Dernière version du 4 mars 2025 à 15:17

Description

Permet le mapping d'un objet de type A vers un objet de type B.
AutoMapper utilise des convention de mapping afin de réduire le paramétrage:

Propriétés de même nom
Flattening
Ignore les références null

Liens

Getting Started
Static and Instance API
AutoMapper.Collection bibliothèque externe pour géré les collections
Map 1 object to list of objects

Setup and configuration

var config = new MapperConfiguration(cfg => {

    // configure mapping from Source to Dest
    cfg.CreateMap<Source, Dest>();

    // load the configuration from AppProfile
    cfg.AddProfile<AppProfile>();

    // load the configuration from all classes who inherits from Profile in the current assembly
    cfg.AddMaps(typeof(ContainerConfig).Assembly);
});

IMapper mapper = config.CreateMapper();
IMapper mapper = new Mapper(config);

Configuration

Profile

AProfile.cs

internal sealed class AProfile : Profile
{
    public AProfile()
    {
        CreateMap<A, B>()
            .ForMember(dest => dest.B1, opt => opt.MapFrom(src => src.A1));

        CreateMap<B, A>()
            .ForMember(dest => dest.A1, opt => opt.MapFrom(src => src.B1));
            .ForAllOtherMembers(opt => opt.Ignore()); // ignore all other members

        CreateMap<A, C[]>()
            .ConvertUsing<AToCsConverter>();
    }
}

public class AToCsConverter : ITypeConverter<A, C[]>
{
    public C[] Convert(A source, C[] destination, ResolutionContext context)
    {
        return new C[];
    }
}

Dependency Injection

Program.cs

appBuilder.Services.AddAutoMapper(typeof(Program));

Controllers/ItemController.cs

private readonly IMapper mapper;

public ItemController(IMapper mapper)
{
    this.mapper = mapper;
}

AutoMapper 12-

Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    // if all the profiles are in the current assembly
    services.AddAutoMapper(typeof(Startup));

    // add as parameter one type for each assembly
    services.AddAutoMapper(typeof(ProfileTypeFromAssembly1), typeof(ProfileTypeFromAssembly2));

Controllers/ItemController.cs

private readonly IMapper mapper;

public ItemController(ItemDbContext context, IMapper mapper)
{
    this.mapper = mapper;
}

WPF

App.xaml.cs

protected override void RegisterTypes(IContainerRegistry containerRegistry)
{
    var config = new MapperConfiguration(cfg =>
    {
        cfg.AddMaps(typeof(App).Assembly);
    });

    containerRegistry.RegisterSingleton<IMapper>(() => config.CreateMapper());
}

Exemple

var config = new MapperConfiguration(cfg =>
{
    cfg.CreateMap<A, B>()
        .ForMember(dst => dst.Q2, opts => opts.MapFrom(src => src.P2)); // map A.P2 → B.Q2
        .ReverseMap(); // map B → A
});
IMapper mapper = config.CreateMapper();

C c = new C() { P1 = 3 };
A a = new A() { P1 = 1, C1 = c };
B b = mapper.Map<B>(a);
// b.P1 = 1, b.Q2 = 2, b.C1P1 = 3

class A
{
    public int P1 { get; set; }
    public int P2 { get; set; }
    public C C1 { get; set; }
}

class B
{
    public int P1 { get; set; }    // mapping par convention avec A.P1
    public int Q2 { get; set; }    // mapping par configuration avec A.P2
    public int C1P1 { get; set; }  // mapping par flattening avec A.C1.P1
}

class C
{
    public int P1 { get; set; }
}

Flattening

Record

For records with a primary constructor, use ForCtorParam and fill all the constructor parameters.

CreateMap<A, B>()
    .ForCtorParam(nameof(B.P1), opt => opt.MapFrom(src => src.P1))
    .ForCtorParam(nameof(B.Q2), opt => opt.MapFrom(src => src.P2))
    .ForCtorParam(nameof(B.C1P1), opt => opt.MapFrom(src => src.C1.P1));
});

record A(int P1, int P2, C C1);
record B(int P1, int Q2, int C1P1);
record C(int P1);

Flattening

var config = new MapperConfiguration(cfg =>
{
    // default flattening
    // naming convention:    SpecificItem.Category   → SpecificItemDto.Category 
    // flatening conventing: SpecificItem.Item.Id    → SpecificItemDto.ItemId
    // configuration:        SpecificItem.Item.Code  → SpecificItemDto.Code
    cfg.CreateMap<SpecificItem, SpecificItemDto>()
       .ForMember(dest => dest.Code, opt => opt.MapFrom(src => src.Item.Code));

    // flattening from composition to inheritance
    // naming convention:    SpecificItem.Category   → SpecificItemDtoV2.Category
    // configuration: explicitly call the mapping of Item → SpecificItemDtoV2 for the Item property
    cfg.CreateMap<SpecificItem, SpecificItemDtoV2>()
       .IncludeMembers(x => x.Item);
    // naming convention: Item.Id   → ItemDtoV2.Id
    // naming convention: Item.Code → ItemDtoV2.Code
    cfg.CreateMap<Item, ItemDtoV2>();
    // MemberList.None to skip validation and ignore unmapped destination properties like Category
    cfg.CreateMap<Item, SpecificItemDtoV2>(MemberList.None)
       .IncludeBase<Item, ItemDtoV2>();
});

config.AssertConfigurationIsValid();
IMapper mapper = config.CreateMapper();

var specificItem = new SpecificItem
{
    Item = new Item
    {
        Id = 1,
        Code = 2
    },
    Category = 3
};

var specificItemDto = mapper.Map<SpecificItemDto>(specificItem);

var specificItemDtoV2 = mapper.Map<SpecificItemDtoV2>(specificItem);

// source
class Item
{
    public int Id { get; set; }
    public int Code { get; set; }
}

class SpecificItem
{
    public int Category { get; set; }
    public Item Item { get; set; }
}

// destination
class SpecificItemDto
{
    public int ItemId { get; set; }
    public int Code { get; set; }
    public int Category { get; set; }
}

class ItemDtoV2
{
    public int Id { get; set; }
    public int Code { get; set; }
}

class SpecificItemDtoV2 : ItemDtoV2
{
    public int Category { get; set; }
}

Unflattening

// unflattening UserDto.GroupId → User.Group.Id
this.CreateMap<UserDto, User>()
    .ForPath(dest => dest.Group.Id, opt => opt.MapFrom(src => src.GroupId));

List and polymorphism

// avec une liste
List<B> listB = Mapper.Map<List<A>, List<B>>(listA);

// polymorphism
cfg.CreateMap<Parent1, Parent2>()
    .Include<Child1, Child2>();
    // IncludeAllDerived(); to include all the derived classes
// without the include, the resulting list contains only Parent2 objects (no Child2 objects)

cfg.CreateMap<Child1, Child2>();

var lp1 = new List<Parent1> { new Parent1 { P1 = 1}, new Child1 { P1 = 2, P2 = 22 } };
var lp2 = mapper.Map<List<Parent2>>(lp1);
// Parent2, Child2

class Parent1
{
    public int P1 { get; set; }
}

class Child1 : Parent1
{
    public int P2 { get; set; }
}

class Parent2
{
    public int P1 { get; set; }
}

class Child2 : Parent2
{
    public int P2 { get; set; }
}

Mapping Inheritance

Pass parameter to the mapping

var config = new MapperConfiguration(cfg =>
{
    cfg.CreateMap<A, B>()
        .ForMember(dest => dest.P1,
            opt => opt.MapFrom((src, _, _, context) => src.P1 + (int)context.Items["+"]));
});

IMapper mapper = config.CreateMapper();

var a = new A { P1 = 1 };
var b = mapper.Map<B>(a, opt => opt.Items["+"] = 9);

Map 1 object to multiple objects

// map 1 Group to many User

class Group
{
    public int Id { get; set; }
    public ICollection<int> UserIds { get; } = new List<int>();
}

class User
{
    public int Id { get; set; }
    public int GroupId { get; set; }
}

Flatten to ValueType

var config = new MapperConfiguration(cfg =>
{
    cfg.CreateMap<(Group group, int userId), User>()
        .IncludeMembers(s => s.group)  // call the mapping Group → User
        .ForMember(dest => dest.Id, opt => opt.MapFrom(src => src.userId));

    cfg.CreateMap<Group, User>()
        .ForMember(dest => dest.GroupId, opt => opt.MapFrom(src => src.Id))
        .ForMember(dest => dest.Id, opt => opt.Ignore());
});

IMapper mapper = config.CreateMapper();

var group = new Group
{
    Id = 9,
    UserIds = {1, 2, 3}
};

IEnumerable<(int groupId, int userId)> groupAndUserList = group.UserIds.Select(x => ValueTuple.Create(group.Id, x));
var users = mapper.Map<IEnumerable<User>>(groupAndUserList).ToList();

Flatten with a ITypeConverter

var config = new MapperConfiguration(cfg =>
{
    cfg.CreateMap<int, User>()
        .ForMember(dest => dest.Id, opt => opt.MapFrom(src => src));

    cfg.CreateMap<Group, User>()
        .ForMember(dest => dest.GroupId, opt => opt.MapFrom(src => src.Id))
        .ForMember(dest => dest.Id, opt => opt.Ignore());

    cfg.CreateMap<Group, IEnumerable<User>>()
        .ConvertUsing<GroupToUsersConverter>();
});

IMapper mapper = config.CreateMapper();

var group = new Group
{
    Id = 9,
    UserIds = { 1, 2, 3 }
};
var users = mapper.Map<IEnumerable<User>>(group).ToList();

// use a converter to flatten a Group
class GroupToUsersConverter : ITypeConverter<Group, IEnumerable<User>>
{
    public IEnumerable<User> Convert(
        Group source,
        IEnumerable<User> destination,
        ResolutionContext context)
    {
        foreach (var userId in source.UserIds)
        {
            var user = context.Mapper.Map<User>(userId);
            context.Mapper.Map(source, user);

            yield return user;
        }
    }
}

Conditional mapping

cfg.CreateMap<A, B>()
   // map A.P2 → B.Q2 if A.P2 > 0
   // if A.P2 <= 0 → B.Q2 = 0
   .ForMember(dest => dest.Q2,
              opt =>
              {
                  opt.Condition(src => src.P2 > 0);
                  opt.MapFrom(src => src.P2);
              });

Before and After Map Action

cfg.CreateMap<A, B>()
   .BeforeMap((src, dest) => src.P1 += 1)
   .AfterMap((src, dest) => dest.P1 -= 1);

Inject a dependency during the mapping with a ValueResolver

Program.cs

// UserProvider is injected as a dependency, and AutoMapper has to be injected as a dependency too
appBuilder.Services.AddScoped<IUserProvider, UserProvider>()
                   .AddAutoMapper(typeof(AProfile));

AProfile.cs

public class AProfile : Profile
{
    public AProfile()
    {
        this.CreateMap<A, B>()
            .ForMember(x => x.User, opt => opt.MapFrom<UserValueResolver>());
    }
}

// UserProvider is retrieved as a dependency and used to resolve the mapping
public class UserValueResolver(IUserProvider userProvider) : IValueResolver<A, B, User>
{
    public User Resolve(A source, B destination, User member, ResolutionContext context)
    {
        return userProvider.GetUser();
    }
}

Errors

A lambda expression with a statement body cannot be converted to an expression tree

this.CreateMap<Class1, Class2>()
    .ForMember(dest => dest.Prop1, opt => opt.MapFrom(src =>
    {
        // ...
    }));

// use a new overload of MapFrom
this.CreateMap<Class1, Class2>()
    .ForMember(dest => dest.Prop1, opt => opt.MapFrom((src, dest) =>
    {
        // ...
    }));

MOQ

var mapperMock = new Mock<IMapper>();
mapperMock.Setup(x => x.Map<ItemDto>(It.IsAny<Item>()))
          .Returns(new ItemDto());

Unit tests

MyProfileTests.cs

public class MyProfileTests
{
    private readonly Fixture fixture;
    private readonly MapperConfiguration configuration;
    private readonly IMapper mapper;

    public MyProfileTests()
    {
        fixture = new();
        configuration = new MapperConfiguration(cfg => cfg.AddProfile<MyProfile>());
        mapper = configuration.CreateMapper();
    }

    [Fact]
    public void MyProfile_IsValid()
        => configuration.AssertConfigurationIsValid();

    [Fact]
    public void Map_SourceToDestination_ShouldMapCorrectly()
    {
        // Arrange
        var source = fixture.Create<MySource>();

        // Act
        var destination = mapper.Map<MyDestination>(source);

        // Assert
        Assert.NotNull(destination);
        Assert.Equal(source.Property1, destination.Property1);
    }

Dependency Injection

The ctor of MyValueResolver take a parameter of type IMyService.
So to test the profile, you have to inject IMyService to resolve MyValueResolver.

MyProfileTests.cs

public class MyProfileTests
{
    private readonly Fixture fixture;
    private readonly IMapper mapper;

    public MyProfileTests()
    {
        mockMyService = new Mock<IMyService>();
        mockApplicationUserProvider
            .Setup(x => x.GetData())
            .Returns(fixture.Create<Data>());

        var serviceProvider = new ServiceCollection()
            .AddSingleton(mockMyService.Object)
            .AddSingleton<MyValueResolver>()
            .AddAutoMapper(cfg => cfg.AddProfile<MyProfile>())
            .BuildServiceProvider();

        mapper = serviceProvider.GetRequiredService<IMapper>();
    }

Mock the mapper

// create a mock mapper
var mockMapper = new Mock<IMapper>();
// mock the mapping
this.mockMapper.Setup(x => x.Map<MyDto>(It.IsAny<MyEntity>()))
               .Returns(myDto);

// or create a new simplified mapper
var mapper = new Mapper(
    new MapperConfiguration(
        cfg =>
        {
            cfg.CreateMap<MyEntity, MyDto>()
               .ForMember(dest => dest.Property1, opt => opt.Ignore());
        }));

Installation

NuGet → AutoMapper

ASP.NET Core

NuGet → AutoMapper.Extensions.Microsoft.DependencyInjection

Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddAutoMapper(typeof(Startup));

MyController.cs

private readonly IMapper mapper;

public MyController(IMapper mapper)
{
    this.mapper = mapper;

    B b = this.mapper.Map<A, B>(a);

Configuration dans Profile