How to validate if email attribute is unique in an ASP .NET CORE API?

Question

I was needing to make a post or put a validation on the server side to check if the email is unique.

In the research I have always done the example was a traditional MVC application and never an api.

In many cases I saw that the [Remote] https://learn.microsoft.com/pt-br/aspnet/core/mvc/models/validation?view=aspnetcore-2.2#remote-attribute . I tried to implement according to the documentation, but debugging verified that the function in the controller is neither called.

User.cs

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using Microsoft.AspNetCore.Mvc;

namespace Base.Models
{
    [Table("users")]
    public partial class User
    {
        ...
        [Required]
        [EmailAddress]
        [Remote(action: "VerifyEmail", controller: "UserController",ErrorMessage="Email already in use")]
        [Column("email", TypeName = "varchar(254)")]
        public string Email { get; set; }
        ...
    }
}

UserController.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using Base.Models;

namespace Base.Controllers
{
    [Route("api/users")]
    [ApiController]
    public class UserController : Controller
    {
        ...
        [AcceptVerbs("Get")]
        public IActionResult VerifyEmail(string email)
        {
            //forcing it to go wrong
            return Json($"Email {email} is already in use.");
        }
        ...
    }
}

Anyone have any idea how to implement this?

manzapanza · Accepted Answer · 2020-03-07 18:41:59Z

9

Seeing that it was not progressing, I decided to do a personalized validation.

EmailUserUniqueAttribute.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.ComponentModel.DataAnnotations;
using Base.Models;

namespace Core.Models
{
    public class EmailUserUniqueAttribute : ValidationAttribute
    {
        protected override ValidationResult IsValid(
            object value, ValidationContext validationContext)
        {
            var _context = (AppDbContext)validationContext.GetService(typeof(AppDbContext));
            var entity = _context.Users.SingleOrDefault(e => e.Email == value.ToString());

            if (entity != null)
            {
                return new ValidationResult(GetErrorMessage(value.ToString()));
            }
            return ValidationResult.Success;
        }

        public string GetErrorMessage(string email)
        {
            return $"Email {email} is already in use.";
        }
    }
}

User.cs

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using Microsoft.AspNetCore.Mvc;

namespace Base.Models
{
    [Table("users")]
    public partial class User
    {
        ...
        [Required]
        [EmailAddress]
        [EmailUserUnique]
        [Column("email", TypeName = "varchar(254)")]
        public string Email { get; set; }
    }
}
        ...

It works, but I don't know if this is the best way to do this.

edited Mar 7, 2020 at 18:41

manzapanza

6,2914 gold badges43 silver badges51 bronze badges

answered Jun 12, 2019 at 19:28

Adriano Faria Alves

1772 silver badges7 bronze badges

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2 Comments

SwampyFox Over a year ago

This is a fine and reusable way to do this validation. When I saw this, I was looking to see that you found the "GetService" method on the validation context. This method is a good example of "Service Locator" that is often considered an Anti-Pattern. However, because of the way DI works with validation filters, it is perfectly pragmatic to use.

Pushpa Kumara Over a year ago

This was really helpful. Easy to customize. Thank you for the answer.

Elias K. · Accepted Answer · 2019-06-12 17:11:04Z

1

I cant comment cause I lack the sufficient reputation, and if I had time I would had gone and verified but I think your issue here is the [Route("api/users")]. You are giving your decorator the Controller name but that controller is behind a different route. Easy debug of that will be to remove the Route temporarily OR put the "VerifyEmail" action to another controller that you arent altering its route.

answered Jun 12, 2019 at 17:11

Elias K.

1641 silver badge5 bronze badges

1 Comment

Adriano Faria Alves Over a year ago

Thanks for the help, but I have already tested it with no route and it did not work, I think this Remote is only for client side validation.

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