Translate property name in error messages with FluentValidation - asp.net-core

Question

I use FluentValidation in my project in order to validate almost every requests coming into my WebApi.
It works fine, but I've been asked to translate property names in the error messages. My projet must handle at least french and english, so for example, what I want to achieve is :
'First Name' is required (english case)
'Prénom' est requis (french case)
I already have a IPropertyLabelService for other purposes, that is injected in the Startup.cs, that I want to use. It finds translations of property names in a .json, which already works fine.
My problem is that I don't know how to use it globally. I know that FluentValidation's doc says to set the ValidatorOptions.DisplayNameResolver in the Startup file, like this :
FluentValidation.ValidatorOptions.DisplayNameResolver = (type, memberInfo, expression) => {
// Do something
};
I don't know how I can use my IPropertyLabelService inside this, as the Startup.ConfigureServices method is not over yet, so I can't resolve my service...
Any other solution to achieve this behaviour is also more than welcome. I considered using .WithMessage() or .WithName() but I have a really big amount of validators, that would be really long to add this to all individually.

Answer 1

I answered this over on the FluentValidation issue tracker, but for completeness will include the answer here too:
Ssetting FluentValidation.ValidatorOptions.Global.DisplayNameResolver is the correct way to handle this globally (or you can use WithName at the individual rule level).
You need to ensure that this is set once, globally. If you need the service provider to have been initialized first, then make sure you call it at a point after the service provider has been configured (but ensure you still only set it once).
The "options" configuration mechanism in .NET Core allows you to defer configuration until after the point services have been constructed, so you can create a class that implements IConfigureOptions, which will be instantiated and executed during the configuration phase for a particular options type. FluentValidation doesn't provide any options configuration itself, so you can just hook into one of the built-in options classes (ASP.NET's MvcOptions is probably the simplest, but you can also use a different one if you're not using mvc).
For example, you could do something like this inside your ConfigureServices method:
public void ConfigureServices(IServiceCollection services) {
// ... your normal configuration ...
services.AddMvc().AddFluentValidation();
// Afterwards define some deferred configuration:
services.AddSingleton<IConfigureOptions<MvcOptions>, DeferredConfiguration>();
}
// And here's the configuration class. You can inject any services you need in its constructor as with any other DI-enabled service. Make sure your IPropertyLabelService is registered as a singleton.
public class DeferredConfiguration : IConfigureOptions<MvcOptions> {
private IPropertyLabelService _labelService;
public DeferredConfiguration(IPropertyLabelService labelService) {
_labelService = labelService;
}
public void Configure(MvcOptions options) {
FluentValidation.ValidatorOptions.Global.DisplayNameResolver = (type, memberInfo, expression) => {
return _labelService.GetPropertyOrWhatever(memberInfo.Name);
};
}
}