Facet.Extensions.EFCore 1.7.0

Facet

"One part of a subject, situation, object that has many parts."

Facet is a C# source generator that lets you define lightweight projections (DTOs, API models, etc.) directly from your domain models — without writing boilerplate.

It generates partial classes, records, structs, or record structs with constructors, optional LINQ projections, and even supports custom mappings — all at compile time, with zero runtime cost.

What is Facetting?

Facetting is the process of defining focused views of a larger model at compile time.

Instead of manually writing separate DTOs, mappers, and projections, Facet allows you to declare what you want to keep — and generates everything else.

You can think of it like carving out a specific facet of a gem:

• The part you care about
• Leaving the rest behind.

Why Facetting?

• Reduce duplication across DTOs, projections, and ViewModels
• Maintain strong typing with no runtime cost
• Stay DRY (Don't Repeat Yourself) without sacrificing performance
• Works seamlessly with LINQ providers like Entity Framework

Key Features

• ✅ Generate classes, records, structs, or record structs from existing types
• ✅ Exclude fields/properties you don't want (create a Facetted view of your model)
• ✅ Include public fields (optional)
• ✅ Auto-generate constructors for fast mapping
• ✅ LINQ projection expressions (Expression<Func<TSource,TTarget>>) -:white_check_mark: Custom mapping via IFacetMapConfiguration

Documentation

• Documentation & Guides
• What is being generated?

Quick Start

dotnet add package Facetusing Facet;

public class Person
{
    public string Name { get; set; }
    public string Email { get; set; }
    public int Age { get; set; }
}

// Generate a DTO that excludes Email
[Facet(typeof(Person), exclude: nameof(Person.Email))]
public partial class PersonDto { }

var person = new Person { Name = "Alice", Email = "a@b.com", Age = 30 };
var dto = new PersonDto(person); // Uses generated constructor

LINQ projection support:

var query = dbContext.People.Select(PersonDto.Projection).ToList();

Advanced Scenarios

• Generate records, structs, or record structs
• Include/exclude fields and properties
• Custom mapping logic for derived or formatted values
• Seamless integration with LINQ and EF Core

See the Advanced Scenarios guide for more.

Facet.Extensions for LINQ/EF Core async

Install Facet.Extensions for one-line mapping helpers:

dotnet add package Facet.Extensionsusing Facet.Extensions;

// Single object
var dto = person.ToFacet<Person, PersonDto>();

// Lists
var dtos = people.SelectFacets<Person, PersonDto>();

// IQueryable deferred projection
var query = dbContext.People.SelectFacet<Person, PersonDto>();

// EF Core async
var dtos = await dbContext.People.ToFacetsAsync<Person, PersonDto>();
var single = await dbContext.People.FirstFacetAsync<Person, PersonDto>();

Facet — Define less, project more.