An error occurred while updating the entries - entity-framework

Question

I'm strugglish with adding feature for my controller. While adding new item, receving the error like: "An error occurred while updating the entries. See the inner exception for details."
I debugged it, and understood ProductDetailIs is null and here is the issue. But, can not figure out how to mend the problem.
Here is the DTO models:
public class WishlistItemDto
{
public int Id { get; set; }
public string CustomerId { get; set; }
public ProductDetailsDtoWithPrimaryImage ProductDetails { get; set; }
public int Quantity { get; set; }
}
public class WishListItemCreationDto
{
public string CustomerId { get; set; }
public int ProductDetailId { get; set; }
public int Quantity { get; set; }
}
Controller:
[HttpPost]
public async Task<IActionResult> Add(WishListItemCreationDto wishListItemDto)
{
var itemAdd = _mapper.Map<WishlistItemDto>(wishListItemDto);
var itemCreated = await _wishListItemService.AddAsync(itemAdd);
return CreatedAtAction(nameof(GetId), new { id = itemCreated.Id }, wishListItemDto);
}
Service:
public async Task<WishlistItemDto> AddAsync(WishlistItemDto item)
{
var entity = _mapper.Map<WishlistItem>(item);
await _wishListItemRepository.AddAsync(entity);
return _mapper.Map<WishlistItemDto>(entity);
}
Repository:
public async Task<WishlistItem> AddAsync(WishlistItem item)
{
await _context.Set<WishlistItem>().AddAsync(item);
await _context.SaveChangesAsync();
return item;
}

Answer 1

This line here:
var itemAdd = _mapper.Map<WishlistItemDto>(wishListItemDto);
your "wishListItemDto" is passed in as a 'WishListItemCreationDto' which contains only a ProductDetailsId. Automapper will have no way of knowing how to convert that into a ProductDetailsDtoWithPrimaryImage.
Typically for something like this where you pass an reference ID you would compose your entity by either populating a FK or loading the referenced entity. Your existing service and repository patterns will complicate your final solution. From what I can see from your example I'd look at creating an AddAsync method that accepts the WishListItemCreationDto:
public async Task<WishlistItemCreationDto> AddAsync(WishlistItemCreationDto item)
{
var entity = _mapper.Map<WishlistItem>(item);
var productDetails = _productDetailsRepository.GetById(item.ProductDetailsId);
entity.ProductDetails = productDetails;
await _wishListItemRepository.AddAsync(entity);
return _mapper.Map<WishlistItemDto>(entity);
}
Without the added abstraction complexity of the Service and Repository the add operation can be a whole lot simpler:
[HttpPost]
public async Task<IActionResult> Add(WishListItemCreationDto wishListItemDto)
{
// or better, use an injected dependency to the Context...
// TODO: add applicable exception handling.
using(var context = new AppDbContext())
{
var item = _mapper.Map<WishlistItem>(wishListItemDto);
var productDetails = context.ProductDetails.Single(x => x.ProductDetailsId == wishListItemDto.ProductDetailsId);
item.ProductDetails = productDetails;
context.SaveChanges();
return CreatedAtAction(nameof(GetId), new { id = itemCreated.Id }, wishListItemDto);
}
}