Instance cannot be tracked because another instance with the same key is already tracked

Question

I just started with asp.net core MVC by developing a Car Rental application and I'm using EF Core for working with the database. The problems comes when I'm trying to update a record from database. It gives me the folloing exception:

InvalidOperationException: The instance of entity type 'Car' cannot be tracked because another instance with the same key value for {'CarID'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see the conflicting key values.

Here's my code for updating a car:

Repository:

public Car GetCarByID(int carId)
{
    return _context.Cars.Where(c=> c.CarID == carId).Include(c=>c.Category)
                                                    .Include(c=>c.Type)
                                                   .Include(c=>c.CarLocations).ThenInclude(c=>c.Location)
                                                   .FirstOrDefault();
}

 public void UpdateCar(Car car)
 {
     _context.Update(car);
 }

Controller car update code:

 [HttpGet]
        public async Task<IActionResult> Edit(int id)
        {
            await SeedCarView();

            var carToEdit = _carsRepo.GetCarByID(id);

            if (carToEdit == null)
            {
                return NotFound();
            }

            return View(carToEdit);
        }

[HttpPost]
        public async Task<IActionResult> Edit(Car car)
        {
            await SeedCarView();

            if (ModelState.IsValid)
            {
                /*get selections from dropdown form*/
                string categSelection = Request.Form["Category_Name"].ToString();
                string bodySelection = Request.Form["TypeName"].ToString();
                var selectedLocations = Request.Form["AreChecked"].ToList();

                var selectedCategory = await _categoriesRepo.GetCategoryByIDAsync(categSelection);
                var selectedBodyType = await _typesRepo.GetBodyTypeByNameAsync(bodySelection);

                car.Category = selectedCategory;
                /*Increment the number of cars in this category*/
                car.Category.NumberOfCars = car.Category.Cars.Count + 1;
                car.Type = selectedBodyType;

                foreach (var sel in selectedLocations)
                {
                    CarLocation carLocation = new CarLocation
                    {
                        Car = car
                    };

                    var location = _locationsRepo.GetLocationByID(Int32.Parse(sel));
                    carLocation.Location = location;

                    car.CarLocations.Add(carLocation);
                }

                _carsRepo.UpdateCar(car);
                await _carsRepo.SaveAsync();

                return RedirectToAction("Listing");
            }

            return View(car);
        }


private async Task SeedCarView()
        {
            var categories = await _categoriesRepo.GetCategoriesAsync();
            var bodyTypes = await _typesRepo.GetBodyTypesAsync();
            var locations = await _locationsRepo.GetLocationsAsync();

            List<string> categorieNames = new List<string>();
            List<string> typeNames = new List<string>();

            /*get the existing categories name and body types name*/
            foreach (var item in categories)
                categorieNames.Add(item.Category_Name);
            foreach (var item in bodyTypes)
                typeNames.Add(item.Name);

            ViewBag.Category_Names = categorieNames;
            ViewBag.TypeNames = typeNames;
            ViewBag.LocationNames = locations;
        }

Here's the Service Configuration methode:

public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllersWithViews();
            services.AddDbContext<CarRentalContext>(item => item.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));
            services.AddScoped<ICarsRepository, CarsRepository>();
            services.AddScoped<ICarCategoryRepository, CarCategoryRepository>();
            services.AddScoped<ICarTypeRepository, CarTypeRepository>();
            services.AddScoped<ILocationsRepository, LocationsRepository>();
        }

Exception at Update methode

Please help me to fix this issue. I'm stuck at this for more than 2 days and I don't understand where's the problem.

Update:

I've changed my Update methode in Repository with the following code:

 public void UpdateCar(Car car)
        {
            var existingCar = GetCarByID(car.CarID);
            _context.Entry(existingCar).CurrentValues.SetValues(car);

            //_context.Update(car);
        }

and the code in the POST action:

    foreach (var sel in selectedLocations)
                {
                    var location = _locationsRepo.GetLocationByID(Int32.Parse(sel));

                    CarLocation carLocation = new CarLocation
                    {
                        CarID = car.CarID,
                        LocationID = location.Location_ID,
                        Car = car,
                        Location = location
                    };

                    car.CarLocations.Add(carLocation);
                }

but now only the car instance is updated, without childs like CarCategory, Locations and CarType.

The way you did it you should not use context.Update(), you just need to update whatever you need and then do SaveChanges(). Reason being - when you getting data using EF, by default it is tracking the instances for changes - that's exactly what it is saying to you, when you do .Update(), all it does - it internally adds object for tracking into EF, but you already have same object tracked cause you got it already without NoTracking option — Nikita Chayka
I tried to get the instance with AsNoTracking() but it gives me the same exception. — John
Currently this is definately the problem i see, so could you please either remove your call to Update and do SaveChanges() or do AsNoTracking and update your code with exact error again. Other possibility here- how exactly you creating context? Is it PerRequest mode in dependency cotainer? Or you creating it somehow else ? Please provide here the details — Nikita Chayka
When I'm removing the Update call, nothing happens, the record is not updated and if I add the AsNoTracking I'm getting the same exception. I will add the service configuration in the question imediatly — John
Hm, interesting, can you just for experiment then comment out this line - car.CarLocations.Add(carLocation). — Nikita Chayka

John John · Accepted Answer · 2021-04-26T19:44:10

I solved the the exception by creating a new instance of the Car, cleaning its old data and adding the changed properties.

public async Task<IActionResult> Edit(Car car)
        {
            await SeedCarView();

            if (ModelState.IsValid)
            {
                /*get selections from dropdown form*/
                string categSelection = Request.Form["Category_Name"].ToString();
                string bodySelection = Request.Form["TypeName"].ToString();
                var selectedLocations = Request.Form["AreChecked"].ToList();

                var selectedCategory = await _categoriesRepo.GetCategoryByIDAsync(categSelection);
                var selectedBodyType = await _typesRepo.GetBodyTypeByNameAsync(bodySelection);

                var carToBeUpdated = _carsRepo.GetCarByID(car.CarID);
                carToBeUpdated.CarLocations.Clear();

                foreach (var sel in selectedLocations)
                {
                    var location = _locationsRepo.GetLocationByID(Int32.Parse(sel));

                    CarLocation carLocation = new CarLocation
                    {
                        CarID= car.CarID,
                        LocationID = location.Location_ID,
                        Car = car,
                        Location = location
                    };

                    carToBeUpdated.CarLocations.Add(carLocation);
                }

                carToBeUpdated.Category = selectedCategory;
                carToBeUpdated.CategoryName = categSelection;
                /*Increment the number of cars in this category*/
                carToBeUpdated.Category.NumberOfCars = carToBeUpdated.Category.Cars.Count + 1;
                carToBeUpdated.Type = selectedBodyType;
                carToBeUpdated.TypeID = selectedBodyType.TypeID;
                carToBeUpdated.Acceleration = car.Acceleration;
                carToBeUpdated.ClimateControll = car.ClimateControll;
                carToBeUpdated.Fabrication_Date = car.Fabrication_Date;
                carToBeUpdated.FuelType = car.FuelType;
                carToBeUpdated.Model = car.Model;
                carToBeUpdated.PictureURL = car.PictureURL;
                carToBeUpdated.TransmisionType = car.TransmisionType;
                carToBeUpdated.PricePerDay = car.PricePerDay;

                //_carsRepo.UpdateCar(carToBeUpdated);
                await _carsRepo.SaveAsync();

                return RedirectToAction("Listing");
            }

            return View(car);
        }

Instance cannot be tracked because another instance with the same key is already tracked

1 Answers