Repeating Configuration across Referenced Assemblies

Question

Let's say we have Assembly1 and Assembly2.

Assembly2 is a C# class library used by Assembly1.

Web and Service References are configured and stored in Asembly2/app.Config.

Moreover, the EF connection string(s) are in Assembly2/app.Config.

When I use Assembly2 in Assembly1, the Assembly2 config file is not used. In fact, in that scenario, only the Assembly1 configuration appears accessible through default means.

As a result, I have to copy the Assembly2 config contents into the Assembly1 config.

This has worked for me for many projects.

Is there another way? A better way?

It seems wrong to have repeating configuration data.

Do you have a recommendation or technique that works?

Thank you.

Answer 1

You need to apply changes to the config file of entry point exe assembly. Class library assembly (dll) config files are never used. They are made by Visual Studio so you could easily copy the settings to exe config files if needed.

Bellow is example of the config file for exe assembly that has both, settings from class library ClassLibrary1 and settings from the exe assembly MainAssembly. You can see that both connection strings are in one connectionStrings settings. However, if you need to set other settings, beside connection string, you need to add extra section.

If you are already using this technique, this is correct way to go. This technique is flexible. For example if you have more than one project having the same connection strings on one box, you could specify the connection strings in machine.config file. You can also override the settings in some projects if needed.

<?xml version="1.0"?>
<configuration>
  <configSections>
    <sectionGroup name="applicationSettings"
                  type="System.Configuration.ApplicationSettingsGroup, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" >

      <!--This section declaratrion pasted here from dll conifg file -->
      <section name="ClassLibrary1.Properties.Settings"
               type="System.Configuration.ClientSettingsSection, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
               requirePermission="false" />

      <!--This section declaratrion was here in the first place -->
      <section name="MainAssembly.Properties.Settings"
               type="System.Configuration.ClientSettingsSection, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
               requirePermission="false" />
    </sectionGroup>
  </configSections>
  <connectionStrings>

    <!--This connection string was here in the first place -->
    <add name="MainAssembly.Properties.Settings.MainAssemblyConnectionString"
         connectionString="MainConnectionStringValue" />

    <!--This connection string pasted here from dll config file -->
    <add name="ClassLibrary1.Properties.Settings.LibraryConnectionString"
         connectionString="LibraryConnectionStringValue"
         providerName="" />
  </connectionStrings>
  <applicationSettings>

    <!--This settings section pasted here from dll config file -->
    <ClassLibrary1.Properties.Settings>
      <setting name="LibrarySetting"
               serializeAs="String">
        <value>LibrarySettingValue</value>
      </setting>
    </ClassLibrary1.Properties.Settings>

    <!--This strings section was here in the first place -->
    <MainAssembly.Properties.Settings>
      <setting name="MainAssemblySetting"
               serializeAs="String">
        <value>MainSettingValue</value>
      </setting>
    </MainAssembly.Properties.Settings>
  </applicationSettings>
</configuration>

Answer 2

A DLL (or another referenced assembly) is not meant to carry it's own app.config, but rather have everything configured by the caller. So everything should go into the app.config of the exe.

Consider for example a shared data access library that needs connection strings to the database. The library should be possible to use from a variety of applications with different connection requirements. Having the connection string tied strictly to the shared library wouldn't work, it has to be done at the client using the library.

It is possible to put systemwide settings that affect all applications running on a machine in the machine.config file, but use that approach with caution as it will affect all applications on the machine.