Ignore destination member in AutoMapper not working

Question

I have the following simple classes and mappings that ignore Id field.
What I noticed is that the .Ignore() does not work when I'm mapping from Eto/Dto to Entity and I do not know the reason behind it.

I'm using the latest ABP 4.4.

public class Country : Entity<string>
{
    public Country() {}
    public Country(string id) { Id = id; }
}

public class CountryDto : EntityDto<string> { }

CreateMap<Country, CountryDto>().Ignore(x => x.Id); // id ignored
CreateMap<CountryDto, Country>().Ignore(x => x.Id); // id not ignored

Mapping code in my test:

var country1 = new Country("XX");
var dto1 = ObjectMapper.Map<Country, CountryDto>(country1);
        
var dto2 = new CountryDto() { Id = "XX" };
var country2 = ObjectMapper.Map<CountryDto, Country>(dto2);

I've also tried the normal AutoMapper long form to ignore instead of ABP's Ignore extension.

Answer 1

AutoMapper maps to destination constructors based on source members.

There are several ways to ignore id in destination constructors:

1. Map id constructor parameter to null.

   CreateMap<Country, CountryDto>().Ignore(x => x.Id);
// CreateMap<CountryDto, Country>().Ignore(x => x.Id);
   CreateMap<CountryDto, Country>().Ignore(x => x.Id).ForCtorParam("id", opt => opt.MapFrom(src => (string)null));

2. Specify ConstructUsing.

   CreateMap<Country, CountryDto>().Ignore(x => x.Id);
// CreateMap<CountryDto, Country>().Ignore(x => x.Id);
   CreateMap<CountryDto, Country>().Ignore(x => x.Id).ConstructUsing(src => new Country());

3. Rename id param in Country constructor.

// public Country(string id) { Id = id; }
   public Country(string countryId) { Id = countryId; }

4. DisableConstructorMapping for all maps.

DisableConstructorMapping(); // Add this
CreateMap<Country, CountryDto>().Ignore(x => x.Id);
CreateMap<CountryDto, Country>().Ignore(x => x.Id);

5. Exclude constructors with any parameter named id.

ShouldUseConstructor = ci => !ci.GetParameters().Any(p => p.Name == "id"); // Add this
CreateMap<Country, CountryDto>().Ignore(x => x.Id);
CreateMap<CountryDto, Country>().Ignore(x => x.Id);

Reference: https://docs.automapper.org/en/v10.1.1/Construction.html