Tutorial: Standalone Mapping with [AutoMap]

In AutoMappic v0.6.0+, you can define mappings directly on your DTO or Entity classes using the [AutoMap] attribute. This "standalone" approach is perfect for reducing boilerplate when you don't need the complex configuration of a full Profile class.

1. Quick Start

Instead of creating a separate mapping profile, decorate your destination class with [AutoMap] and specify the source type.

using AutoMappic;

// The Source
public sealed class UserRecord 
{ 
    public int Id { get; init; } 
    public string Name { get; init; } 
}

// THE STANDALONE DTO
[AutoMap(typeof(UserRecord))]
public partial class UserDto 
{ 
    public int Id { get; set; } 
    public string Name { get; set; } 
}

2. The partial Requirement

For standalone mapping to work, your class must be marked as partial.

Why? Because the AutoMappic Source Generator identifies classes with [AutoMap] and generates matching mapping methods directly inside a sibling partial class at compile time. This ensures zero reflection and full Native AOT compatibility.

💡 IDE Support: The Automatic Code-Fix

If you forget to add the partial keyword, AutoMappic will report a diagnostic error (AM0018). In Visual Studio or VS Code, you can simply click the Lightbulb 💡 (or press Ctrl+.) and select "Add partial keyword" to fix it automatically.

3. Configuration Options

The [AutoMap] attribute allows you to configure advanced features just like a Profile:

Option	Description
ReverseMap	Automatically generates the reverse mapping from DTO back to Source.
EnableIdentityManagement	Opts-in to object reference tracking (prevents circularity).
DeleteOrphans	Automatically removes items from child collections if they aren't in the source.
SourceNamingConvention	Overrides how source property names are interpreted (e.g., SnakeCaseNaming).

Example: Bi-directional Entity Sync

[AutoMap(typeof(User), ReverseMap = true, EnableIdentityManagement = true)]
public partial class UserDto 
{ 
    public string Email { get; set; }
}

4. How it is Discovered

You don't need to manually register standalone mappings. When you call services.AddAutoMappic(), the engine automatically scans for all classes decorated with [AutoMap] and registers them into the global IMapper.

// Usage remains identical to Profile-based mapping
var userDto = mapper.Map<UserDto>(user);

5. When to use [AutoMap] vs. Profile

• Use [AutoMap]: For standard DTOs where property names match or use standard flattening. It keeps your code localized and easy to read.
• Use Profile: When you need complex logic like .ForMember(), .AfterMap(), or custom ITypeConverter implementations that require access to the mapping expression tree.

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