Unable to save changes to database using SaveChangesAsync()

For some reason database will not update a post, even though it navigates to right page which suggests that it should have saved the changes. Here's my code below. Note: I tried this with EF, now using repository pattern and still the same issue.

public class PostsController : Controller
{
    public IRepository _repo;

    public PostsController(IRepository repo)
    {
        _repo = repo;  
    }
    public IActionResult Index()
    {
        return View();
    }

    public IActionResult Post()
    {
        return View();
    }

    [HttpGet]
    public IActionResult Edit()
    {
        return View(new Post());
    }
    [HttpPost]
    public async Task<IActionResult> Edit(Post post)
    {
        _repo.AddPost(post);

        if (await _repo.SaveChangesAsync())
            return RedirectToAction("Index");
        else
            return View(post);
    }
}

Once I create a post, the page navigates to Index which is suggesting that SaveChanges(); is working without exceptions. However if I view my Db, it's not there!

Here's my db context just inc. :

public class ApplicationDbContext : 
    IdentityDbContext<ApplicationUser, 
                      ApplicationRole, 
                      string,
                      IdentityUserClaim<string>, 
                      IdentityUserRole<string>, 
                      IdentityUserLogin<string>,
                      IdentityRoleClaim<string>, 
                      IdentityUserToken<string>>
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options)
    {
    }

    public DbSet<Post> Posts { get; set; }
}

And here's my repository clearly implementing db context:

private ApplicationDbContext _context;

public Repository(ApplicationDbContext context)
{
    _context = context;
}

Here's my repository and irepository code as well as my configure services from startup.cs.:

Repository.cs:

{
    public class Repository : IRepository
    {
        private ApplicationDbContext _context;

        public Repository(ApplicationDbContext context)
        {
            _context = context;
        }


        public void AddPost(Post post)
        {

            _context.Posts.Add(post);
        }

        public List<Post> GetAllPosts(int id)
        {
            return _context.Posts.ToList();
        }

        public Post GetPost(int id)
        {
            return _context.Posts.FirstOrDefault(p => p.Id == id);
        }

        public void RemovePost(int id)
        {
            _context.Posts.Remove(GetPost(id));
        }


        public void UpdatePost(Post post)
        {
            _context.Posts.Update(post);
        }

        public async Task<bool> SaveChangesAsync()
        {
            if (await _context.SaveChangesAsync() > 0)
            {
                return true;
            }
            return false;
        }
    }
}

Here's my irepository.cs

{
    public interface IRepository
    {
        Post GetPost(int id); 
        List<Post> GetAllPosts(int id);

        void AddPost(Post post);
        void UpdatePost(Post post);
        void RemovePost(int id);

        Task<bool> SaveChangesAsync();

    }
}

Here's my configure services code

 public void ConfigureServices(IServiceCollection services)
    {

        services.Configure<CookiePolicyOptions>(options =>
        {
            // This lambda determines whether user consent for non-essential cookies is needed for a given request.
            options.CheckConsentNeeded = context => true;
            options.MinimumSameSitePolicy = SameSiteMode.None;
        });

        services.AddDbContext<ApplicationDbContext>(options =>
            options.UseSqlServer(
                Configuration.GetConnectionString("DefaultConnection")));

        services.AddIdentity<ApplicationUser, ApplicationRole>()
            .AddEntityFrameworkStores<ApplicationDbContext>();
        services.AddTransient<IRepository, Repository>();

        services.AddMvc(config =>
        {
            // using Microsoft.AspNetCore.Mvc.Authorization;
            // using Microsoft.AspNetCore.Authorization;
            var policy = new AuthorizationPolicyBuilder()
                             .RequireAuthenticatedUser()
                             .Build();
            config.Filters.Add(new AuthorizeFilter(policy));
        });

My post.cs entity is here:

{
public class Post
{
    public int Id { get; set; }
    [Required(ErrorMessage = "Title is required")]
    public virtual string Title { get; set; } = "";
    public virtual string Short_Description { get; set; }
    public string Image { get; set; } = "";

    [DataType(DataType.MultilineText)]
    public virtual string Content { get; set; }

    public DateTime Posted { get; set; } = DateTime.Now;
    public DateTime? Modified { get; set; } = DateTime.Now;
}

}