Attribute Mapper ([MapTo])

EggMapper.Generator generates zero-reflection, zero-allocation extension methods at build time from a single [MapTo] attribute. No MapperConfiguration, no runtime delegates — the mapping code is emitted directly into your binary.

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Installation

dotnet add package EggMapper.Generator

The generator package automatically injects the [MapTo], [MapProperty], and [MapIgnore] attributes into your compilation — no separate abstractions package needed.

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Basic Usage

1 — Annotate the source class

using EggMapper;

[MapTo(typeof(OrderDto))]
public class Order
{
    public int    Id           { get; set; }
    public string CustomerName { get; set; } = "";
    public decimal Total       { get; set; }
}

public class OrderDto
{
    public int    Id           { get; set; }
    public string CustomerName { get; set; } = "";
    public decimal Total       { get; set; }
}

2 — Use the generated extension method

var order = new Order { Id = 1, CustomerName = "Alice", Total = 99.99m };
OrderDto dto = order.ToOrderDto();               // generated extension method
List<OrderDto> dtos = orders.ToOrderDtoList();   // generated list method

No mapper instance, no DI registration, no startup cost.

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Multiple Destinations

Apply [MapTo] multiple times to map a single source to several destinations:

[MapTo(typeof(OrderDto))]
[MapTo(typeof(OrderSummary))]
public class Order { ... }

Generates ToOrderDto(), ToOrderDtoList(), ToOrderSummary(), and ToOrderSummaryList().

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Renaming Properties ([MapProperty])

[MapTo(typeof(CustomerDto))]
public class Customer
{
    public int    Id   { get; set; }

    [MapProperty("FullName")]   // maps Customer.Name → CustomerDto.FullName
    public string Name { get; set; } = "";
}

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Ignoring Properties ([MapIgnore])

[MapTo(typeof(CustomerDto))]
public class Customer
{
    public int    Id       { get; set; }
    public string Name     { get; set; } = "";

    [MapIgnore]
    public string Password { get; set; } = "";  // not copied to CustomerDto
}

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Post-Map Hook (AfterMap)

Declare a partial static method to run custom logic after the generated initializer:

// In a separate file (user-authored):
public static partial class OrderToOrderDtoExtensions
{
    static partial void AfterMap(Order source, OrderDto dest)
    {
        dest.DisplayName = $"#{source.Id} — {source.CustomerName}";
    }
}

The generated ToOrderDto() calls AfterMap(source, dest) after building the object.

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Diagnostics

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When to Use Attribute Mapper vs Runtime EggMapper