The Best Way to Validate Your Settings in .NET 

How can this be implemented for options that need to be used to register other services? Is this validation performed when the services are built?

Would be neat if there were an additional fluent validation nuget package for this

I had started using it as it is quite easy to make a typo in your configuration. And more generally, I have found that self-checking code is just an awesome way to guard your solution any crazy spanner that your QA tester might throw at it. ;)

Still waiting for ConfigureAwait vid

I love the idea! But my attempt at implementation has failed due to Scoped services that cannot be resolved from root provider. I'm trying to figure out a way to get around this when not being done within a minimal api like in your example. Any ideas?

Hey Nick , can you make a video on how to write an exception middleware such that if any exception happens it should add it to output object and returns to the place where exception was thrown and continues execution

Thanks 👍

This looks like it would mix well with IValidatableObject does that happen automatically?

You would have that exception on startup if you registered the setting class as a singleton

Ungh... Back in my days, developers copied code only from verified sources, such as StackOverflow. Never from the official framework... ☹

I see you put your source code behind a paywall, which is fine. However, I can't in good conscience endorse Patreon usage to do so considering their immoral business practices. Also, would love to watch your videos on Rumble.

I understand the limitations of data annotations, but I really liked the beautiful simplicity of it. As soon as your started delving into Fluent Validation the code suddenly drowned in boilerplate. Thank you so much though, I will be using data annotation validation going forward!

This works if using the options in endpoints but it doesn't work if the options are needed during startup. Looks like ValidateOnStart() happens after ConfigureServices() and potentially after Configure(). Is there a way to validate earlier in the initialisation?

Why do you use AddOptions and Bind methods? There is an overload of Configure method which accepts IConfiguration

Any idea how to address the issue that when you inject an IOptions, if you haven't configured it, you get a default instance with all properties with their default value. Even if your setting object has required properties. For example, you end up with a null string that wasn't nullable and required.

I think it would also be interesting to see how to have a similar effect when options change. For example if you have settings within an Azure Vault and you would like to validate it as soon as it changes? Clearly this is no longer possible on application startup as application is already running, however it would be interesting to react immediately (if even possible?) and do something (log it or send email etc). It would be nice to see an additional video for solving such a problem :)

I'm doing this but it's a bit different. My AppSettings class as a Validate() function and I have an IStartupFilter which runs that function. In the end provides the same functionality i.e. throw a list of errors for any invalid settings on startup.

It looks like fluent validation is still the best approach in .NET 8.

Wish an example would have been shown of using it with asynchrous code, like validating that an API key is valid as he had mentioned. Also would the validation logic be re-called if the settings are reloaded with the other option patterns (IOptionsMonitor I believe)?

You are the best, even better than chat gpt

I always wanted to make a code generator to auto create json schema for an option class so you get validation and auto complete.

Very interesting. I always learn a lot from watching your videos, although I usually have to watch them a few times as there is so much information in such a short space of time. I would love to know how this technique could be implemented when using the named IOptions pattern.

❤ it. Thank you Nick. Now I'm battling with build time settings and secrets and how to validate those. Further down the rabbit hole we go.

I get stuck on terminology of options, as it's not an option they are settings within configuration. A section has configuration settings ...any reason why they called it options? On top of that is the default providers after configuration is instantiated. I think there are 7 default providers. I always clear then, and add back the provider I need

Sadly, it doesn't work for non-host apps like Azure Function or Aws Lambda.

Honestly... Both design are horrible. An object should not exist in an invalid state. You can create simpler types that have the proper types (LogLevel enum, a type representing an int range or just using an unsigned int)... And handle reading the options as a deserialization problem. Goal is to remove boilerplate and have explict types.

This cannot be done in an Azure Function App since it doesn’t use the Hosting package. Any workaround?

Hey Nick ! :) For thanks sharing this technique, i use to manage all my checks with DataAnnotations but i can understand that sometimes FluentValidation could be better for more complex case ^^ Juste have one questions on it, would you're technique also for "hot reload settings" case ? 🤔

Right on lunchtime 👌

I hate that to bind options i have to pass the config object. I wanted a way to do it using the registerd IConfiguration so i had to create me own extension methods to do that. imo that should be out of the box, idk why you wouldn't want your IConfiguration in your Iservicecollection so that you can inject it as needed and define more services (such as options) that are based on that.

How to add data annotation for a string that take http/https endpoint as a setting , to validate using ValidateDataAnnotations()

But what if a string is entered into the Retries field instead of a number? How can we check for this case, since the error will occur during binding?

What would be the solution do turn this off if it is on "developer machine" ?

I get why people don't use it. Looks really annoying

Love your videos. Never stop making them ))

This is going over my head. It tried but didn't understand why it is used.

i will incorporate this into my current project, this could save me headaches later

I love this approach. Thanks for sharing.

Very nice..Lot of good things learning from you..

I particularly like putting both the configuration and validation of options in their own class. Microsoft did a good job when they designed the options library/pattern for .NET.

This is very very good! Thanks Nick

Why not simply create an extension method that supports: var configSection = configuration.GetSection("key"); services.Configure(configSection); var settings= new T(); configSection.Bind(settings); settings.Validate(); Where T is of type IValidate and contains a Validate method.

Like the approach using FluentValidation over attributes personally. Options Pattern is really powerful, if a bit dense for something so important (and at the same time so un-exciting) to a project setup. I have tended to follow a similar approach with a validator (today explicit, maybe next time ill look at using FV), but not using the OnStartup bit as it is out of my control. Instead I cause validation to occur prior to the host Run so that I can log individual events for bad configuration bits and not just get the exception/stack trace output. Combine all that with using postconfigure for some options to smart-default or otherwise derive values and its a bunch for work for sure - but work that leads to a polished end result.

Also would not it be nice to have appsettings in C# and load them dynamically on startup? Would that be possible ?

Hats off Nick Chapsas!

Awesome!

Very cool!

Fantasic, is there a place where I can find the code you showed us in this video?

Awesome content as usual!

Why not put the validation in the init methods themselves and throw exceptions?

First

Nice and clear way to validate settings 👌. Thanks Man

Very useless to much work

Even validation at start time is too late IMHO. Validation should be done in the text editor while the user types in the values. Also there should be the IntelliSense suggestions and tooltips when hovering your mouse on top of the parameter names. This is achievable with schemas. I've been using XML schemas (xsd.exe) for my settings for more than a decade now. There was just no other alternative for the functionality I've described. But now JSON schema seems to be catching up with XSD, so the setting validation/documentation should also start using the schema and provide the validation/IntelliSense at edit time. But while we are not there yet this video is very helpful, thank you!

Hi Nick! Small heads up; theres a typo in the description “settions” presumably in stead of “settings” Cheers

booooooooooooooooooring !

One of the worst decisions I made was using Fluent validations instead of Data Annotation in a project. Strongly recommend not using them, just creates unnecessary boilerplate that leads to people not using simple validations because it requires too much. code and the validation is separate from your domain so it's much harder to figure out required rules. Not to mention that any sort of generation (OpenAI) is not native and requires extra setup.