AotObjectMapper

AotObjectMapper is a C# Roslyn source generator for compile-time object mapping.

This project was created primarily as a personal learning exercise and proof of concept. And may not be suitable for production use until v1.0.0

The main goals of this project are:

• Gaining hands-on experience with Roslyn incremental source generators
• Designing an AOT- and trimming-friendly alternative to reflection-based mappers
• Providing feature parity with mature mapping libraries such as AutoMapper or Mapster
• Exploring compile-time code generation, diagnostics, and analyzers
• Experimenting with API design and developer experience in attribute driven tooling
• Handling complex mapping scenarios such as recursion, reference preservation, enum strategies, and custom member mappings

Installation

AotObjectMapper is distributed as a NuGet package.

Via .NET CLI

dotnet add package AotObjectMapper.Mapper

Via Visual Studio

1. Right-click your project → Manage NuGet Packages

2. Search for AotObjectMapper

3. Install the latest version

Both methods will automatically add AotObjectMapper.Abstractions.

Quick Start

class User
{
    public required Guid           Id          { get; set; }
    public required string         FirstName   { get; set; }
    public          string?        MiddleName  { get; set; }
    public required string         LastName    { get; set; }
    public required DateTimeOffset DateOfBirth { get; set; }
    public required string         Secret      { get; set; }
}

public class UserDto
{
    public Guid     Id           { get; set; }
    public string   FirstName    { get; set; } = String.Empty;
    public string?  MiddleName   { get; set; }
    public string   LastName     { get; set; } = String.Empty;
    public int      DayOfBirth   { get; set; }
    public int      MonthOfBirth { get; set; }
    public int      YearOfBirth  { get; set; }
    public TimeOnly TimeOfBirth  { get; set; }
}

[GenerateMapper]
[Map<User, UserDto>]
public partial class UserMapper;

When the project is built, the mapper will generate a static Map method on UserMapper which will map Id, FirstName, MiddleName and LastName.

The remaining members cannot be mapped automatically because they differ in type and/or name, or do not exist on one of the classes. This can be fixed using mapper configuration which is all covered in the documentation.

Multiple Map attributes can be added to a single mapper class:

[GenerateMapper]
[Map<User, UserDto>, Map<UserDto, User>]
public partial class UserMapper;

Other Features

• Ignore Members

  • Skip specific members in a mapping using ignoredMembers on [Map].

• IConvertible Member Mapping

  • Automatically maps members implementing IConvertible with optional format providers.

• Mapper Context

  • Optional MapperContext tracks depth, reference reuse, and additional data
  • Supports nested mappings, reference preservation, and contextual operations

• Manual Member Mapping

  • Override mapping for specific members using [ForMember<TSource, TDestination>]. Supports MapperContext.

• Enum Mapping

  • Map by name (default)
  • Map by value (MappingOptions.MapEnumsByValue)
  • Throw exceptions for unmapped values (MappingOptions.ThrowExceptionOnUnmappedEnum)

• Nested Object Mapping

  • Use [UseMap<TMapper, TSource, TDestination>] to compose complex object graphs
  • Optionally consolidate multiple [Map] into a single mapper
  • Reference Preservation
    • Prevent infinite loops for circular references using MappingOptions.PreserveReferences.
    • Ensures the same source object is mapped once per operation.

• Pre/Post Mapping Hooks

  • Run logic before or after mapping with [PreMap<TSource, TDestination>] and [PostMap<TSource, TDestination>].

• Multiple Map Configurations

  • Multiple [Map] attributes per mapper
  • Separate mapper classes or single consolidated mapper for layered mapping

• Customizable and Extensible

  • Full control over conversions, member handling, and mapping behavior while maintaining compile-time safety.

For more information visit the Docs