Question

Somehow my code doesn’t work any more (it did work before with the exact same code). This is the problem:

The code

I’m trying to map some objects to ViewModels with this code:

Configuration:

Mapper.CreateMap<BookcaseItem, FoundBookcaseItemViewModel>()
    .ForMember(x => x.Title, opt => opt.MapFrom(src => src.Book.Title))
    .ForMember(x => x.Authors, opt => opt.MapFrom(src => src.Book.Authors.Select(x => x.Name).Aggregate((i, j) => i + ", " + j)))
    .ForMember(x => x.Identifiers, opt => opt.MapFrom(src => (!string.IsNullOrEmpty(src.Book.Isbn10) ? ("ISBN10: " + src.Book.Isbn10 + "\r\n") : string.Empty) +
                                                                (!string.IsNullOrEmpty(src.Book.Isbn13) ? ("ISBN13: " + src.Book.Isbn13) : string.Empty)))
    .ForMember(x => x.Pages, opt => opt.MapFrom(src => src.Book.Pages))
    .ForMember(x => x.ImageUri, opt => opt.MapFrom(src => src.Book.ThumbnailUriSmall));

The usage:

public ActionResult Index()
{
    string facebookId = _accountService.GetLoggedInUserFacebookId();

    IEnumerable<BookcaseItem> items = _bookcaseItemService.GetBookcaseItemsForUser(facebookId);
    IEnumerable<FoundBookcaseItemViewModel> viewModels = items.Select(Mapper.Map<BookcaseItem, FoundBookcaseItemViewModel>);

    return PartialView(viewModels);
}

The error

This results in the following error:

An exception of type ‘AutoMapper.AutoMapperMappingException’ occurred in AutoMapper.dll but was not handled in user code

The debug data

First of all I ensure that there are no configuration errors by calling:

Mapper.AssertConfigurationIsValid();

I’ve set breakpoints all over my code and try to debug it, but I can’t make sense of it. The ‘items’ collection is filled with data (proxy classes generated by Entity Framework), but the the ‘viewModels’ collection is filled with strange data. It has a ‘message’ that says this:

Mapping types:
BookcaseItem_B9B52593B2659AC05C47AB2A6E0F7AEA9989CC34D3527DF5B6AA988ED57166FB
-> String System.Data.Entity.DynamicProxies.BookcaseItem_B9B52593B2659AC05C47AB2A6E0F7AEA9989CC34D3527DF5B6AA988ED57166FB
-> System.String

Destination path: FoundBookcaseItemViewModel.Authors

Source value:
System.Data.Entity.DynamicProxies.BookcaseItem_B9B52593B2659AC05C47AB2A6E0F7AEA9989CC34D3527DF5B6AA988ED57166FB

And then there’s a stacktrace property that says:

at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()

at System.Linq.SystemCore_EnumerableDebugView`1.get_Items()

Oh and finally there’s another property called ‘context’ with the following data:

Can anyone explain what’s going on here and why my code isn’t working any longer? I did a couple of changes to my solution recently, but I’ve rolled them back by Git, so they shouldn’t have any effect on the code.

My setup

• Visual Studio 12 RC
• ASP.NET MVC 4
• .NET Framework 4.0 (I had 4.5 but that caused too many errors, so I rolled back with Git to version 4.0)
• Entity Framework 5.0 RC
• AutoMapper 2.1.267

The entity and ViewModel

I don’t know if it’s relevant, but here is the source class for the mapping:

public class BookcaseItem : Entity
{
    public Guid Id { get; set; }
    public bool IsRenting { get; set; }
    public bool IsSwapping { get; set; }
    public bool IsSelling { get; set; }
    public decimal RentingPrice { get; set; }
    public decimal SellingPrice { get; set; }
    public string Currency { get; set; }
    public bool IsAvailable { get; set; }
    public virtual Guid BookId { get; set; }
    public virtual Guid UserId { get; set; }

    public virtual Book Book { get; set; }
    public virtual User User { get; set; }

    public BookcaseItem()
    {
        IsAvailable = true;
        Currency = "USD";
    }
}

And this is the destination class for the mapping:

public class FoundBookcaseItemViewModel
{
    public Guid Id { get; set; }
    public bool IsRenting { get; set; }
    public bool IsSwapping { get; set; }
    public bool IsSelling { get; set; }
    public decimal RentingPrice { get; set; }
    public decimal SellingPrice { get; set; }
    public string Title { get; set; }
    public string Authors { get; set; }
    public string Identifiers { get; set; }
    public int Pages { get; set; }
    public string ImageUri { get; set; }
}

Answer 1

It seems like there is a problem with mapping Authors property. This Aggregate call will throw an exception if the Authors sequence is null or empty.

.ForMember(x => x.Authors, 
           opt => opt.MapFrom(src => src.Book.Authors.Select(x => x.Name).Aggregate((i, j) => i + ", " + j)))