-пофиксил добавление отзыва.

-добавил вывод информации о количестве зарегистрированных пользователях и количестве отзывов.

PhoneStore/Controllers/FeedbackController.cs

-using Microsoft.AspNetCore.Identity;
+using System.Linq;
 using Microsoft.AspNetCore.Mvc;
 using PhoneStore.Models;
 using PhoneStore.Services.Interfaces;
+using PhoneStore.ViewModels;
 using PhoneStore.ViewModels.Feedback;
 
 namespace PhoneStore.Controllers
 {
     public class FeedbackController : Controller
     {
-        private readonly UserManager<User> _userManager;
         private readonly IFeedbackService _feedbackService;
+        private readonly MobileContext _db;
 
-        public FeedbackController(
-            UserManager<User> userManager, 
-            IFeedbackService feedbackService)
+        public FeedbackController(IFeedbackService feedbackService, MobileContext db)
         {
-            _userManager = userManager;
             _feedbackService = feedbackService;
+            _db = db;
         }
 
-        [HttpGet]
-        public ActionResult<FeedbackViewModel> Create(FeedbackCreateViewModel model)
+        [HttpPost]
+        public IActionResult Create(FeedbackCreateViewModel model)
         {
             //TODO: валидация.
             var feedbackViewModel = _feedbackService.Create(model, User);
+            return PartialView("PartialViews/FeedbackPartialView", feedbackViewModel);
+        }
         
-            return Json(feedbackViewModel);
+        [HttpGet]
+        public ActionResult<FeedbackViewModel> GetCount()
+        {
+            var usersCount = _db.Users.Count();
+            var feedbacksCount = _db.Feedbacks.Count();
+            var model = new AccountingViewModel
+            {
+                User = new UserAccountingViewModel(nameof(User), usersCount),
+                Feedback = new FeedbackAccountingViewModel(nameof(Feedback), feedbacksCount)
+            };
+            return Json(model);
         }
     }
 }
\ No newline at end of file

PhoneStore/Helpers/FeedbackMapper.cs

@@ -13,6 +13,8 @@ namespace PhoneStore.Helpers
                 Text = self.Text,
                 PhoneId = self.PhoneId,
                 UserId = self.UserId,
+                User = self.User.MapToUserViewModel(),
+                Phone = self.Phone.MapToPhoneViewModel(),
                 CreationDateTime = self.CreationDateTime
             };
             return feedbackViewModel;

PhoneStore/ViewModels/AccountingViewModel.cs

+namespace PhoneStore.ViewModels
+{
+    public class AccountingViewModel
+    {
+        public UserAccountingViewModel User { get; set; }
+        public FeedbackAccountingViewModel Feedback { get; set; }
+    }
+
+    public class AccountingBase
+    {
+        public string EntityName { get; set; }
+        public int Count { get; set; }
+
+        public AccountingBase(string entityName, int count)
+        {
+            EntityName = entityName;
+            Count = count;
+        }
+    }
+
+    public class UserAccountingViewModel : AccountingBase
+    {
+        public UserAccountingViewModel(string entityName, int count) : base(entityName, count)
+        {
+        }
+    }
+    public class FeedbackAccountingViewModel : AccountingBase
+    {
+        public FeedbackAccountingViewModel(string entityName, int count) : base(entityName, count)
+        {
+        }
+    }
+}
\ No newline at end of file

PhoneStore/ViewModels/Feedback/FeedbackViewModel.cs

 using System;
 using PhoneStore.ViewModels.Account;
-using PhoneStore.ViewModels.Account;
 using PhoneStore.ViewModels.PhoneViewModels;
 
 namespace PhoneStore.ViewModels.Feedback

PhoneStore/Views/Shared/_Layout.cshtml

@@ -53,6 +53,16 @@
 <div class="container">
     <main role="main" class="pb-3">
         <div id="results"></div>
+        <button id="getData" class="btn btn-outline-warning">Получить данные</button>
+        <div id="widget">
+            <div class="alert alert-warning alert-dismissible fade show" role="alert">
+              <strong id="user"></strong> = <span id="usersCount"></span><br>
+              <strong id="feedback"></strong> = <span id="feedbacksCount"></span><br>
+              <button id="widgetClose" type="button" class="close" aria-label="Close">
+                <span aria-hidden="true">&times;</span>
+              </button>
+            </div>
+        </div>
         @RenderBody()
     </main>
 </div>

PhoneStore/wwwroot/js/site.js

 $(document).ready(function (){
+    $('#widget').hide();
     $('#search').on('keyup', function (e){
         e.preventDefault();
         let searchTerm = $(this).val();
@@ -11,7 +12,27 @@
 });
 
 $(document).ready(function (){
-    $("#feedbackForm").on("submit", function (e){
+    $('#getData').on('click', function (){
+        $('#widget').show();
+        $.ajax({
+            url: 'https://localhost:5001/feedback/getCount',
+            type: 'GET',
+            success: function (response) {
+                $('#user').text(response.user.entityName);
+                $('#usersCount').text(response.user.count);
+                $('#feedback').text(response.feedback.entityName);
+                $('#feedbacksCount').text(response.feedback.count);
+            }
+        });
+    });
+
+    $('#widgetClose').on('click', function (){
+        $('#widget').hide();
+    })
+});
+
+$(document).ready(function () {
+    $("#feedbackForm").on("submit", function (e) {
         e.preventDefault();
         let phoneId = $("input[name=phoneId]");
         let text = $("#text");
@@ -19,8 +40,12 @@ $(document).ready(function (){
             text: text.val(),
             phoneId: phoneId.attr('id')
         };
-        $.post('https://localhost:5001/feedback/create', feedback, function (response){
-            $('#feedbacks').before(response);
+        $.post('https://localhost:5001/Feedback/Create', feedback, function (response) {
+        }).done(function (response) {
+            $('#feedbacks').prepend(response);
+            text.text("");
+            return true;
         });
     });
 });
+