OpenMapper 0.0.2

OpenMapper

A lightweight object-to-object mapping library for .NET 8 with convention-based property mapping and a simple, AutoMapper-inspired API.

Features

• Convention-Based Mapping: Automatically maps properties with matching names and compatible types
• Custom Member Mapping: Use ForMember to define custom mapping expressions for any property
• Profile Organization: Group related mappings into reusable Profile classes
• Dependency Injection Ready: First-class support for .NET DI container with multiple registration styles
• Simple API: Clean, intuitive interface inspired by AutoMapper
• Zero Configuration for Simple Cases: Just create a map and go
• Lightweight: Minimal dependencies and straightforward implementation
• Type-Safe: Full generic type support with compile-time type checking

Installation

Install via NuGet Package Manager:

dotnet add package OpenMapper

Or via Package Manager Console:

Install-Package OpenMapper

Quick Start

Basic Usage

using OpenMapper;
using OpenMapper.Configuration;
using OpenMapper.Core;

// Define your models
public class UserDto
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Email { get; set; }
}

public class UserViewModel
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Email { get; set; }
}

// Create a profile
public class UserProfile : Profile
{
    public UserProfile()
    {
        CreateMap<UserDto, UserViewModel>();
    }
}

// Configure and use the mapper
var config = new MapperConfiguration(cfg =>
{
    cfg.AddProfile<UserProfile>();
});

var mapper = config.CreateMapper();

var userDto = new UserDto
{
    Id = 1,
    Name = "John Doe",
    Email = "john@example.com"
};

var viewModel = mapper.Map<UserViewModel>(userDto);

Dependency Injection Integration

OpenMapper provides three convenient ways to register with the .NET DI container:

Option 1: Pass Profile Types Directly

using OpenMapper.Extensions;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddOpenMapper(typeof(UserProfile), typeof(OrderProfile));

Option 2: Auto-Scan Assemblies

using OpenMapper.Extensions;

var builder = WebApplication.CreateBuilder(args);

// Scan the executing assembly for all Profile classes
builder.Services.AddOpenMapper(Assembly.GetExecutingAssembly());

Option 3: Fluent Configuration

using OpenMapper.Extensions;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddOpenMapper(cfg =>
{
    cfg.AddProfile<UserProfile>();
    cfg.AddProfile<OrderProfile>();
});

Then inject IMapper into your services:

public class UserService
{
    private readonly IMapper _mapper;

    public UserService(IMapper mapper)
    {
        _mapper = mapper;
    }

    public UserViewModel GetUser(int id)
    {
        var userDto = GetUserFromDatabase(id);
        return _mapper.Map<UserViewModel>(userDto);
    }
}

Detailed Usage

Creating Profiles

Profiles help organize related mappings:

public class MappingProfile : Profile
{
    public MappingProfile()
    {
        // Map from source to destination
        CreateMap<Customer, CustomerDto>();
        CreateMap<Order, OrderDto>();
        CreateMap<Product, ProductDto>();

        // Create reverse mappings if needed
        CreateMap<CustomerDto, Customer>();
        CreateMap<OrderDto, Order>();
    }
}

Mapping Methods

OpenMapper provides three mapping methods through the IMapper interface:

1. Generic Mapping (Recommended)

var destination = mapper.Map<TDestination>(source);

// Example
var viewModel = mapper.Map<UserViewModel>(userDto);

2. Non-Generic Mapping

object destination = mapper.Map(source, sourceType, destinationType);

// Example
var viewModel = mapper.Map(userDto, typeof(UserDto), typeof(UserViewModel));

3. Map to Existing Instance

mapper.Map(source, existingDestination);

// Example - useful for updating existing objects
var existingUser = new UserViewModel { Id = 1, Name = "Old Name" };
mapper.Map(userDto, existingUser);
// existingUser is now updated with values from userDto

Convention-Based Mapping Rules

OpenMapper automatically maps properties when:

1. Names match: Source and destination properties have the same name (case-sensitive)
2. Types are compatible: Destination type is assignable from source type

public class Source
{
    public int Id { get; set; }           // ✓ Maps to Id
    public string Name { get; set; }      // ✓ Maps to Name
    public DateTime Created { get; set; } // ✓ Maps to Created
    public int Age { get; set; }          // ✗ No matching property in destination
}

public class Destination
{
    public int Id { get; set; }
    public string Name { get; set; }
    public DateTime Created { get; set; }
    public string Email { get; set; }     // ✗ No matching property in source (will be default)
}

Custom Member Mapping with ForMember

Use ForMember to customize how individual properties are mapped. This is useful when:

• Property names don't match
• You need to transform or calculate values
• You need to map from nested properties
• Types need conversion

public class Book
{
    public string Title { get; set; }
    public List<string> Chapters { get; set; }
    public decimal Price { get; set; }
    public int Stock { get; set; }
}

public class BookDto
{
    public string Title { get; set; }
    public int ChapterCount { get; set; }
    public string PriceDisplay { get; set; }
    public bool Available { get; set; }
}

public class BookProfile : Profile
{
    public BookProfile()
    {
        CreateMap<Book, BookDto>()
            // Map from a collection count
            .ForMember(dest => dest.ChapterCount,
                opt => opt.MapFrom(src => src.Chapters.Count))

            // Format a value with custom logic
            .ForMember(dest => dest.PriceDisplay,
                opt => opt.MapFrom(src => $"${src.Price:F2}"))

            // Map with a boolean expression
            .ForMember(dest => dest.Available,
                opt => opt.MapFrom(src => src.Stock > 0));

        // Title is auto-mapped by convention
    }
}

Complex Expressions

ForMember supports any valid C# expression:

public class UserDto
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public Address Address { get; set; }
    public List<Order> Orders { get; set; }
}

public class UserViewModel
{
    public string FullName { get; set; }
    public string City { get; set; }
    public int OrderCount { get; set; }
    public decimal TotalSpent { get; set; }
}

public class UserProfile : Profile
{
    public UserProfile()
    {
        CreateMap<UserDto, UserViewModel>()
            // String concatenation
            .ForMember(dest => dest.FullName,
                opt => opt.MapFrom(src => $"{src.FirstName} {src.LastName}"))

            // Nested property access
            .ForMember(dest => dest.City,
                opt => opt.MapFrom(src => src.Address.City))

            // LINQ expressions
            .ForMember(dest => dest.OrderCount,
                opt => opt.MapFrom(src => src.Orders.Count))

            .ForMember(dest => dest.TotalSpent,
                opt => opt.MapFrom(src => src.Orders.Sum(o => o.Total)));
    }
}

Type Conversion

ForMember automatically converts between compatible types:

public class Product
{
    public int Id { get; set; }
    public decimal Price { get; set; }
}

public class ProductDto
{
    public string Id { get; set; }        // int → string conversion
    public string Price { get; set; }     // decimal → string conversion
}

public class ProductProfile : Profile
{
    public ProductProfile()
    {
        CreateMap<Product, ProductDto>()
            .ForMember(dest => dest.Id,
                opt => opt.MapFrom(src => src.Id))        // Converts int to string

            .ForMember(dest => dest.Price,
                opt => opt.MapFrom(src => src.Price));    // Converts decimal to string
    }
}

Handling Null Values

When mapping from properties that might be null, handle nulls in your expression:

public class PersonDto
{
    public Address Address { get; set; }  // Might be null
}

public class PersonViewModel
{
    public string City { get; set; }
}

public class PersonProfile : Profile
{
    public PersonProfile()
    {
        CreateMap<PersonDto, PersonViewModel>()
            // Safe navigation with null-conditional operator
            .ForMember(dest => dest.City,
                opt => opt.MapFrom(src => src.Address?.City ?? "Unknown"))

            // Or use null-coalescing
            .ForMember(dest => dest.City,
                opt => opt.MapFrom(src => src.Address != null ? src.Address.City : "N/A"));
    }
}

Working with Complex Scenarios

Mapping Collections

var users = new List<UserDto>
{
    new UserDto { Id = 1, Name = "John" },
    new UserDto { Id = 2, Name = "Jane" }
};

var viewModels = users.Select(u => mapper.Map<UserViewModel>(u)).ToList();

Nested Objects

public class OrderDto
{
    public int Id { get; set; }
    public CustomerDto Customer { get; set; }
    public List<OrderItemDto> Items { get; set; }
}

public class OrderViewModel
{
    public int Id { get; set; }
    public CustomerViewModel Customer { get; set; }
    public List<OrderItemViewModel> Items { get; set; }
}

// Create mappings for all types
public class OrderProfile : Profile
{
    public OrderProfile()
    {
        CreateMap<OrderDto, OrderViewModel>();
        CreateMap<CustomerDto, CustomerViewModel>();
        CreateMap<OrderItemDto, OrderItemViewModel>();
    }
}

// Map the entire object graph
var orderViewModel = mapper.Map<OrderViewModel>(orderDto);
// Note: Nested objects are NOT automatically mapped - you need to map them separately

API Reference

MapperConfiguration

Entry point for configuring mappings.

public MapperConfiguration(Action<MapperConfiguration> configure)
public void AddProfile<TProfile>() where TProfile : Profile, new()
public void AddProfile(Profile profile)
public IMapper CreateMapper()

Profile

Base class for organizing mappings.

public abstract class Profile
{
    protected IMappingExpression<TSource, TDestination> CreateMap<TSource, TDestination>();
}

IMappingExpression<TSource, TDestination>

Fluent interface for configuring type mappings.

public interface IMappingExpression<TSource, TDestination>
{
    IMappingExpression<TSource, TDestination> ForMember<TMember>(
        Expression<Func<TDestination, TMember>> destinationMember,
        Action<MemberConfigurationExpression<TSource, TDestination, TMember>> memberOptions);
}

MemberConfigurationExpression<TSource, TDestination, TMember>

Configures custom mapping for a specific member.

public class MemberConfigurationExpression<TSource, TDestination, TMember>
{
    public void MapFrom<TSourceMember>(Expression<Func<TSource, TSourceMember>> sourceMember);
}

IMapper

Main interface for performing mappings.

public interface IMapper
{
    TDestination Map<TDestination>(object source);
    object Map(object source, Type sourceType, Type destinationType);
    void Map(object source, object destination);
}

Requirements

• .NET 8.0 or later
• Microsoft.Extensions.DependencyInjection.Abstractions 8.0.0 (automatically installed)

Limitations

Current version limitations (future enhancements planned):

• No value converters or type converters (basic type conversion supported via ForMember)
• No conditional mapping
• No before/after map actions
• No Ignore() support for explicitly ignoring properties
• Destination types must have parameterless constructors
• No automatic nested object mapping (you must map nested objects explicitly or use ForMember)

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

Building from Source

# Clone the repository
git clone https://github.com/chrisedg87/OpenMapper.git
cd OpenMapper

# Build the project
dotnet build OpenMapper.sln

# Run tests
dotnet test OpenMapper.Tests/OpenMapper.Tests.csproj

# Create NuGet package
dotnet pack OpenMapper.csproj -c Release

License

This project is licensed under the MIT License - see the LICENSE file for details.

Acknowledgments

Inspired by AutoMapper, OpenMapper provides a simpler, more lightweight alternative for projects that need basic object mapping functionality without the complexity of larger frameworks.

Support

• Report issues: GitHub Issues
• NuGet Package: OpenMapper