Automapper expression mapping

Question

I am trying to perform the following Automapper mapping for an OrderBy:

Expression<Func<ServerObject, object>> serverQueryable = x => x.TestEnumKVP.Value;
Mapper.Map<Expression<Func<ServerObject, object>>, Expression<Func<DatabaseObject, object>>(serverQueryable)

I want to map the ServerObject expression to a DatabaseObject expression

ServerObject defined as:

public class ServerObject
{
    public KeyValuePairEx TestEnumKVP { get; set; }
}

KeyValuePairEx is a wrapper for the Enumeration which stores the Int16 value and the string value:

public enum TestEnum : Int16 { Test1, Test2, Test3 }

public class KeyValuePairEx
{
    internal KeyValuePairEx(TestEnum key, string value) { }

    public TestEnum Key { get; set; }
    public string Value { get; set; }
}

DatabaseObject defined as:

public class DatabaseObject
{
    public string TestEnumId { get; set; }
}

The Mapping I have is:

AutoMapper.Mapper.Initialize(config =>
{
    config.CreateMap<DatabaseObject, ServerObject>().ForMember(dest => dest.TestEnumKVP.Value, opt => opt.MapFrom(src => src.TestEnumId));
});

The mapping fails with:

'Expression 'dest => dest.TestEnumKVP.Value' must resolve to top-level member and not any child object's properties. Use a custom resolver on the child type or the AfterMap option instead.'

I need ServerObject.TestEnumKVP.Value to Map to DatabaseObject.TestEnumId. I am aware that Expression mappings are reversed - hence why the Map is from DatabaseObject to ServerObject. I have spent many hours on this and am at a loss as to how to get the mapping to work!

NB. I am using AutoMapper 6.1.1

Any help would be appreciated!

sjr sjr · Accepted Answer · 2017-08-22T08:30:22

Thank you Lucian, I followed the github link and the solution offered by Blaise has worked. See below:

CreateMap<DatabaseObject, ServerObject>().ForMember(dest => dest.TestEnumKVP, opt => opt.MapFrom(src => src));
CreateMap<DatabaseObject, KeyValuePairEx>().ForMember(dest => dest.Value, opt => opt.MapFrom(src => src.TestEnumId));

I was starting to look for at workarounds so delighted it was possible and that the solution was so clean and concise.

Thanks again!

Automapper expression mapping

2 Answers