SourceMapper

Introduction

SourceMapper is a code generator that uses attributes placed in interfaces or abstract classes: during build time it generates mapping classes and methods for mappings based on "rules" defined in these attributes.

It is based on Source Generators feature that has been intoduced with C# 9.0 and brings a possibility to generate code during build time.

👉 After configuring you mappers you can see, control and override the generated code for the mappings. 👈

Installation

Install using nuget package manager:

Install-Package Compentio.SourceMapper

or .NET CLI:

dotnet add package Compentio.SourceMapper

How to use

To define mapping we have to mark mapping abstract class or interface with MapperAttribute:

[Mapper]
public interface INotesMapper
{
    NoteDto MapToDto(NoteDao source);
}

This will generate mapping class with default class name NotesMapper for properties that names are the same for NoteDto and NoteDao classes. The generated class is in the same namespace as its base abstract class of interface. It can be found in project in Visual Studio:

Dependencies -> Analyzers -> Compentio.SourceMapper.Generators.MainSourceGenerator.

When the names are different than we can use Source and Target names of the properties:

[Mapper(ClassName = "InterfaceUserMapper")]
public interface IUserMapper
{
    [Mapping(Source = nameof(UserDao.FirstName), Target = nameof(UserInfo.Name))]
    UserInfo MapToDomainMoodel(UserDao userDao);       
}

The ClassName property in MapperAttribute is responsible for name of the generated mapping class. For default MapperAttribute interface prefix I is removed or Impl suffix added to the generated class name if there is no I prefix in the mapping interface name.

Interface mapping

Use interfaces to prepare basic mapping. In a case when mapped object contains another objects, e.g.:

public class NoteDto
{
    public long Id { get; set; }
    public string Title { get; set; }
    public string Description { get; set; }
    public NoteDocumentDto Document { get; set; }
}

and

public class NoteDao
{
    public long Id { get; set; }
    public string PageTitle { get; set; }
    public string Description { get; set; }
    public NoteDocumentDao Document { get; set; }
}

it is enough to add mapping method to the interface for these types and the code generation processor will match and generate mappings for NoteDto MapToDto(NoteDao source) method:

[Mapper]
public interface INotesMapper
{
    [Mapping(Source = nameof(NoteDao.PageTitle), Target = nameof(NoteDto.Title))]
    NoteDto MapToDto(NoteDao source);

    [Mapping(Source = nameof(NoteDocumentDao.Metadata.CreatorFirstName), Target = nameof(NoteDocumentDto.Autor))]
    NoteDocumentDto MapToDto(NoteDocumentDao source);
}

the output will be:

public class NotesMapper : INotesMapper
{
    public static NotesMapper Create() => new();
    public virtual Compentio.Example.App.Entities.NoteDto MapToDto(Compentio.Example.App.Entities.NoteDao source)
    {
        if (source == null)
            return source;
        var target = new Compentio.Example.App.Entities.NoteDto();
        target.Id = source.Id;
        target.Title = source.PageTitle;
        target.Description = source.Description;
        target.Document = MapDocumentToDto(source.Document);
        return target;
    }

    public virtual Compentio.Example.App.Entities.NoteDocumentDto MapDocumentToDto(Compentio.Example.App.Entities.NoteDocumentDao source)
    {
        if (source == null)
            return source;
        var target = new Compentio.Example.App.Entities.NoteDocumentDto();
        target.Id = source.Id;
        target.Title = source.Title;
        return target;
    }
}

All methds are marked as virtual, so there is a possibility to override them in own mappers code.

Class mapping

For more complicated mapings use abstract class to define mappers. The main difference between abstract class mapper and interface, that Expression property can be used in MappingAttribute:

[Mapper(ClassName = "NotesMappings")]
public abstract class NotesClassMapper
{
    [Mapping(Target = nameof(NoteDocumentDto.Autor), Expression = nameof(ConvertAuthor))]
    public abstract NoteDocumentDto MapToDto(NoteDocumentDao source);

    protected readonly Func<NoteDocumentDao, string> ConvertAuthor = s => s.Metadata.CreatorFirstName + s.Metadata.CreatorLastName;
}

Expression - it is a name of mapping function, that can be used for additional properties mapping.

It must be public or protected, since it is used in generated mapper class that implements abstract mapping class.

Ignore mapping

If for any reason part of the class/interface properties should not be mapped, IgnoreMapping attribute should be used for that. Added IgnoreMapping causes that both source and target property during mapping generation will be omitted, not generating any linked map and not reporting any warning in diagnostics. If we have two classes NoteDao and NoteDto

public class NoteDao
{
	public long Id { get; set; }
	public string PageTitle { get; set; }
	public string Description { get; set; }

	[IgnoreMapping]
	public DateTime ValidFrom { get; set; }

	[IgnoreMapping]
	public DateTime ValidTo { get; set; }

	[IgnoreMapping]
	public string CreatedBy { get; set; }

	[IgnoreMapping]
	public DateTime Created { get; set; }

	[IgnoreMapping]
	public DateTime Modified { get; set; }
}

public class NoteDto
{
	public long Id { get; set; }
	public string Title { get; set; }
	public string Description { get; set; }
}

and we need to map only matched fields, the mapper class NotesClassMapper lead to creating proper mapping result class NotesMappings without any warning:

[Mapper(ClassName = "NotesMappings")]
public abstract partial class NotesClassMapper
{
	[Mapping(Source = nameof(NoteDao.PageTitle), Target = nameof(NoteDto.Title))]
	public abstract NoteDto MapToDto(NoteDao source);
}

public class NotesMappings : NotesClassMapper
{
	public override Compentio.Example.DotNetCore.App.Entities.NoteDto MapToDto(Compentio.Example.DotNetCore.App.Entities.NoteDao source)
	{
		if (source == null)
			return null;
		var target = new Compentio.Example.DotNetCore.App.Entities.NoteDto();
		target.Id = source.Id;
		target.Title = source.PageTitle;
		target.Description = source.Description;
		return target;
	}
}

Mapping collections

Lets assume we need to map two entities:

public class UserDao
{
    public long UserId { get; set; }
    public AddressDao[] UserAddresses { get; set; }
}

to

public class UserInfo
{
    public int Id { get; set; }
    public Address[] Addresses { get; set; }
}

It can be achieved using abstract class mapper:

[Mapper(ClassName = "UserDataMapper")]
public abstract class UserMapper
{
    [Mapping(Source = nameof(UserDao.UserAddresses), Target = nameof(UserInfo.Addresses), Expression = nameof(ConvertAddresses))]
    [Mapping(Source = nameof(UserDao.UserId), Target = nameof(UserInfo.Id), Expression = nameof(ConvertUserId))]
    public abstract UserInfoWithArray MapToDomainModel(UserWithArrayDao userWithArrayDao);

    protected Address[] ConvertAddresses(AddressDao[] addresses)
    {
        return addresses.Select(a => MapAddress(a)).ToArray();
    }
    
    protected static int ConvertUserId(long id)
    {
        return Convert.ToInt32(id);
    }

    public abstract Address MapAddress(AddressDao addressDao);
}

For more examples see Wiki examples.

Dependency injection

The Compentio.SourceMapper searches for 3 main dependency container packages (Microsoft.Extensions.DependencyInjection, Autofac.Extensions.DependencyInjection, and StructureMap.Microsoft.DependencyInjection) and generates extension code. If there no any container packages found, Dependency Injection extension class is not generated.

To simplify adding dependency injection for mappers MappersDependencyInjectionExtensions class is generated, that can be used by adding AddMappers() that adds all mappers defined in the project.

For Microsoft.Extensions.DependencyInjection, in service configuration:

 Host.CreateDefaultBuilder(args)
                .ConfigureServices((_, services) =>
                    services
                    //.here you services
                    //
                    .AddMappers());

In case of Autofac.Extensions.DependencyInjection, container configuration can be separated in module file AutofacModules, where we place registrations directly with Autofac:

public class AutofacModule : Module
{
	protected override void Load(ContainerBuilder builder)
	{
		// other services
		builder.AddMappers();
	}
}

That module need to be register in container configure section of Startup file:

public void ConfigureContainer(ContainerBuilder builder)
{
	builder.RegisterModule(new AutofacModule());
}

To run Autofac mechanism, we need to call Autofac factory with attached Startup file by using:

Host.CreateDefaultBuilder(args)
	.UseServiceProviderFactory(new AutofacServiceProviderFactory())
	.ConfigureWebHostDefaults(webBuilder =>
	{
		webBuilder.UseStartup<Startup>();
	});

For StructureMap, we add AddMappers in container configuration in Startup file:

public void ConfigureContainer(Container builder)
{
	builder.Configure(config =>
	{
		// other services
		config.AddMappers();
	});
}

In example project StructureMap container is builded by running StructureMapContainerBuilderFactory from program host

Host.CreateDefaultBuilder(args)
	.UseServiceProviderFactory(new StructureMapContainerBuilderFactory())
	.ConfigureWebHostDefaults(webBuilder =>
	{
		webBuilder.UseStartup<Startup>();
	});

where provider is a service provider factory class constructed for StructureMap mechanism (working with Container, not with Registry):

public class StructureMapContainerBuilderFactory : IServiceProviderFactory<Container>
{
	private IServiceCollection _services;

	public Container CreateBuilder(IServiceCollection services)
	{
		_services = services;
		return new Container();
	}

	public IServiceProvider CreateServiceProvider(Container builder)
	{
		builder.Configure(config =>
		{
			config.Populate(_services);
		});

		return builder.GetInstance<IServiceProvider>();
	}
}

Ninject Dependency Injection

SourceMapper allow also, in limited way, to use Ninject dependency injection. Solution is compatible with Ninject in version < 4 and work with Asp.Net Core projects. Integration with Ninject dependency injection is allowed by adding to project Ninject.Web.AspNetCore package. Ninject based on IKernel, so the SourceMapper generate mappers, which can be added by using AddMappers() method in Kernel declaration place in project. In our example, we created 'NinjectKernel' class with CreateKernel methods - it is place, where SourceMapper inject MapperDependencyInjectionExtension class, with all mappings generated from declared mappers.

/// Ninject Dependency Injection mechanism : kernel
public class NinjectKernel
{
	/// Method create kernel with all user defined dependency injections
	public static IKernel CreateKernel()
	{
		var settings = new NinjectSettings();
		settings.LoadExtensions = false;

		var kernel = new AspNetCoreKernel(settings);

		kernel.Load(typeof(AspNetCoreHostConfiguration).Assembly);
		// User Dependency Injections
		kernel.Bind<IInvoiceService>().To<InvoiceService>().InSingletonScope();
		kernel.Bind<IInvoiceRepository>().To<InvoiceRepository>().InSingletonScope();
		// Using mappers from SourceMapper
		kernel.AddMappers();

		return kernel;
	}
}

Next, CreateKernel is used in Program starting class, in host generating section:

var host = new NinjectSelfHostBootstrapper(NinjectKernel.CreateKernel, hostConfiguration);
host.Start();

Inverse Mapping Mechanism

Inverse mapping allow to create about half of the mapper code by automate. The main goal is to define only one way mapping methods in mapper class, the second one - inverse mapping - can be created by internal mechanism. Due to using dependency injections, SourceMapper generate additional part of mapping class (or interface), so the source mapping class (interface) must be declared as partial.

Interface Inverse Mapping

Inverse mapping is provided by using inverse mapping attributes, where the name of the inverse method is required, like in example (Compentio.Example.Autofac.App):

[Mapper]
public partial interface IBooksMapper
{
	[InverseMapping(InverseMethodName = "MapBookToDao")]
	BookDto MapBookToDto(BookDao source);
}

that lead to two methods implementations in mapper result class:

public class BooksMapper : IBooksMapper
{
        public static BooksMapper Create() => new();
        public virtual Compentio.Example.Autofac.App.Entities.BookDto MapBookToDto(Compentio.Example.Autofac.App.Entities.BookDao source)
        {
	...
        }

        public virtual Compentio.Example.Autofac.App.Entities.BookDao MapBookToDao(Compentio.Example.Autofac.App.Entities.BookDto source)
        {
	...
        }
}

If mapped object contain collections or other complex fields/expressions, mappings cant be created by automate. In this case we can create class that inherit mapper result class and override complex objects, for example:

public class CustomBooksMapper : BooksMapper
{
	public override BookDao MapBookToDao(BookDto source)
	{
	    var result = base.MapBookToDao(source);
	    result.LibraryAddressesDao = source.LibraryAddressesDto.Select(a => MapAddressToDao(a)).ToList();
	    return result;
	}
	...
}

and register it in dependency injection section

public class AutofacModule : Module
{
	protected override void Load(ContainerBuilder builder)
	{
	    ...
	    builder.AddMappers();
	    // Override mapper class by custom implementation
	    builder.RegisterType<CustomBooksMapper>().As<IBooksMapper>().SingleInstance();
	}
}

Class Inverse Mapping

Case of class inverse mapping is mainly similar to interfaces inverse mechanism. First of all, we need to mark class as partial and add inverse attribute with the name for inverse method. If mapping between classes need expresions, they both - primary and invers expression methods - should be implemented by developer. Inverse mechanism is not able to generate it by automate. On the Compentio.Example.AtructureMap.App example:

[Mapper(ClassName = "ClassInvoiceMapper")]
public abstract partial class InvoiceMapper
{
	...
	[InverseMapping(InverseMethodName = "MapInvoiceToDao")]
	public abstract InvoiceDto MapInvoiceToDto(InvoiceDao source);
	...
	[InverseMapping(InverseMethodName = "MapInvoiceItemToDao")]
        public abstract InvoiceItemDto MapInvoiceItemToDto(InvoiceItemDao source);
	
	protected IEnumerable<InvoiceItemDto> ConvertToItemsDto(IEnumerable<InvoiceItemDao> items)
	{
	    return items.Select(i => MapInvoiceItemToDto(i)).AsEnumerable();
	}
}

That prepared mapping class lead to obtained proper result mapping class:

public class ClassInvoiceMapper : InvoiceMapper
{
	public override Compentio.Example.StructureMap.App.Entities.InvoiceDto MapInvoiceToDto(Compentio.Example.StructureMap.App.Entities.InvoiceDao source)
	{
	    ...
	    target.Items = ConvertToItemsDto(source.Items);
	}

	public override Compentio.Example.StructureMap.App.Entities.InvoiceDao MapInvoiceToDao(Compentio.Example.StructureMap.App.Entities.InvoiceDto source)
	{
	    ...
	}

	public override Compentio.Example.StructureMap.App.Entities.InvoiceItemDto MapInvoiceItemToDto(Compentio.Example.StructureMap.App.Entities.InvoiceItemDao source)
	{
	...
	}

	public override Compentio.Example.StructureMap.App.Entities.InvoiceItemDao MapInvoiceItemToDao(Compentio.Example.StructureMap.App.Entities.InvoiceItemDto source)
	{
	...
	}
}

public abstract partial class InvoiceMapper
{
	public abstract Compentio.Example.StructureMap.App.Entities.InvoiceDao MapInvoiceToDao(Compentio.Example.StructureMap.App.Entities.InvoiceDto source);
	public abstract Compentio.Example.StructureMap.App.Entities.InvoiceItemDao MapInvoiceItemToDao(Compentio.Example.StructureMap.App.Entities.InvoiceItemDto source);
}

Now ClassInvoiceMapper can be inherited by, for example, CustomClassInvoiceMapper and complex methods can be overrided, similarly to interface case.