AutoMapper and nested object mappings for encapsulation

Question

I'm not too familiar with automapper, but it's been thrown on me by our Software Architect for this project.

The concept is complete encapsulation of volatility. Here's a poorly made Diagram

API/Presentation Layer | Request and Response suffixed objects. (ie, ApplicationCreateRequest)

Business Layer | Home of Domain transfer objects, suffixed DTO. (ie, ApplicationCreateDTO)

Database Layer | Home of Resource Access Objects and entities suffixed RAO and Entity (ie, ApplicationEntity, ApplicationCreateRAO)

I need to convert ApplicationCreateRequests to ApplicationCreateDTO's, as well as convert the Requests Nested objects to DTO's as well.

For example:

public class ApplicationCreateRequest
{
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public ContactCreateRequest Contact { get; set; }
    public DemographicCreateRequest Demographic { get; set; }
    public EducationCreateRequest Education { get; set; }
    public WorkCreateRequest Work { get; set; }
}

becomes

public class ApplicationCreateDTO
{
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public ContactCreateDTO Contact { get; set; }
    public DemographicCreateDTO Demographic { get; set; }
    public EducationCreateDTO Education { get; set; }
    public WorkCreateDTO Work { get; set; }
}

The DTO's and Requests have for the most part the same properties.

I've only gotten to work with very basic mappings such as:

CreateMap<ObjectOne, ObjectTwo>();

Minus Minus · Accepted Answer · 2018-11-09T21:00:29

A easy way to map complex model is to declare, and map them from easiest (with native types eg : strings, int,...) to complex ones.

So, you should create simple mappings for ContactCreateRequest to ContactCreateDTO with CreateMap (and others simplest). Then you will have to create something like :

MapFrom allows you to specify the property (a reason beeing if named differently) to map from. It also allows you to specify a result from a pre-defined mapping, you simply tell it the member you want to Map from...

Mapper.CreateMap<ApplicationCreateRequest, ApplicationCreateDTO>()
    .ForMember(g => g.FirstName, opt => opt.MapFrom(src => src.FirstName));
    .ForMember(g => g.LastName, opt => opt.MapFrom(src => src.LastName));
    .ForMember(g => g.Contact, opt => opt.MapFrom(src => Mapper.Map<ContactCreateRequest,ContactCreateDTO>(g.Contact)));
    .ForMember(g => g.Demographic, opt => opt.MapFrom(src => Mapper.Map<DemographicCreateRequest,DemographicCreateDTO>(g.Demographic)));
    .ForMember(g => g.Education, opt => opt.MapFrom(src => Mapper.Map<EducationCreateRequest,EducationCreateDTO>(g.Education)));
    .ForMember(g => g.Work, opt => opt.MapFrom(src => Mapper.Map<WorkCreateRequest,WorkCreateDTO>(g.Work)));

You can build up by using

.ForMember(g => g.Property, opt => opt.Ignore()); // to ignore the mapping of a property

Handy note, define base mapping before complex ones, otherwise you will have trouble!

AutoMapper and nested object mappings for encapsulation

1 Answers