.NET: Which Exception to Throw When a Required Configuration Setting is Missing

configurationexceptionnet

Here's a standard scenario:

if(string.IsNullOrEmpty(Configuration.AppSettings["foobar"]))
   throw new SomeStandardException("Application not configured correctly, bozo.");

The problem is, I am not entirely certain which exception SomeStandardException should be.

I perused the 3.5 Framework and found two likely candidates: ConfigurationException and ConfigurationErrorsException.

System.Configuration.ConfigurationException

The exception that is thrown when a
configuration system error has
occurred.

Remarks

The
ConfigurationException exception is
thrown if the application attempts to
read or write data to the
configuration file but is
unsuccessful. Some possible reasons
for this can include malformed XML in
the configuration file, file
permission issues, and configuration
properties with values that are not
valid.

Note:

The ConfigurationException object is
maintained for backward compatibility.
The ConfigurationErrorsException
object replaces it for the
configuration system.

This exception actually sounds perfect for what I need, but it's been marked obsolete, so, ixnay on atthay.

This brings us to the thoroughly puzzling ConfigurationErrorsException:

System.Configuration.ConfigurationErrorsException

The current value is not one of the
EnableSessionState values.

As you can see, its documentation is completely useless. (It's that way in both local and online help.) An examination of the class itself shows that it's drastic overkill for what I want.

In a nutshell, I need a standard exception that should be thrown when an application configuration setting is missing or contains an invalid value. You'd think the Framework had such an exception baked into it for applications to use. (It apparently did, but it was marked obsolete, and was replaced by something much larger in scope.)

What solutions, if any, are you guys using for this, and am I going to have to suck it up and roll my own exception for this?

Edit Addenda

Some have asked whether or not I could provide a default value, and continue. In certain cases, yes, and in those cases, the exception would not be thrown. However, for certain settings, this won't apply. For instance: database server names and credentials, authentication servers, and paths to installed third party applications.

It is also worth noting that the application I'm primarily working on is a console application running in batch mode, and I want it to throw an exception that is caught by the main method and logged appropriately if the thing isn't appropriately configured. (It's legacy code I've inherited, and currently just assumes everything's peachy.)

Best Answer

Personally, I'd use InvalidOperationException, as it's a problem with the object state - not the configuration system. After all, shouldn't you allow these settings to be set by code and not config as well? The important part here is not that there was no line in app.config, but that a required piece of info was not present.

To me, ConfigurationException (and it's replacement, ConfigurationErrorsException - despite the misleading MSDN docs) are for errors in saving, reading, etc. of Configuration.

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