Facette.Abstractions 1.0.2

<p align="center"> <img src="docs/facette.png" alt="Facette logo" width="200" /> </p>

A C# source generator that auto-generates DTO mapping code from [Facette]-annotated partial records — zero reflection, zero runtime dependencies.

This project is entirely vibe coded with Claude Code.

Features

• Compile-time mapping — FromSource(), ToSource(), and LINQ Projection generated via Roslyn
• Property control — Include/Exclude lists, [MapFrom] renaming, [FacetteIgnore]
• Nested objects & collections — auto-detected nested DTOs with List<T>, arrays, HashSet<T>, ImmutableArray<T>
• Flattening — convention-based (HomeAddressCity) and explicit dot-notation ([MapFrom("HomeAddress.City")])
• Value conversions — custom Convert/ConvertBack methods on [MapFrom]
• Enum conversion — auto-detect enum↔string/int mismatches
• Nullable mode — AllNullable for PATCH DTOs, AllRequired for strict contracts
• Copy attributes — forward data annotations from source to DTO
• CRUD presets — FacettePreset.Create (no Id, no projection) and FacettePreset.Read (no ToSource)
• Conditional mapping — [MapWhen] for runtime-toggled property inclusion
• Hooks — OnAfterFromSource, OnBeforeToSource, OnAfterToSource partial methods
• Inheritance — base/derived DTO hierarchies
• Multi-source mapping — [AdditionalSource] to combine multiple source types
• Expression mapping — MapExpression<TResult>() rewrites DTO predicates to source expressions
• EF Core integration — ProjectToFacette() and WhereFacette() extensions (no reflection)
• 13 compile-time diagnostics — FCT001–FCT013 catch configuration errors early

Quick start

dotnet add package Facette.Abstractions
dotnet add package Facette

Define your model and DTO:

public class Employee
{
    public int Id { get; set; }
    public string FirstName { get; set; } = "";
    public string LastName { get; set; } = "";
    public string Email { get; set; } = "";
    public decimal Salary { get; set; }
    public string SocialSecurityNumber { get; set; } = "";
}

[Facette(typeof(Employee), "SocialSecurityNumber")]
public partial record EmployeeDto;

Use the generated code:

// Source → DTO
var dto = EmployeeDto.FromSource(employee);

// DTO → Source
var entity = dto.ToSource();

// LINQ projection (translates to SQL with EF Core)
var dtos = dbContext.Employees
    .Select(EmployeeDto.Projection)
    .ToListAsync();

Packages

Documentation

Full documentation is available in the mdbook — run mdbook serve docs/ to browse locally.

Credits

Facette was heavily inspired by Facet and Mapperly.

License

See LICENSE for details.