Does not contain definition for AddAsync()

Question

I am working on .Net razor pages. I have created a form on submit of form i am handling it using a post handler in .cs file but i am getting an error. I can add AddAsync in my handeler. Error is:-

Severity Code Description Project File Line Suppression State Error CS1061 'object' does not contain a definition for 'AddAsync' and no accessible extension method 'AddAsync' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?) youtubeproject C:\Users\lenovo\Desktop\MXN_INTERN\youtubeproject\youtubeproject\Pages\Categories\Create.cshtml.cs 22 Active

Here is my code of .cs file

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using youtubeproject.Model;
using youtubeproject.Data;

namespace youtubeproject.Pages.Categories
{
    public class CreateModel : PageModel
    {
        public readonly ApolicationDbContext _db;
        [BindProperty]
        public Category Category { get; set; }
        public CreateModel(ApolicationDbContext db)
        {
            _db = db;
        }
        public void OnGet()
        {
        }
        public async Task<IActionResult>OnPost()
        {
            await _db.Category.AddAsync(Category);
            await _db.SaveChangesAsync();
            return RedirectToPage("Index");

        }
    }


}