EggMapper vs AutoMapper

Why Switch from AutoMapper?

Feature Comparison

Performance Comparison

EggMapper consistently outperforms AutoMapper on every scenario. Measured with BenchmarkDotNet on .NET 10 (x64):

Why EggMapper is Faster

1. Inlined nested maps — AutoMapper calls a separate delegate for each nested object. EggMapper embeds the child mapping directly into the parent expression tree, eliminating delegate invocation overhead.

2. Inlined collection loops — MapList<S,D>() compiles the entire for loop and element mapping as a single expression tree. No enumerator allocation, no per-element delegate call.

3. Static generic caching — FastCache<TSource, TDestination> is a static generic class. The JIT bakes the cache field address directly into calling code. No dictionary lookup, no hash computation.

4. Context-free delegates — For common maps (flat, nested, flattening), EggMapper compiles Func<TSource, TDestination> with zero boxing. AutoMapper always passes through a ResolutionContext.

5. Zero allocations — No per-map allocations beyond the destination object itself. AutoMapper allocates ResolutionContext and intermediate collections.

Allocation Comparison

// BenchmarkDotNet results — Flat mapping, 10 properties
// Lower is better

|     Method |     Mean | Allocated |
|----------- |---------:|----------:|
|     Manual |   12 ns  |     104 B |  <-- hand-written code
|  EggMapper |   15 ns  |     104 B |  <-- matches manual
| AutoMapper |   35 ns  |     232 B |  <-- 128 B extra per map
|    Mapster |   20 ns  |     104 B |
|   Mapperly |   13 ns  |     104 B |  <-- source generator (compile-time)

Migration Guide (5 minutes)

Step 1: Swap the NuGet Package

- dotnet add package AutoMapper
- dotnet add package AutoMapper.Extensions.Microsoft.DependencyInjection
+ dotnet add package EggMapper

Step 2: Find and Replace Namespace

- using AutoMapper;
+ using EggMapper;

Step 3: Update DI Registration

- services.AddAutoMapper(typeof(MyProfile).Assembly);
+ services.AddEggMapper(typeof(MyProfile).Assembly);

Step 4: Update ProjectTo Calls

EggMapper's ProjectTo takes both source and destination type parameters:

- query.ProjectTo<ProductDto>(config);
+ query.ProjectTo<Product, ProductDto>(config);

Step 5: Run Tests

All your existing CreateMap, ForMember, Profile, and IMapper code works unchanged.

API Differences

Most of the API is identical. Here are the differences worth knowing:

Migration Examples

ForMember with MapFrom

using EggMapper;

// Identical in both libraries
cfg.CreateMap<Customer, CustomerDto>()
    .ForMember(d => d.FullName, o => o.MapFrom(s => $"{s.FirstName} {s.LastName}"))
    .ForMember(d => d.City, o => o.MapFrom(s => s.Address.City));

Ignore

// Identical in both libraries
cfg.CreateMap<User, UserDto>()
    .ForMember(d => d.PasswordHash, o => o.Ignore());

ReverseMap

// Identical in both libraries
cfg.CreateMap<Order, OrderDto>().ReverseMap();

Profile

// Identical in both libraries
public class OrderProfile : Profile
{
    public OrderProfile()
    {
        CreateMap<Order, OrderDto>();
        CreateMap<OrderLine, OrderLineDto>();
    }
}

Conditions

// Identical in both libraries
cfg.CreateMap<Product, ProductDto>()
    .ForMember(d => d.Price,
               o => o.Condition(s => s.Price > 0));

BeforeMap / AfterMap

// Identical in both libraries
cfg.CreateMap<Order, OrderDto>()
    .AfterMap((src, dst) => dst.MappedAt = DateTime.UtcNow);

MaxDepth (self-referencing types)

// Identical in both libraries
cfg.CreateMap<Category, CategoryDto>()
    .MaxDepth(3);

Common Migration Gotchas

• ProjectTo signature — AutoMapper uses ProjectTo<TDest>(config), EggMapper uses ProjectTo<TSrc, TDest>(config). This is the most common compile error after migration.
• DI method name — AddAutoMapper() becomes AddEggMapper(). The parameters are identical.
• No behavioral differences — ForMember, Ignore, Condition, ReverseMap, BeforeMap, AfterMap, MaxDepth, IncludeBase all behave identically.
• Same-type mapping — If you have CreateMap<T, T>() calls for cloning, you can remove them. EggMapper auto-compiles these on first use.

Ready to Migrate?

dotnet add package EggMapper

Quick Start Guide | API Reference | GitHub