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?

Sofiasofie

Could you add automapper configuration? – Sassy

I tried to add the configuration, it throws error while running the configurations. My configuration looks as below Mapper.CreateMap<Source, Destination>().ForMember( dest => dest.OutputData.Cars, input => input.MapFrom(i => i.Cars)); Expression 'dest => dest.OutputData.Cars' must resolve to top-level member. Parameter name: lambdaExpression – Sofiasofie

This worked for me: Mapper.CreateMap<Destination, Source>().ForMember(x => x.Cars, x => x.MapFrom(y => y.OutputData.Cars)).ReverseMap(); (also posted in an answer below) – Molybdenous

#15555288 related – Screenplay

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.

Alabaster

Also used this solution for mapping between objects where the source had string somethingKey and string somethingValue, and the destination had object something { string Key, string Value } – Semiweekly

Greate Answer!! – Pragmatics

Answer 2

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 ;-)

Catalpa

This is the best solution – Perren

Works perfect when you want map IDataRecord to complex DTO. – Gomulka

A much more elegant way, compared to the most voted answer, which could lead to some very convoluted syntax. – Constantinople

Answer 3

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))); 
   

Sassy

I have field in the OutputData which has some default value. I don't have a mapping for this field in the source. So I didn't map it. After mapping is done, my default value is set to null value on the destination. How to avoid it setting to a null value. – Sofiasofie

Answer 4

ForPath works for this exact scenario.

Mapper.CreateMap<Destination, Source>().ForPath(dst => dst.OutputData.Cars, e => e.MapFrom(src => src.Cars));

Mullis

Answer 5

This worked for me:

Mapper.CreateMap<Destination, Source>()
    .ForMember(x => x.Cars, x => x.MapFrom(y => y.OutputData.Cars))
    .ReverseMap();

Molybdenous

Answer 6

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.

Mooch