如何捕获配置绑定异常？

Question

I am building a console application in .NET Core 2.2.

I added strongly-typed configuration like this:

var configuration = new ConfigurationBuilder()
    .SetBasePath(Directory.GetCurrentDirectory())
    .AddJsonFile("appsettings.json", true)
    .AddCommandLine(args)
    .Build();

services.Configure<AppConfiguration>(configuration);

My configuration is bound to an object of class AppConfiguration . I wonder, how can I catch exceptions that could happen while binding config values to my class? For example, one of my configuration properties is an enum. If user provides nonexisting parameter, I get exception with stack trace:

at System.Enum.TryParseEnum(Type enumType, String value, Boolean ignoreCase, EnumResult& parseResult) at System.Enum.Parse(Type enumType, String value, Boolean ignoreCase) at System.ComponentModel.EnumConverter.ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, Object value)

Basically, I need some way to know that exception happened because of wrong configuration and not some other problem. If I was able to catch any configuration binding-related exceptions, I could throw my own WrongConfigurationException to catch it and be sure that something was wrong with config.

Answer 1

Fail early by eagerly getting/binding the desired object from configuration and catching any exceptions thrown during startup.

Reference Bind to an object graph

//...

var configuration = new ConfigurationBuilder()
    .SetBasePath(Directory.GetCurrentDirectory())
    .AddJsonFile("appsettings.json", true)
    .AddCommandLine(args)
    .Build();

try {
    //bind to object graph
    AppConfiguration appConfig = configuration.Get<AppConfiguration>();

    //custom validation can be done here as well
    //...        

    //if valid add to service collection.
    services.AddSingleton(appConfig);    
} catch(Exception ex) {
    throw new WrongConfigurationException("my message here", ex);
}

//...

Note that with the above example the class can be explicitly injected into dependents without having to be wrapped in IOptions<T> , which has its own design implications

The try-catch can also be foregone by just letting it fail at that point.

//...

var configuration = new ConfigurationBuilder()
    .SetBasePath(Directory.GetCurrentDirectory())
    .AddJsonFile("appsettings.json", true)
    .AddCommandLine(args)
    .Build();


//bind to object graph
AppConfiguration appConfig = configuration.Get<AppConfiguration>();

//custom validation can be done here as well
if(/*conditional appConfig*/)
    throw new WrongConfigurationException("my message here");

//if valid add to service collection.
services.AddSingleton(appConfig);    

//...

It should easily indicate where and why the exception was thrown.