How to add Validation in Asp.net core form | Data Annotation in asp.net core| validate form

Hello & As-salam u alikum ! , In this article we will learn to validate the form fields in asp.net core.
Note : For Beginner Guide Articles :

https://dotnetcorecommunity.blogspot.com/p/aspnet-core-tutorials-paracticals.html

Step# 1:  

Watch previous article for creating a new record and upload Image  in asp.net core 

https://dotnetcorecommunity.blogspot.com/2019/10/how-to-add-new-records-in-sql-server.html

Step# 2:  

 Go to the model folder ---> tbl_user  and add the following annotations that I have added below.

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;

namespace WebApplication7.Models
{
    public partial class TblUser
    {
        public TblUser()
        {
            TblComments = new HashSet<TblComments>();
            TblFriendListFlReceiverNavigation = new HashSet<TblFriendList>();
            TblFriendListFlSenderNavigation = new HashSet<TblFriendList>();
            TblPost = new HashSet<TblPost>();
            TblPostsLiked = new HashSet<TblPostsLiked>();
            TblVerificationcode = new HashSet<TblVerificationcode>();
        }
        [Key]
        public int UId { get; set; }

        [Display(Name ="Email")]
        [RegularExpression(@"^([\w\.\-]+)@([\w\-]+)((\.(\w){2,3})+)$", ErrorMessage ="Invalid Email")]
        [StringLength(50,ErrorMessage ="Email Should be less than 50 characters or greater than 7 characters",
         MinimumLength = 15)]
        [Required(ErrorMessage ="*")]
        public string UEmail { get; set; }

        [Display(Name = "Password")]
        [Required(ErrorMessage = "*")]
        public string UPassword { get; set; }


        [Required(ErrorMessage = "*")]
        [Display(Name = "Name")]
     
        [StringLength(25, ErrorMessage = "Name Should be less than 50 characters or greater than 7 characters",
         MinimumLength = 3)]
        public string UUserName { get; set; }

        [Display(Name = "Profile Picture")]
        public string UProfilePicture { get; set; }
        
        [Display(Name = "Added Date")]
        [Required(ErrorMessage = "*")]
        public DateTime? UAddedDate { get; set; }

        [Display(Name = "Modified Date")]

        public DateTime? UModifiedDate { get; set; }

        [Display(Name = "Is Login")]
        [Required(ErrorMessage = "*")]
        public int? UIsuserlogin { get; set; }
        [Display(Name = "Is Approved")]
        [Required(ErrorMessage = "*")]
        public int? UIsuseraproved { get; set; }

        public virtual ICollection<TblComments> TblComments { get; set; }
        public virtual ICollection<TblFriendList> TblFriendListFlReceiverNavigation { get; set; }
        public virtual ICollection<TblFriendList> TblFriendListFlSenderNavigation { get; set; }
        public virtual ICollection<TblPost> TblPost { get; set; }
        public virtual ICollection<TblPostsLiked> TblPostsLiked { get; set; }
        public virtual ICollection<TblVerificationcode> TblVerificationcode { get; set; }
    }
}

Step# 3:  

Go to the controller and add the following condition: 
this condition will let your code execute when every field value is fine and validated.

     [HttpPost]
        public async Task<IActionResult>  Create(TblUser ui, IFormFile file)
        {
            if (ModelState.IsValid)
            {

            
            TblUser u = new TblUser();
            if (file == null || file.Length == 0)
            {
                u.UProfilePicture = "noimage.png";
            }
            else
            {
                string filename = System.Guid.NewGuid().ToString() + ".jpg";
                var path = Path.Combine(
                            Directory.GetCurrentDirectory(), "wwwroot", "img", filename);

                using (var stream = new FileStream(path, FileMode.Create))
                {
                    await file.CopyToAsync(stream);
                }

                u.UProfilePicture = filename;

            }


          
            u.UUserName = ui.UUserName;
            u.UPassword = ui.UPassword;
            u.UAddedDate = DateTime.Now;
            u.UIsuseraproved = ui.UIsuseraproved;
            u.UIsuserlogin = ui.UIsuserlogin;
            u.UEmail = ui.UEmail;
             db.TblUser.Add(u);
            await db.SaveChangesAsync();
            return RedirectToAction("Index");
            }
            else
            {
                return View();
            }
        }

Step# 4:  

Run the application and submit the button with wrong and blank input fields.You will find the errors as shown below.