Library.Mapping.Fody 8.2.6

Library.Mapping

What is Library.Mapping?

Library.Mapping is a high-performance, compile-time object mapper for .NET applications. It generates mapping code during your build, eliminating both the runtime reflection overhead and common type-safety pitfalls of traditional mappers.

Why Compile-time Mapping?

• Performance: Mapping logic is generated and inlined during compilation. No reflection or emitted code at runtime.
• Type Safety: Catches potential mapping errors during build instead of at runtime.
• IDE Support: Full access to code analysis, refactoring tools, and intellisense.
• Debuggability: Trace actual mapping logic in code, set breakpoints, and step through mappings.

Compile-time vs Runtime Mapping

.NET Benchmark Results

Benchmark code in /benchmarks/Mapping.Benchmark.

Installation

1. Install NuGet package:

Install-Package Library.Mapping.Fody

2. Add FodyWeavers.xml: In the root of your project, add or update:

<Weavers>
  <Library.Mapping/>
</Weavers>

3. Build project:

• The weaver will generate mapper implementations during build.

Code Samples: Modern DTO-Entity Mapping

Define DTO and Entity:

using Library.Mapping;

public class UserDto {
    [MapTo(typeof(UserEntity))]
    public int Id { get; set; }
    public string Name { get; set; }
}

public class UserEntity {
    [MapFrom(typeof(UserDto))]
    public int Id { get; set; }
    public string Name { get; set; }
}

Operator Injection

Both source and target can define implicit/explicit conversion operators, or use provided extension methods:

var entity = userDto.MapTo<UserEntity>(); // Extension method
UserEntity entity2 = userDto; // Operator overload (if injected by mapping)

Usage

After building, mapping methods and conversions are generated. Example usage:

var dto = new UserDto { Id = 1, Name = "Alice" };
UserEntity entity = dto; // Implicitly mapped
var dto2 = entity.MapTo<UserDto>(); // Back to DTO

• All mappings are validated at compile-time.
• Customization via mapping attributes available (see wiki).

Build & Integration Tips

• Confirm Fody packages are installed and correct FodyWeavers.xml exists.
• Clean & rebuild if generated code isn't appearing.
• Compatible with .NET Core, .NET Framework, and SDK-style projects.
• No runtime dependency except standard BCL.

Test & Benchmark

• See /benchmarks/Mapping.Benchmark project for reproducible performance data.
• CI runs mapping integration tests on PRs.

Authors

• Mehmet Yoldaş (mehmet-yoldas)

Acknowledgements

• Inspired by Fody community and .NET performance advocates.
• Thanks to users reporting issues and requesting features.