DeltaMapper 1.2.0

DeltaMapper

Fast, diff-aware .NET object mapper. MIT licensed. Minimal dependencies.

Why DeltaMapper?

• Near-zero overhead — source-generated direct calls run at 7 ns, same as hand-written code
• MappingDiff<T> — map and get a structured change set in one call
• Source generator — [GenerateMap] emits assignment code at build time, zero reflection; [IgnoreMember], [MapMember], and [NullSubstitute] attributes customize maps without runtime Profiles
• Full IMapper pipeline — DI, middleware, hooks, EF Core proxy detection, OpenTelemetry tracing
• ProjectTo<T>() — translate profile maps into EF Core-compatible SQL projections via IQueryable

Install

dotnet add package DeltaMapper                    # core runtime
dotnet add package DeltaMapper.SourceGen          # optional: compile-time codegen
dotnet add package DeltaMapper.EFCore             # optional: EF Core proxy awareness + ProjectTo
dotnet add package DeltaMapper.OpenTelemetry      # optional: Activity spans

Requires .NET 8+ (binaries for net8.0, net9.0, and net10.0).

Quick Start

public class UserProfile : Profile
{
    public UserProfile()
    {
        CreateMap<User, UserDto>()
            .ForMember(d => d.FullName, o => o.MapFrom(s => $"{s.First} {s.Last}"))
            .ReverseMap();
    }
}

var mapper = MapperConfiguration.Create(cfg => cfg.AddProfile<UserProfile>())
    .CreateMapper();

var dto = mapper.Map<User, UserDto>(user);

Built-in Change Tracking

var diff = mapper.Patch(updateDto, existingUser);

if (diff.HasChanges)
    await auditLog.RecordAsync(userId, diff.Changes);

EF Core ProjectTo

Project directly from an IQueryable to a DTO — EF Core translates the mapping expression to SQL.

var config = MapperConfiguration.Create(cfg => cfg.AddProfile<OrderProfile>());

var dtos = await dbContext.Orders
    .Where(o => o.IsActive)
    .ProjectTo<Order, OrderDto>(config)
    .ToListAsync();

Flattening and Unflattening

Nested objects are flattened to flat DTOs and back automatically — no configuration required.

// Order.Customer.Name → CustomerName (flattening)
CreateMap<Order, OrderFlatDto>();

// CustomerName → Customer.Name (unflattening)
CreateMap<OrderFlatDto, Order>();

Assembly Scanning

// Register all profiles in an assembly in one call
cfg.AddProfilesFromAssemblyContaining<UserProfile>();

Type Converters

// Apply a conversion across every map that has a matching type pair
cfg.CreateTypeConverter<string, DateTime>(s => DateTime.Parse(s));

Conditional Mapping

// Skip mapping a property when a condition is not met
CreateMap<Order, OrderDto>()
    .ForMember(d => d.Discount, o => o.Condition(s => s.IsPremiumCustomer));

Source Generator Attributes

Customize compile-time maps with attributes on the partial profile class — no runtime Profile required.

[GenerateMap(typeof(User), typeof(UserDto))]
[IgnoreMember(typeof(User), typeof(UserDto), nameof(UserDto.InternalId))]
[MapMember(typeof(User), typeof(UserDto), nameof(UserDto.FullName), nameof(User.Name))]
[NullSubstitute(typeof(User), typeof(UserDto), nameof(UserDto.DisplayName), "Anonymous")]
public partial class UserMappingProfile { }

Requires DeltaMapper.SourceGen.

Performance

Getting Help

• GitHub Issues — bug reports and feature requests
• GitHub Discussions — questions

Links

• GitHub
• API Reference
• EF Core Integration
• Source Generator Guide
• Migration from AutoMapper
• Benchmarks