Reverse Mapping and Unflattening

Starting with 6.1.0, AutoMapper now supports richer reverse mapping support. Given our entities:

public class Order {
  public decimal Total { get; set; }
  public Customer Customer { get; set; } 
}
public class Customer {
  public string Name { get; set; }
}

We can flatten this into a DTO:

public class OrderDto {
  public decimal Total { get; set; }
  public string CustomerName { get; set; }
}

We can map both directions, including unflattening:

Mapper.Initialize(cfg => {
  cfg.CreateMap<Order, OrderDto>()
     .ReverseMap();
});

By calling ReverseMap, AutoMapper creates a reverse mapping configuration that includes unflattening:

var customer = new Customer {
  Name = "Bob"
};
var order = new Order {
  Customer = customer,
  Total = 15.8m
};

var orderDto = Mapper.Map<Order, OrderDto>(order);

orderDto.CustomerName = "Joe";

Mapper.Map(orderDto, order);

order.Customer.Name.ShouldEqual("Joe");

Customizing reverse mapping

AutoMapper will automatically reverse map "Customer.Name" from "CustomerName" based on the original flattening. If you use MapFrom, AutoMapper will attempt to reverse the map:

cfg.CreateMap<Order, OrderDto>()
    .ForMember(d => d.Name, opt => opt.MapFrom(src => src.Customer.Name))
    .ReverseMap();

As long as the MapFrom path are member accessors, AutoMapper will unflatten from the same path (Name => Customer.Name).

If you need to customize this, for a reverse map you can use ForPath:

cfg.CreateMap<Order, OrderDto>()
    .ForMember(d => d.Name, opt => opt.MapFrom(src => src.Customer.Name))
    .ReverseMap()
    .ForPath(s => s.Customer.Details.Name, opt => opt.MapFrom(src => src.Name));

For most cases you shouldn't need this, as the original MapFrom will be reversed for you. Use ForPath when the path to get and set the values are different.