Automapper expression must resolve to top-level member

Question

I am using automapper to map source and destination objects. While I map them I get the below error.

Expression must resolve to top-level member. Parameter name: lambdaExpression

I am not able resolve the issue.

My source and destination objects are:

public partial class Source
{
        private Car[] cars;

        public Car[] Cars
        {
            get { return this.cars; }
            set { this.cars = value; }
        }
}

public partial class Destination
{
        private OutputData output;

        public OutputData Output
        {            
            get {  return this.output; }
            set {  this.output= value; }
        }
}

public class OutputData
{
        private List<Cars> cars;

        public Car[] Cars
        {
            get { return this.cars; }
            set { this.cars = value; }
        }
}

I have to map Source.Cars with Destination.OutputData.Cars object. Could you please help me in this?

Answer 1

You are using :

 Mapper.CreateMap<Source, Destination>()
 .ForMember( dest => dest.OutputData.Cars, 
             input => input.MapFrom(i => i.Cars)); 

This won't work because you are using 2 level in the dest lambda.

With Automapper, you can only map to 1 level. To fix the problem you need to use a single level :

 Mapper.CreateMap<Source, Destination>()
 .ForMember( dest => dest.OutputData, 
             input => input.MapFrom(i => new OutputData{Cars=i.Cars})); 

This way, you can set your cars to the destination.

Answer 2

1. Define mapping between Source and OutputData.

   Mapper.CreateMap<Source, OutputData>();
   

2. Update your configuration to map Destination.Output with OutputData.

   Mapper.CreateMap<Source, Destination>().ForMember( dest => dest.Output, input => 
       input.MapFrom(s=>Mapper.Map<Source, OutputData>(s))); 
   

Answer 3

You can do it that way:

// First: create mapping for the subtypes
Mapper.CreateMap<Source, OutputData>();

// Then: create the main mapping
Mapper.CreateMap<Source, Destination>().
    // chose the destination-property and map the source itself
    ForMember(dest => dest.Output, x => x.MapFrom(src => src)); 

That's my way to do that ;-)

Answer 4

The correct answer given by allrameest on this question should help: AutoMapper - Deep level mapping

This is what you need:

Mapper.CreateMap<Source, Destination>()
    .ForMember(dest => dest.OutputData, opt => opt.MapFrom(i => i));
Mapper.CreateMap<Source, OutputData>()
    .ForMember(dest => dest.Cars, opt => opt.MapFrom(i => i.Cars));

When using the mapper, use:

var destinationObj = Mapper.Map<Source, Destination>(sourceObj)

where destinationObj is an instance of Destination and sourceObj is an instance of Source.

NOTE: You should try to move away from using Mapper.CreateMap at this point, it is obsolete and will be unsupported soon.