🧠 AutoMapper vs Manual vs Mapster — Real-World Mapping in .NET

This Gist explores three mapping strategies in .NET: AutoMapper, Manual Mapping, and Mapster. Includes benchmarks and testing guidance.

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🔄 AutoMapper Mapping

// Create an AutoMapper profile for mapping Product to ProductDto
public class ProductProfile : Profile
{
    public ProductProfile()
    {
        CreateMap<Product, ProductDto>();
    }
}

⚠️ Drawback: Mapping logic is hidden and can silently break when models change.

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✅ Manual Mapping (Extension Method)

// Extension method for clean, explicit mapping from Product to ProductDto
public static class ProductMapper
{
    public static ProductDto ToDto(this Product p) =>
        new ProductDto
        {
            Id = p.Id,
            Name = p.Name,
            Price = p.Price
        };
}

✅ Benefits:

• Compile-time safety
• Refactorable and searchable in IDE
• Simple to test

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🚀 Mapster Mapping (Source Gen)

// Using Mapster's fluent config to map properties explicitly
TypeAdapterConfig<Product, ProductDto>.NewConfig()
    .Map(dest => dest.Name, src => src.ProductName)
    .Map(dest => dest.Price, src => src.Price);

⚡ Fast and clear — ideal for repetitive and performance-sensitive mapping.

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📊 Benchmark: AutoMapper vs Manual vs Mapster

// BenchmarkDotNet-based mapping performance comparison
[MemoryDiagnoser]
public class MappingBenchmarks
{
    private readonly Product _product = new() { Id = 1, Name = "Laptop", Price = 999 };

    [Benchmark]
    public ProductDto ManualMapping() => _product.ToDto(); // Fastest

    [Benchmark]
    public ProductDto MapsterMapping() => _product.Adapt<ProductDto>(); // Balanced

    [Benchmark]
    public ProductDto AutoMapperMapping()
    {
        var config = new MapperConfiguration(cfg => cfg.CreateMap<Product, ProductDto>());
        var mapper = config.CreateMapper();
        return mapper.Map<ProductDto>(_product); // Slowest
    }
}

🧪 Run it with:

BenchmarkRunner.Run<MappingBenchmarks>();

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🧪 Manual Mapping Unit Test

// Basic test to ensure mapping outputs expected values
[Fact]
public void MapsProductToDto_Correctly()
{
    var product = new Product { Id = 1, Name = "Laptop", Price = 999 };
    var dto = product.ToDto();

    dto.Id.ShouldBe(1);
    dto.Name.ShouldBe("Laptop");
    dto.Price.ShouldBe(999);
}

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🚫 AutoMapper Pitfall: Nested Mapping

public class Order { public Customer Customer { get; set; } }
public class OrderDto { public string CustomerName { get; set; } }

👎 This won't map unless nested mapping is manually configured — easy to miss.

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🧠 Reverse Mapping Trap

cfg.CreateMap<Product, ProductDto>().ReverseMap();

⚠️ ReverseMap assumes symmetrical classes. Will silently fail if types drift.

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🧨 Nullable Property Mismatch

public string? Name { get; set; } // Source
public string Name { get; set; }  // Destination

💥 No compiler error, but potential null reference runtime bugs.

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🔍 Debugging Best Practice

// Don’t map inline in LINQ Select when debugging or tracing
var dtos = products.Select(p => _mapper.Map<ProductDto>(p)); // ❌

var dtos = products.Select(p => p.ToDto()); // ✅

✅ Easier to debug, log, and maintain.

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📁 Recommended Project Structure

📦 src/
┣ 📂 Domain/
┣ 📂 Application/
┃ ┣ 📂 DTOs/
┃ ┣ 📂 Mappers/
┣ 📂 Benchmarks/
┣ 📂 Tests/

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✅ License

MIT License © Yaseer Arafat