Merging runtime-created section config with system config - configuration

Question

I am using the EntLib in an environment where database connection strings are retrieved from a separate library call that decrypts a proprietary config file. I have no say over this practice or the format of the config file.
I want to do EntLib exception logging to the database in this setting. I therefore need to set up a EntLib database configuration instance with the name of the database, with the connection string. Since I can't get the connection string until run time, but EntLib does allow run-time configuration, I use the following code, as described in this:
builder.ConfigureData()
.ForDatabaseNamed("Ann")
.ThatIs.ASqlDatabase()
.WithConnectionString(connectionString)
.AsDefault();
The parameter connectionString is the one I've retrieved from the separate library.
The sample code goes on to merge the created configuration info with an empty DictionaryConfigurationSource. I, however, need to merge it with the rest of the configuration code from the app.config. So I do this:
var configSource = new SystemConfigurationSource();
builder.UpdateConfigurationWithReplace(configSource);
EnterpriseLibraryContainer.Current
= EnterpriseLibraryContainer.CreateDefaultContainer(configSource);
... which is based very closely on the sample code.
But: I get an internal error in Microsoft.Practices.EnterpriseLibrary.Common.Configuration.SystemConfigurationSource.Save. The failing code is this:
var fileMap = new ExeConfigurationFileMap { ExeConfigFilename = ConfigurationFilePath };
var config = ConfigurationManager.OpenMappedExeConfiguration(fileMap, ConfigurationUserLevel.None);
config.Sections.Remove(section);
config.Sections.Add(section, configurationSection);
config.Save();
... where 'section' is "connectionStrings". The code fails on the Add method call, saying that you can't add a duplicate section. Inspection shows that the connectionStrings section is still there even after the Remove.
I know from experience that there's always a default entry under connectionStrings when the configuration files are actually read and interpreted, inherited from the machine.config. So perhaps you can never really remove the connectionStrings section.
That would appear to leave me out of luck, though, unless I want to modify the EntLib source, which I do not.
I could perhaps build all the configuration information for the EntLib at run time, using the fluent API. But I'd rather not. The users want their Operations staff to be able to make small changes to the logging without having to involve a developer.
So my question, in several parts: is there a nice simple workaround for this? Does it require a change to the EntLib source? Or have I missed something really simple that would do away with the problem?

Answer 1

I found a workaround, thanks to this post. Rather than taking the system configuration source and attempting to update it from the builder, I copy the sections I set up in app.config into the builder, and then do an UpdateConfigurationWithReplace on an empty dummy configuration source object in order to create a ConfigurationSource that can be used to create the default container.
var builder = new ConfigurationSourceBuilder();
var configSource = new SystemConfigurationSource();
CopyConfigSettings("loggingConfiguration", builder, configSource);
CopyConfigSettings("exceptionHandling", builder, configSource);
// Manually configure the database settings
builder.ConfigureData()
.ForDatabaseNamed("Ann")
.ThatIs.ASqlDatabase()
.WithConnectionString(connectionString)
.AsDefault();
// Update a dummy, empty ConfigSource object with the settings we have built up.
// Remember, this is a config settings object for the EntLib, not for the entire program.
// So it doesn't need all 24 sections or however many you can set in the app.config.
DictionaryConfigurationSource dummySource = new DictionaryConfigurationSource();
builder.UpdateConfigurationWithReplace(dummySource);
// Create the default container using our new ConfigurationSource object.
EnterpriseLibraryContainer.Current
= EnterpriseLibraryContainer.CreateDefaultContainer(dummySource);
The key is this subroutine:
/// <summary>
/// Copies a configuration section from the SystemConfigurationSource to the ConfigurationSourceBuilder.
/// </summary>
/// <param name="sectionName"></param>
/// <param name="builder"></param>
/// <param name="configSource"></param>
private static void CopyConfigSettings(string sectionName, ConfigurationSourceBuilder builder, SystemConfigurationSource configSource)
{
ConfigurationSection section = configSource.GetSection(sectionName);
builder.AddSection(sectionName, section);
}