Developing Personalized Verification for Current Email in ASP.NET

Using Dependency Injection in ASP.NET Custom Validation Attributes

C# ASP.NET Core Implementation

[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false)]
public class EmailAlreadyExistsAttribute : ValidationAttribute
{
    private readonly IUserService _userService;
    public EmailAlreadyExistsAttribute() : base(() => ActivatorUtilities.CreateInstance<IUserService>(new HttpContextAccessor().HttpContext.RequestServices))
    {
        _userService = (IUserService)HttpContextAccessor().HttpContext.RequestServices.GetService(typeof(IUserService));
    }
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        string email = value as string;
        if (_userService.CheckIfUserWithTheEmailAlreadyExists(email))
        {
            return new ValidationResult(FormatErrorMessage(validationContext.DisplayName));
        }
        return ValidationResult.Success;
    }
}

Improving ASP.NET API Controllers to Allow Dependency-Injected Attributes

Configuration of C# ASP.NET Core Dependency Injection

public void ConfigureServices(IServiceCollection services)
{
    services.AddScoped<IUserService, UserService>();
    services.AddControllersWithViews(options =>
    {
        options.ModelMetadataDetailsProviders.Add(new ValidationProvider<IUserService>(services.BuildServiceProvider().GetService<IUserService>()));
    });
}
public class ValidationProvider<T> : IMetadataDetailsProvider where T : notnull
{
    private readonly T _service;
    public ValidationProvider(T service)
    {
        _service = service;
    }
    public void CreateValidationMetadata(ValidationMetadataProviderContext context)
    {
        context.ValidationMetadata.ValidatorProviders.Add(new InlineValidatorProvider(_service));
    }
}

ASP.NET Custom Validation FAQs

1. How does IUserService function with relation to custom validation attributes?
2. In most cases, IUserService is employed to work with user data. It's used in custom validation attributes to see if the database already contains a user with a particular email address.
3. Is it possible to utilize dependency injection in attribute constructors directly?
4. Because attribute constructors are metadata and are evaluated at build time rather than runtime, they do not directly allow dependency injection.
5. In ASP.NET Core, how can services be injected into an attribute?
6. By gaining access to the global service provider, services can be injected using the ActivatorUtilities to dynamically generate an instance of the service within the attribute.
7. Can singleton services be used inside validation attributes without risk?
8. Indeed, but only in the event that the service fails to maintain state. To be utilized safely within characteristics that may be accessed by multiple threads at once, singleton services need to be thread-safe.
9. Regarding addressing dependencies in custom validation attributes, what is the best approach?
10. Using indirect service resolution techniques, such as utilizing ActivatorUtilities or reaching out to the service provider via the HttpContext, is the recommended course of action. This keeps concerns apart and guarantees that features don't get attached to particular implementations.

Dependency Injection and Custom Validators: An Overview

The investigation of using dependency injection in ASP.NET custom validation features highlights the sophistication and potency of contemporary software development frameworks. When these functionalities are implemented well, the application becomes more stable and dependable and the developer's knowledge of ASP.NET's features and architectural subtleties is expanded. Developers may confidently understand these difficult topics and make sure that their apps can handle user input validation in a scalable and maintainable way by using the examples and talks that are provided.