Missing type map configuration or unsupported mapping

Question

Could somebody please explain what this error means? I have used automapper onces before but never had this kind of error.

Error

The server encountered an error processing the request. The exception message is 'Missing type map configuration or unsupported mapping. Mapping types: Char -> QuestionDto System.Char -> CollectiveDistributedPolling.QuestionDto Destination path: QuestionDto.Question1.Question1.Question10[0] Source value: R'.

Service1.svc.cs

public Service1() {
    Mapper.CreateMap<Question, QuestionDto>();
    Mapper.CreateMap<QuestionDto, Question>();
}

private Question MapToQuestion(QuestionDto q)
{
       return Mapper.Map<QuestionDto, Question>(q);
}

private QuestionDto MapToQuestionDto(Question q) <<< EXCEPTION GETS THROWN HERE
{
       return Mapper.Map<Question, QuestionDto>(q);
}

public QuestionDto ThrowQuestion(string user)
{
       return MapToQuestionDto(Database.GetInstance().ThrowQuestion(user));
}

IService1.cs

 [OperationContract]
        [WebInvoke(Method = "POST", BodyStyle = WebMessageBodyStyle.Wrapped, ResponseFormat = WebMessageFormat.Json)]
        QuestionDto ThrowQuestion(String user);

[DataContract]
    public class QuestionDto
    {
        [DataMember]
        public int ID { get; set; }
        [DataMember]
        public int next { get; set; }   
        [DataMember]
        public String question { get; set; }   
        [DataMember]
        public ICollection<QuestionDto> QuestionPhrase { get; set; } 
        [DataMember]
        public QuestionDto Next{ get; set; } 
        [DataMember]
        public ICollection<QuestionAnswerDto> QuestionAnswer { get; set; } 
        [DataMember]
        public ICollection<UserAnswerDto> UserAnswer { get; set; } 
    }

Question.cs

    public partial class Question
    {
        public Question()
        {
            this.QuestionPhrase = new HashSet<Question>();
            this.QuestionAnswer = new HashSet<QuestionAnswer>();
            this.UserAnswer = new HashSet<UserAnswer>();
        }

        public int ID { get; set; }
        public string question { get; set; }
        public Nullable<int> next { get; set; }

        public virtual ICollection<Question> QuestionPhrase { get; set; }
        public virtual Question Next { get; set; }
        public virtual ICollection<QuestionAnswer> QuestionAnswer { get; set; }
        public virtual ICollection<UserAnswer> UserAnswer { get; set; }
    }
}

Thanks to danludwig I could pinpoint the problem. It has something to do with

[DataMember]
public QuestionDto Next{ get; set; } 

But that mapping seems fine to me

Answer 1

This basically means AutoMapper is missing information about how to map from one property to another.

Though I can't tell by looking at the error, you can try the following process to figure out which property is missing the mapping. Start out by ignoring all of your destination type's properties:

Mapper.CreateMap<Question, QuestionDto>()
    .ForMember(d => d.ID, o => o.Ignore())
    .ForMember(d => d.next, o => o.Ignore())
    .ForMember(d => d.question, o => o.Ignore())
    .ForMember(d => d.QuestionPhrase, o => o.Ignore())
    .ForMember(d => d.Next, o => o.Ignore())
    .ForMember(d => d.QuestionAnswer, o => o.Ignore())
    .ForMember(d => d.UserAnswer, o => o.Ignore())
    // also ignore any other properties
;

Then, one by one, uncomment the ForMember lines until your exception is raised again. That is the property AM can't figure out how to map. I suspect is is in one of your collection properties...

Update

I'm wondering if perhaps there is a recursion problem going on here. Try this:

.ForMember(d => d.Next, o => o.ResolveUsing(s => {
    var tryToMap = Mapper.Map<QuestionDto>(s.Next); // exception here???
    return null;
}));

Not saying you have a data problem here, but if you did, you should expect AM to throw. If your question.Next == question, I imagine that AM would overflow the stack trying to map a property to it's owner over and over again.