Automapper 在同一张表的外键上遇到问题

Question

我遇到了一些自动映射器问题。

将Mapper.AssertConfigurationIsValid(); 添加到我的代码后，我收到以下错误：

The following property on CollectiveDistributedPolling.AnswerDto cannot be mapped: 
    Answer
Add a custom mapping expression, ignore, add a custom resolver, or modify the destination type CollectiveDistributedPolling.AnswerDto.
Context:
    Mapping to property Answer from System.Int32 to CollectiveDistributedPolling.AnswerDto
    Mapping to property QuestionAnswer from CollectiveDistributedPolling.QuestionAnswer to CollectiveDistributedPolling.QuestionAnswerDto
    Mapping to property QuestionAnswer from System.Collections.Generic.ICollection`1[[CollectiveDistributedPolling.QuestionAnswer, CollectiveDistributedPolling, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]] to System.Collections.Generic.List`1[[CollectiveDistributedPolling.QuestionAnswerDto, CollectiveDistributedPolling, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]
    Mapping from type CollectiveDistributedPolling.Question to CollectiveDistributedPolling.QuestionDto
Exception of type 'AutoMapper.AutoMapperConfigurationException' was thrown.

所以有一个错误将答案映射到 AnswerDto，但映射应该是直截了当的（见下文）

[DataContract]
    public class AnswerDto
    {
        [DataMember]
        public int ID { get; set; }
        [DataMember]
        public string answer { get; set; }
        [DataMember]
        public List<QuestionAnswerDto> QuestionAnswer { get; set; }
        [DataMember]
        public List<UserAnswerDto> UserAnswer { get; set; }
    }

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

        public int ID { get; set; }
        public string answer { get; set; }

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

映射

Mapper.CreateMap<Question, QuestionDto>();
Mapper.CreateMap<QuestionDto, Question>();

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

这是问题的SQL 表。如您所见，从 Question(next) 到 Question(ID) 存在外键约束。

这是我的 Model.edmx

的一部分

如果您还有其他问题，请提出。

Answer 1

看起来 EF 与 DTO 一起工作的方式可能会导致 AutoMapper 大失所望。请记住，使用 AutoMapper，您可以在逐个属性的基础上准确指定要执行的操作。

例如，离开this question，你可以尝试这样的事情：

// target = QuestionDto, source = Question
Mapper.CreateMap<Question, QuestionDto>()
      .ForMember(target => target.ID, options => options.MapFrom(source => source.ID));

你也可以告诉AutoMapper忽略Next，在映射后直接处理：

 Mapper.CreateMap<Question, QuestionDto>()
       .ForMember(target => target.Next, options => options.Ignore())
       .AfterMap(source, target => {
           // do some magic here
           // source = Question, target = QuestionDto
       });

或者，您可以完全切换并尝试遵循the answer to this question，它建议使用ValueInjecter 来展平/取消展平DTO，而不是Automapper：

使用http://valueinjecter.codeplex.com/，它会进行扁平化和非扁平化，以及您需要的任何其他内容，下载中有一个 asp.net mvc 示例应用程序，其中演示了所有功能（也是单元测试）