How to make custom validation with Tag Helper?

Question

How to make custom validation with Tag Helper? (ASP MVC NET6)

I have this Registration Class like below:

public class Registration  
{          
        [Required]  
        [EmailAddress]  
        [Display(Name = "User Email Address")]  
        public string userEmail { get; set; } = "";  
  
  
  
I need to check to a user table (Users), if the emailAddress already exists or not  
  
  
internal static bool IsEmailExists(string emailAddress)  
bool isExists = false;  
...  
...  
  
return isExists  

Answer 1

Hi, @Dondon510

I suggest you to use RemoteAttribute to achieve this, you can refer to this simple demo：

remote method

[AcceptVerbs("Get", "Post")]  
    [AllowAnonymous]  
    public async Task<IActionResult> IsEmailInUse(string email)  
    {  
        //check if the emailAddress already exists or not in database  

        var user =await _dbContext.users.Where(x => x.Email == email).FirstOrDefaultAsync();  
        if (user == null)  
        {  
            return Json(true);  
        }  
        else  
        {  
            return Json($"Email {email} is already in use");  
        }  
    }  

Then add remote attribute in your model

         [Required]  
         [EmailAddress]  
         [Display(Name = "User Email Address")]  
         [Remote(action:"IsEmailInUse",controller:"Home")]  
         public string userEmail { get; set; }  

Now, When you type email in <input/>,It will check if the emailAddress already exists or not

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Best regards,
Xinran Shen