Najlot.Map.SourceGenerator 0.2.0

Najlot.Map

Najlot.Map is a high-performance object mapping library for .NET built around explicit mapping methods. Instead of convention-heavy auto-mapping, it keeps mapping logic in normal C# methods so behavior stays readable, predictable, and easy to review. When you want less boilerplate, you can add the optional source generator and keep the same programming model.

Najlot.Map is a good fit when you want:

• explicit mappings instead of hidden conventions,
• strong runtime performance without magic in the hot path,
• a single IMap entry point for object, collection, async, and queryable mapping,
• the option to scale from handwritten methods to generated mappings.

Why Najlot.Map

• Unlike convention-based mappers, mapping behavior lives in regular C# methods you can read, debug, and review directly.
• Unlike tools that rely on runtime magic, Najlot.Map keeps the hot path explicit and lets you add source generation only when it helps.
• Unlike broad auto-mapping defaults, it favors predictable registrations and validation so mapping changes are easier to catch in tests or startup checks.

What It Does

• Explicit method-based mappings
• Central IMap container
• Object, collection, nullable, and async enumerable mapping
• IQueryable<T> projections through expressions
• Optional Roslyn source generator
• Validation for delegate-based mappings in tests
• Factory-based object creation for DI or custom activation

Packages

Najlot.Map is distributed as two NuGet packages:

Installation

Install the runtime package:

dotnet add package Najlot.Map

Add the source generator when you want compile-time generated mappings:

dotnet add package Najlot.Map.SourceGenerator

Core Model

• Mappings are regular methods, not configuration files.
• IMap is the single entry point for registration and execution.
• Public mapping methods can be discovered and registered automatically.
• Generated mappings follow the same runtime API as handwritten mappings.
• Validation is meant for tests and startup checks, not the request path.

Quick Start

1. Write mapping methods

using Najlot.Map;
using Najlot.Map.Attributes;

internal class UserMappings
{
    [MapIgnoreProperty(nameof(User.Password))]
    public void MapModelToUser(IMap map, UserModel from, User to)
    {
        to.Id = from.Id;
        to.Username = from.Username;
        to.Features = map
            .From<UserFeatureModel>(from.Features)
            .ToList<UserFeature>();
    }

    [MapIgnoreProperty(nameof(UserModel.Password))]
    public UserModel MapUserToModel(IMap map, User from) => new()
    {
        Id = from.Id,
        Username = from.Username,
        Features = map
            .From<UserFeature>(from.Features)
            .To<UserFeatureModel>()
    };

    [MapIgnoreMethod]
    public Guid IgnoredMethod(UserModel from) => from.Id;
}

2. Register the mappings

var map = new Map()
    .Register<UserMappings>();

If your mapping classes need custom construction, register a factory:

var map = new Map()
    .RegisterFactory(type => serviceProvider.GetRequiredService(type))
    .Register<UserMappings>();

3. Map objects and collections

var user = map.From(userModel).To<User>();
var users = map.From(userModels).To<User>().ToList();

Registration Options

Manual registration

Register a class and let Najlot.Map inspect its public methods:

var map = new Map()
    .Register<UserMappings>();

Supported method shapes include:

void Map(TFrom from, TTo to)
void Map(IMap map, TFrom from, TTo to)
TTo Map(TFrom from)
TTo Map(IMap map, TFrom from)
Expression<Func<TFrom, TTo>> Projection()

Generated registration

When using Najlot.Map.SourceGenerator, classes marked with [Mapping] get picked up and the generator emits an assembly-specific extension method named Register{AssemblyName}Mappings().

var map = new Map()
    .RegisterMyProjectMappings();

If generated mapping classes need constructor injection, the same RegisterFactory(...) hook applies.

Source Generator

The source generator keeps the same explicit programming model while removing repetitive mapping code.

using Najlot.Map;
using Najlot.Map.Attributes;

[Mapping]
public partial class UserMappings
{
    public partial void MapUser(IMap map, UserModel from, User to);
    public partial void MapFeature(IMap map, UserFeatureModel from, UserFeature to);

    public DateTime ConvertToUtc(DateTimeOffset offset) => offset.UtcDateTime;
}

Usage:

var map = new Map()
    .RegisterMyProjectMappings();

var user = map.From(userModel).To<User>();

Use the generator when you want to reduce boilerplate but still keep mappings explicit, typed, and reviewable.

Validation

Validate() checks registered delegate-based mappings and throws MapMissPropertiesException when destination properties are left unmapped and not explicitly ignored.

var map = new Map()
    .Register<UserMappings>();

map.Validate();

Recommended usage:

• unit tests,
• integration tests,
• application startup checks.

Validation does not cover expression-based mappings used for IQueryable<T> projections.

Queryable Projections

For IQueryable<T> scenarios such as Entity Framework Core, register an expression mapping so the provider can translate it.

using System.Linq.Expressions;
using Najlot.Map.Attributes;

[Mapping]
public partial class UserMappings
{
    public static partial Expression<Func<User, UserListItem>> ToListItem();
}

Usage:

var map = new Map()
    .RegisterMyProjectMappings();

var query = map.From(db.Users).To<UserListItem>();
var items = await query.ToListAsync();

Use delegate mappings for in-memory object graphs. Use expression mappings when the projection needs to stay provider-translatable.

Design Principles

Najlot.Map is intentionally not a convention-over-configuration auto-mapper. Its value is in making mappings obvious and controllable while still giving you enough tooling to keep the codebase fast and maintainable as it grows.

That means:

• explicit code over implicit behavior,
• predictable runtime behavior over hidden fallback rules,
• optional generation over mandatory framework ceremony.

License

MIT License