缺少类型映射配置或不支持的映射

Question

有人能解释一下这个错误是什么意思吗？我以前用过一次自动映射器，但从来没有出现过这种错误。

错误

服务器在处理请求时遇到错误。异常消息是“缺少类型映射配置或不支持的映射。映射类型：Char -> QuestionDto System.Char -> CollectiveDistributedPolling.QuestionDto 目标路径：QuestionDto.Question1.Question1.Question10[0] 源值：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; }
    }
}

感谢 danludwig，我可以查明问题所在。有关系

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

但我觉得这个映射很好

Answer 1

这基本上意味着 AutoMapper 缺少有关如何从一个属性映射到另一个属性的信息。

虽然我无法通过查看错误来判断，但您可以尝试以下过程来确定哪个属性缺少映射。首先忽略所有目标类型的属性：

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
;

然后，一一取消注释 ForMember 行，直到再次引发异常。那是属性 AM 无法弄清楚如何映射。我怀疑是在您的收藏属性之一中...

更新

我想知道这里是否存在递归问题。试试这个：

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

这里不是说你有数据问题，但如果你遇到了，你应该期待 AM 抛出。如果你的 question.Next == question，我想 AM 会溢出堆栈，试图一遍又一遍地将属性映射到它的所有者。