I’m a newbie in asp.net. I want to create my custom validation attribute to check, if a user with the same email exists. So, I need to assign an IUserService through the constructor and dependency injection. After that, I want to use the IUserService method in the validation method to check if the user already exists.

This is the code for my custom attribute.

[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false)]
public class EmailIsAlreadyExist : ValidationAttribute
{
    public new string ErrorMessage { get; set; }
    readonly IUserService _userService;

    public EmailIsAlreadyExist(IUserService userService) 
    {
        _userService = userService;
    }


    public override bool IsValid(object value)
    {
        string email = (string)value;

        if (_userService.CheckIfUserWithTheEmailIsAlreadyExist(email)) 
        {
            return false;
        }

        return true;
    }

    public override string FormatErrorMessage(string name)
    {
        return String.Format(CultureInfo.CurrentCulture,
          UserStringConstants.UserIsAlreadyExistErrorMessage, name);
    }
}

And I try to use my custom attribute here.

namespace WebApiForHikka.WebApi.Dto.Users;
public class UserRegistrationDto
{
    [EmailAddress(ErrorMessage = SharedStringConstants.EmailIsntFormatedCorrectlyErrorMessage)]
    [EmailIsAlreadyExist()]
    [Required]
    public required string Email { get; set; }

    [Required]
    [RegularExpression(UserStringConstants.SimplePasswordRegExpression, ErrorMessage = UserStringConstants.SimplePasswordErrorMessage)]
    public required string Password { get; set; }

    [Required]
    public required string Role { get; set; }
}

But I get an error which tells me that I don’t have a constructor with zero params.

By the way, all my dtos are in a liberary, because of it, I inject my dependency in a project for webApi controller.

So, is it possible to use dependency injection with a custom validation attribute?