Automapper not mapping null value

Question

I'm trying to map a nullable property, but the automapper indicates an error in this mapping.

Property: HomeTown Source: Person.NaturalPerson.HomeTown

Destination: PersonDTO.NaturalPersonDTO.HomeTown

When the property is null in the source, the following error occurs:

Mapping types:
Person -> PersonDTO
LogSistemas.Domynus.Application.Core.Entities.Person.Person -> LogSistemas.Domynus.Application.Core.Dto.Person.PersonDTO

Type Map configuration:
Person -> PersonDTO
LogSistemas.Domynus.Application.Core.Entities.Person.Person -> LogSistemas.Domynus.Application.Core.Dto.Person.PersonDTO

Destination Member:
NaturalPerson

 ---> AutoMapper.AutoMapperMappingException: Error mapping types.

Mapping types:
NaturalPerson -> NaturalPersonDTO
LogSistemas.Domynus.Application.Core.Entities.Person.NaturalPerson -> LogSistemas.Domynus.Application.Core.Dto.Person.NaturalPersonDTO

Type Map configuration:
NaturalPerson -> NaturalPersonDTO
LogSistemas.Domynus.Application.Core.Entities.Person.NaturalPerson -> LogSistemas.Domynus.Application.Core.Dto.Person.NaturalPersonDTO

Destination Member:
HomeTown

 ---> System.NullReferenceException: Object reference not set to an instance of an object.

Classes

public class NaturalPerson
{
    public NaturalPerson()
    {
        HomeTown = new();
    }

    public City HomeTown { get; set; }
}

public class NaturalPersonDTO
{
    public NaturalPersonDTO()
    {
        HomeTown = new CityDTO();
    }

    public CityDTO HomeTown { get; set; }
}

Mapping config

    CreateMap<Entities.Person.Person, PersonDTO>();
    CreateMap<Entities.Person.NaturalPerson, NaturalPersonDTO>();
    CreateMap<City, CityDTO>()
        .ConvertUsing(x => new CityDTO
        {
            Id = x.Id,
            StateId = x.StateId,
            Name = x.Name,
            State = x.State.Abbreviation,
            Country = x.State.Country.Name
        });

As far as I know, automapper maps null without any problems. I couldn't figure this out.

The error complains about HomeTown, a CityDTO. You don't check whether x.State is null so x.State.Abbreviation will throw. Post the actual full exception text. You could avoid the error if you used x.State?.Abbreviation — Panagiotis Kanavos
– Panagiotis Kanavos, Commented Oct 25, 2024 at 14:39
That's just manual mapping. AM does the null checks for you, but you need to write a proper map, not a type converter. — Lucian Bargaoanu
– Lucian Bargaoanu, Commented Oct 25, 2024 at 15:19
Automapper try to map city of Hometown in NaturalPerson to DTO even if HomeTown is null? Exception complete text is too long for post here — Fernando Cristan
– Fernando Cristan, Commented Oct 25, 2024 at 15:22

Jivopis · Accepted Answer · 2024-10-25 14:49:57Z

2

You can't map your nullable property because your mapper profile specifically says to create new object CityDTO from City. So when City is null, then mapper can't perform what you told him.

You need to modify your mapping profile to something like this:

...
CreateMap<Entities.Person.NaturalPerson, NaturalPersonDTO>();
CreateMap<City, CityDTO>()
    .ForPath(dist => dist.State, op => op.MapFrom(src => src.State.Abbreviation))
    .ForPath(dist => dist.Country, op => op.MapFrom(src => src.State.Country.Name));

answered Oct 25, 2024 at 14:49

Jivopis

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3 Comments

Fernando Cristan Over a year ago

Automapper try to map city of Hometown in NaturalPerson to DTO even if HomeTown is null?

Jivopis Over a year ago

In your provided option you're making mandatory to create new CityDTO.

Fernando Cristan Over a year ago

ok, i get it, thansk for helping!!

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