Can't inject service in ValidationAttribute

[sipi41]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Dear friends, yes, it's me again to bother you again! :-(

I love learning and found an article that woke up my mind, it was about creating a custom validation attribute (ValidationAttribute) but trying to inject a service (X) in order to get access to data or a method, etc... the idea sounds like a real project and I decided to give it a try... unfortunately every time I try to get a service I just get NULL... and yes, I tried to get some help from the MS help but the documentation is poor, no examples. (except a simple one where you learn how to override the IsValid method)

I created a simple class with a list of names and a method... the idea is that the Validation Attribute inject this as a service and then may ask the method if the name is valid or not... (if is on the list):

    public class NamesService
    {
        public List<string> Names { get; set; } = new() { "Guillermo", "Cinthy" };
        public bool IsAValidName(string Name) {
            return Names.Contains(Name);
        }
    }

Then I basically injected this as an Scoped service on my program.cs as follow:

builder.Services.AddScoped<NamesService>();

I did try to inject the service on a regular class and it works, also on a Blazor page and it works also... now, I created another class where I tried in 2 ways:

1. Using the IValidatableObject like this, and you can see I made a breakpoint and the value is NULL:

2. Ok, so I created a Custom Validation Attribute and the result is the same, like this:

Now I noticed several other options on the context, like:

• validationContext.InitializeServiceProvider
• validationContext.CreateAsyncScope

But no examples or what's the purpose or how to use these options? or will this help resolve the problem I'm facing?

Thank you for your help, this will help with what's being said all around... https://andrewlock.net/injecting-services-into-validationattributes-in-asp-net-core/

Expected Behavior

No response

Steps To Reproduce

No response

Exceptions (if any)

No response

.NET Version

6

Anything else?

No response

[MariovanZeist]

Hi @sipi41 it seems that Blazor doesn't support getting a service from a ValidationContext, the needed IServiceProvider is not supplied to the ValidationContext constructor
Here: and Here:

Looking at the code it shouldn't be too hard to implement, but there could have been good reasons not to, for example, because of the lack of async validation support, it wouldn't be possible to await a call to your server or database, forcing it to be a blocking call, blocking Blazor rendering and resulting in a bad user experience.

If you really need this functionality, you could create your own DataAnnotationsValidator class DataAnnotationsValidator.cs and inject a IServiceProvider into that class, and create your own extension methods EditContextDataAnnotationsExtensions.cs

duplicate of: #23380

[sipi41]

thank you @MariovanZeist it seems so difficult to implement... at least I never have done my own DataAnnotationsValidator, I think this is more commonly needed than I think, as in many real-life cases, interconnection is needed a lot.

I could instantiate my class with new, but will this be the preferred way instead? I mean, is there another way other than trying to re-do the .net framework?

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[pranavkm]

Description:
EnableDataAnnotationsValidation adds DataAnnotations validation support to an EditContext. The added instance currently does not configure the IServiceProvider on the DataAnnotations ValidationContext. This API change adds an additional overload that allows passing an instance of IServiceProvider that is then configured on the validation context.

static class EditContextDataAnnotationsExtensions
{
+ [Obsolete("This API is obsolete and will be removed in a future version")]
    public static IDisposable EnableDataAnnotationsValidation(this EditContext editContext)
+   public static IDisposable EnableDataAnnotationsValidation(this EditContext editContext, IServiceProvider serviceProvider)

Usage:

We generally don't expect user code to invoke this but use the component instead.

EditContext.EnableDataAnnotationsValidation(ServiceProvider);

Alternatives:

EditContext has a property bag that could be used to pass the IServiceProvider.