Question

I cant find the reason why Automapper cannot construct my MailDTO class (for what I think).
Here is the code:

Model Entity:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using System.Runtime.Serialization;
using Project1.Model;

namespace Project1.Entities
{
    [DataContract(Name = "Mail", Namespace = "http://site.com/1.0/Mail")]
    public class Mail : Message, Project1.Entities.IMail
    {
        public Mail() { ... }

        public Mail(mail mailValue) { ... }

        public Mail(mail mailValue, long UserID, bool includereplies) { ... }

        public Mail(mail mailValue, int gmtTimeZone, long UserID) { ... }


        long m_MailID;

        [DataMember(Order = 0)] 
        public long MailID
        {
            get { return m_MailID; }
            set { m_MailID = value; }
        }

        long? m_ParentID;

        [DataMember(Order = 1)]
        public long? ParentID
        {
            get { return m_ParentID; }
            set { m_ParentID = value; }
        }

        List<Mail> m_Replies = new List<Mail>();

        [DataMember(Order = 2)]
        public List<Mail> Replies
        {
            get { return m_Replies; }
            set { m_Replies = value; }
        } 
    }
}  

DTO – part:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.Serialization;

namespace Project1.DTO
{
    [DataContract(Name = "MailDTO")]
    public class MailDTO
    {
        [DataMember(Order = 0)]
        public long MailID { get; set; }
        [DataMember(Order = 1)]
        public long? ParentID { get; set; }
        [DataMember(Order = 2)]
        public string MessageValue { get; set; }

        [DataMember(Order = 3)]
        public long SourceUser { get; set; }
        [DataMember(Order = 4)]
        public string CreatedDate { get; set; }
        [DataMember(Order = 5)]
        public List<long> Recipients { get; set; }
        [DataMember(Order = 6)]
        public List<MailDTO> Replies { get; set; }

        public MailDTO(Project1.Entities.Mail mail)
        {
            MailID = mail.MailID;
            ParentID = mail.ParentID;
            MessageValue = mail.MessageValue;
            SourceUser = mail.SourceUser.UserID;
            CreatedDate = mail.CreatedDate.Value.ToString();
            Replies = mail.Replies.Select(item => new MailDTO(item)).ToList();
        }
    }
}  

Client side:

[WebInvoke(UriTemplate = "RetrieveMail?mailID={mailID}", Method = "POST", ResponseFormat = WebMessageFormat.Json, RequestFormat = WebMessageFormat.Json)]
public Project1.DTO.MailDTO RetrieveMail(Project1.Entities.UserSession details, long mailID)
{
    Project1.Logic.IMessageComponent svc = Project1.Logic.ConfigAndResourceComponent.Container().Resolve<Project1.Logic.IMessageComponent>();
    Project1.Entities.Mail item = svc.RetrieveMail(details, mailID); // Return data is fine, no problem here
    Project1.DTO.MailDTO converted = Mapper.Map<Project1.Entities.Mail, Project1.DTO.MailDTO>(item); // The error goes here
    return converted;
}

Global.asax.cs:

Mapper.CreateMap<Project1.Entities.Mail, Project1.DTO.MailDTO>();
Mapper.CreateMap<Project1.Entities.Mail, Project1.DTO.MailDTO>().ForMember(dest => dest.SourceUser, opt => opt.MapFrom(src => src.SourceUser.UserID));
Mapper.CreateMap<Project1.Entities.Mail, Project1.DTO.MailDTO>().ForMember(dest => dest.CreatedDate, opt => opt.MapFrom(src => src.CreatedDate.Value.ToString()));
Mapper.CreateMap<Project1.Entities.Mail, Project1.DTO.MailDTO>().ForMember(dest => dest.Recipients, opt => opt.MapFrom(src => src.Recipients.Select(item => item.UserDetail.UserID).ToList()));
Mapper.CreateMap<Project1.Entities.Mail, Project1.DTO.MailDTO>().ForMember(dest => dest.Replies, opt => opt.MapFrom(src => src.Replies.Select( item => new Project1.DTO.MailDTO(src)).ToList()));
Mapper.AssertConfigurationIsValid();  

Error encountered:

Type 'Project1.DTO.MailDTO' does not have a default constructor


Trying to map Project1.Entities.Mail to Project1.DTO.MailDTO.
Using mapping configuration for Project1.Entities.Mail to Project1.DTO.MailDTO
Exception of type 'AutoMapper.AutoMapperMappingException' was thrown


  at System.Linq.Expressions.Expression.New(Type type)
   at AutoMapper.DelegateFactory.<>c__DisplayClass1.<CreateCtor>b__0(Type t)
   at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
   at AutoMapper.DelegateFactory.CreateCtor(Type type)
   at AutoMapper.Mappers.ObjectCreator.CreateObject(Type type)
   at AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.CreateObject(ResolutionContext context)
   at AutoMapper.Mappers.TypeMapObjectMapperRegistry.NewObjectPropertyMapMappingStrategy.GetMappedObject(ResolutionContext context, IMappingEngineRunner mapper)
   at AutoMapper.Mappers.TypeMapObjectMapperRegistry.PropertyMapMappingStrategy.Map(ResolutionContext context, IMappingEngineRunner mapper)
   at AutoMapper.Mappers.TypeMapMapper.Map(ResolutionContext context, IMappingEngineRunner mapper)
   at AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.Map(ResolutionContext context)  

I guess the problem is because of this:

public List<MailDTO> Replies { get; set; } // Collects MailID and UserID + other details

Before it was:

public List<long> Replies { get; set; }  // Collects MailID

And it work fine, but I have to change it because of added information.
Anyone can help me solve the error? Thanks a lot.

Answer 1

Add a default constructor to the MailDTO class

public MailDTO() { }

AutoMapper needs a default constructor to create an instance first; before it can then copy values into the properties. The only constructor defined on MailDTO in your code is one which takes a Project1.Entities.Mail instance; which AutoMapper doesn’t know how to fire.