method that implements this in the background on the AppSettings class   Something like       public static string GetValue this NameValueCollection settings  string key                 Inside the method you search through the DictionaryInfoConfigSection using Linq and return the value with the matching key  You ll need to update the config file though  to something along these lines    lt appSettings gt     lt DirectoryMappings gt       lt DirectoryMap key  MyBaseDir  value  C  MyBase    gt       lt DirectoryMap key  Dir1  value   MyBaseDir  Dir1   gt       lt DirectoryMap key  Dir2  value   MyBaseDir  Dir2   gt     lt  DirectoryMappings gt   lt  appSettings gt

User · Answer

Three Possible Solutions     I know I m coming late to the party  I ve been looking if there were any new solutions to the variable configuration settings problem  There are a few answers that touch the solutions I have used in the past but most seem a bit convoluted  I thought I d look at my old solutions and put the implementations together so that it might help people that are struggling with the same problem     For this example I have used the following app setting in a console application    lt appSettings gt       lt add key  EnvironmentVariableExample  value   BaseDir  bin   gt       lt add key  StaticClassExample  value  bin   gt       lt add key  InterpollationExample  value   0 bin   gt     lt  appSettings gt    1  Use environment variables     I believe autocro autocro s answer touched on it  I m just doing an implementation that should suffice when building or debugging without having to close visual studio  I have used this solution back in the day       Create a pre-build event that will use the MSBuild variables     Warning  Use a variable that will not be replaced easily so use your project name or something similar as a variable name    SETX BaseDir    ProjectDir   Reset variables  using something like the following   Refresh Environment Variables on Stack Overflow Use the setting in your code       private void Test Environment Variables         string BaseDir   ConfigurationManager AppSettings  EnvironmentVariableExample        string ExpandedPath   Environment ExpandEnvironmentVariables BaseDir  Replace              The function addes a   at the end of the variable     Console WriteLine   From within the C  Console Application  ExpandedPath            2  Use string interpolation    Use the string Format   function      private void Test Interpollation         string ConfigPath   ConfigurationManager AppSettings  InterpollationExample        string SolutionPath   Path GetFullPath Path Combine System AppDomain CurrentDomain BaseDirectory                   string ExpandedPath   string Format ConfigPath  SolutionPath ToString         Console WriteLine   Using old interpollation  ExpandedPath            3  Using a static class  This is the solution I mostly use    The implementation      private void Test Static Class         Console WriteLine   Using a static config class  Configuration BinPath             The static class      static class Configuration       public static string BinPath               get                       string ConfigPath   ConfigurationManager AppSettings  StaticClassExample                string SolutionPath   Path GetFullPath Path Combine System AppDomain CurrentDomain BaseDirectory                           return SolutionPath   ConfigPath                         Project Code   App config    lt  xml version  1 0  encoding  utf-8    gt   lt configuration gt       lt startup gt            lt supportedRuntime version  v4 0  sku   NETFramework Version v4 6 1    gt       lt  startup gt     lt appSettings gt       lt add key  EnvironmentVariableExample  value   BaseDir  bin   gt       lt add key  StaticClassExample  value  bin   gt       lt add key  InterpollationExample  value   0 bin   gt     lt  appSettings gt   lt  configuration gt    Program cs  using System  using System Configuration  using System IO   namespace ConfigInterpollation       class Program               static void Main string   args                        new Console Tests   Run Tests                Console WriteLine  Press enter to exit                Console ReadLine                                 internal class Console Tests               public void Run Tests                         Test Environment Variables                Test Interpollation                Test Static Class                      private void Test Environment Variables                         string ConfigPath   ConfigurationManager AppSettings  EnvironmentVariableExample                string ExpandedPath   Environment ExpandEnvironmentVariables ConfigPath  Replace                        Console WriteLine   Using environment variables  ExpandedPath                        private void Test Interpollation                         string ConfigPath   ConfigurationManager AppSettings  InterpollationExample                string SolutionPath   Path GetFullPath Path Combine System AppDomain CurrentDomain BaseDirectory                           string ExpandedPath   string Format ConfigPath  SolutionPath ToString                 Console WriteLine   Using interpollation  ExpandedPath                        private void Test Static Class                         Console WriteLine   Using a static config class  Configuration BinPath                          static class Configuration               public static string BinPath                       get                               string ConfigPath   ConfigurationManager AppSettings  StaticClassExample                    string SolutionPath   Path GetFullPath Path Combine System AppDomain CurrentDomain BaseDirectory                               return SolutionPath   ConfigPath                                    Pre-build event   Project Settings -  Build Events

User · Answer

I m struggling a bit with what you want  but you can add an override file to the app settings then have that override file set on a per environment basis    lt appSettings file     OverrideSettings config  gt

User · Answer

Usally  I end up writing a static class with properties to access each of the settings of my web config   public static class ConfigManager        public static string MyBaseDir               return ConfigurationManager AppSettings  MyBaseDir   toString               public static string Dir1               return MyBaseDir   ConfigurationManager AppSettings  Dir1   toString               Usually  I also do type conversions when required in this class  It allows to have a typed access to your config  and if settings change  you can edit them in only one place   Usually  replacing settings with this class is relatively easy and provides a much greater maintainability

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I came up with this solution    In the application Settings settings I defined a variable ConfigurationBase  with type string Scope Application  I introduced a variable in the target attributes in the Settings settings  all those attributes had to be set to Scope User In the app xaml cs I read out the value if the ConfigurationBase In the app xaml cs I replaced all variables with the ConfigurationBase value  In order to replace the values at run-time the attributes had to be set to Scopr User   I m not really happy with this solution because I have to change all attributes manually  if I add a new one I have to regard it in the app xaml cs   Here a code snippet from the App xaml cs   string configBase   Settings Default ConfigurationBase  Settings Default CommonOutput Directory   Settings Default CommonOutput Directory Replace    ConfigurationBase    configBase     UPDATE  Just found an improvement  again a code snippet from the app xaml cs    string configBase   Settings Default ConfigurationBase   foreach  SettingsProperty settingsProperty in Settings Default Properties        if   settingsProperty IsReadOnly  amp  amp  settings Default settingsProperty Name  is string                Settings Default settingsProperty Name      string Settings Default settingsProperty Name   Replace    ConfigurationBase    configBase             Now the replacements work for all attributes in my settings that have Type string and Scope User  I think I like it this way   UPDATE2  Apparently setting Scope Application is not required when running over the properties

User · Answer

You can use environment variables in your app config for that scenario you describe   lt configuration gt     lt appSettings gt       lt add key  Dir1  value   MyBaseDir  Dir1   gt     lt  appSettings gt   lt  configuration gt    Then you can easily get the path with   var pathFromConfig   ConfigurationManager AppSettings  Dir1    var expandedPath   Environment ExpandEnvironmentVariables pathFromConfig

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I don t think you can declare and use variables to define appSettings keys within a configuration file  I ve always managed concatenations in code like you

User · Answer

I would suggest you DslConfig  With DslConfig you can use hierarchical config files from Global Config  Config per server host to config per application on each server host  see the AppSpike   If this is to complicated for you you can just use the global config Variables var Just configure in Varibales var  baseDir    C  MyBase  Var  MyBaseDir     baseDir Var  Dir1     baseDir     Dir1  Var  Dir2     baseDir     Dir2    And get the config values with  Configuration config   new DslConfig BooDslConfiguration   config GetVariable lt string gt   MyBaseDir   config GetVariable lt string gt   Dir1   config GetVariable lt string gt   Dir2

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You can accomplish using my library Expansive  Also available on nuget here   It was designed with this as a primary use-case   Moderate Example  using AppSettings as default source for token expansion   In app config    lt configuration gt       lt appSettings gt           lt add key  Domain  value  mycompany com   gt           lt add key  ServerName  value  db01  Domain    gt       lt  appSettings gt       lt connectionStrings gt           lt add name  Default  connectionString  server  ServerName  uid uid pwd pwd Initial Catalog master   provider  System Data SqlClient    gt       lt  connectionStrings gt   lt  configuration gt    Use the  Expand   extension method on the string to be expanded   var connectionString   ConfigurationManager ConnectionStrings  Default   ConnectionString  connectionString Expand      returns  server db01 mycompany com uid uid pwd pwd Initial Catalog master     or  Use the Dynamic ConfigurationManager wrapper  Config  as follows  Explicit call to Expand   not necessary    var serverName   Config AppSettings ServerName     returns  db01 mycompany com   var connectionString   Config ConnectionStrings Default     returns  server db01 mycompany com uid uid pwd pwd Initial Catalog master     Advanced Example 1  using AppSettings as default source for token expansion   In app config    lt configuration gt       lt appSettings gt           lt add key  Environment  value  dev   gt           lt add key  Domain  value  mycompany com   gt           lt add key  UserId  value  uid   gt           lt add key  Password  value  pwd   gt           lt add key  ServerName  value  db01- Environment   Domain    gt           lt add key  ReportPath  value     ServerName  SomeFileShare   gt       lt  appSettings gt       lt connectionStrings gt           lt add name  Default  connectionString  server  ServerName  uid  UserId  pwd  Password  Initial Catalog master   provider  System Data SqlClient    gt       lt  connectionStrings gt   lt  configuration gt    Use the  Expand   extension method on the string to be expanded   var connectionString   ConfigurationManager ConnectionStrings  Default   ConnectionString  connectionString Expand      returns  server db01-dev mycompany com uid uid pwd pwd Initial Catalog master

User · Answer

Good question   I don t think there is  I believe it would have been quite well known if there was an easy way  and I see that Microsoft is creating a mechanism in Visual Studio 2010 for deploying different configuration files for deployment and test   With that said  however  I have found that you in the ConnectionStrings section have a kind of placeholder called   DataDirectory    Maybe you could have a look at what s at work there     Here s a piece from machine config showing it     lt connectionStrings gt       lt add         name  LocalSqlServer          connectionString  data source   SQLEXPRESS Integrated Security SSPI AttachDBFilename  DataDirectory aspnetdb mdf User Instance true          providerName  System Data SqlClient        gt    lt  connectionStrings gt

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Inside  lt appSettings gt  you can create application keys    lt add key  KeyName  value  Keyvalue   gt    Later on you can access these values using    ConfigurationManager AppSettings  Keyname

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You have a couple of options  You could do this with a build   deploy step which would process your configuration file replacing your variables with the correct value    Another option would be to define your own Configuration section which supported this  For example imagine this xml    lt variableAppSettings gt    lt variables gt       lt add key   BaseDir  value  c  Programs Widget   gt    lt  variables gt    lt appSettings gt       lt add key  PathToDir  value   BaseDir Dir1   gt    lt  appSettings gt   lt  variableAppSettings gt    Now you would implement this using custom configuration objects which would handle replacing the variables for you at runtime

[c#] Variables within app.config/web.config

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