Why an automapper is throwing exception that complex type cannot be constructed in linq?

Question

I have created an automapper

CreateMap<Records_Log, Records_LogDto>()
                .ForMember(dest => dest.UserName, opt =>
                {
                    opt.ResolveUsing(d => d.User.UserName);
                });

Records_Log

public class Records_Log
    {
        public int Id { get; set; }
        public string Table_name { get; set; }



        [ForeignKey("Records")]
        public int RecordsId { get; set; }
        public Records Records { get; set; }
        public  int RecordId { get; set;  }
        public string OldValue { get; set; }
        public string NewValue { get; set; }

        [ForeignKey("User")]
        public string UserId { get; set; }
        public ApplicationUser User { get; set; }

        public DateTime ChangeDate { get; set; }

        public string Action { get; set; }


    }

Records_LogDto

public class Records_LogDto
    {

        public int Id { get; set; }
        public string Table_name { get; set; }

        public int RecordsId { get; set; }
        public Records Records { get; set; }

        public int RecordId { get; set; }
        public string OldValue { get; set; }
        public string NewValue { get; set; }

        public string UserId { get; set; }

        public string UserName { get; set; }

        public string Action { get; set; }

        public DateTime ChangeDate { get; set; }
    }

Records:

public class Records
    {
        public int Id { get; set; }

        public string SerialName { get; set; }

        public string RecordsName { get; set; }

        public string Url { get; set; }
        public string AttachmentPath { get; set; }
        public string ImagePath { get; set; }

        public string RecordsNameModified { get; set; }

        public bool isDeleted { get; set; }

        public bool isRead { get; set; }

        public bool IsHidden { get; set; }
        public bool MarkAsImportant { get; set; }
        public string ImportantComments { get; set; }

        public int subTypeID { get; set; }


        public virtual ICollection<Records_Rate> Records_Rate { get; set; }

    }

My query

var query = (from st in db.Records_State
                         join sl in db.Records_Log
                         on st.Records.Id equals sl.RecordsId
                         where st.Records.isDeleted
                         && sl.Table_name == nameof(Records)
                         && sl.Action == "Deleted"
                         && sl.NewValue == "Top"
                         && (string.IsNullOrEmpty(recordsName) || sl.Records.RecordsName.Contains(recordsName)
                            || sl.Records.RecordsNameModified.Contains(recordsName))
                         && (fromDate == null || sl.ChangeDate >= fromDate)
                         && (toDate == null || sl.ChangeDate <= toDate)
                         orderby sl.ChangeDate descending
                         select new Records_Log { 
                             Records= st.Records, 
                             ChangeDate= sl.ChangeDate 
                         })
                         .AsQueryable();

   



query = from p in query
                group p by p.Records.Id
                into pGroup
                orderby pGroup.Key
                select pGroup.FirstOrDefault();

        var result = query.Skip((pageNumber - 1) * pageSize)
          .Take(pageSize)
          .OrderByDescending(st => st.Id);

        var dto = Mapper.Map<List<Records_LogDto>>(result);

now in the last line var dto = Mapper.Map<List<Records_LogDto>>(result); it throws exception:

Error mapping types.\r\n\r\nMapping types:\r\nDbQuery1 -> List1\r\nSystem.Data.Entity.Infrastructure.DbQuery1[[PortalBackEndAPI.Models.Records_Log, PortalBackEndAPI.Core, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]] -> System.Collections.Generic.List1[[PortalBackEndAPI.Dto.Records_LogDto, PortalBackEndAPI, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]"}

and

The entity or complex type 'PortalBackEndAPI.Models.Records_Log' cannot be constructed in a LINQ to Entities query

Answer 1

The object you pass into the map method is still of Type DBQuery which Automapper has no configured mapping for. The error code hints at this! The reason why the object you are passing is not of the type Records_Log is because you didn't let it resolve yet.

Check if you can call a ToList or ToListAsync method on the DBQuery like in the following example.

var dto = Mapper.Map<List<Records_LogDto>>(result.ToList());
// Or
var dto = Mapper.Map<List<Records_LogDto>>(await result.ToListAsync());

One of those methods (There are others) will force the DBQuery to be resolved and loaded into a List.