MapTo/README.md

# MapTo
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A convention based object to object mapper using [Roslyn source generator](https://github.com/dotnet/roslyn/blob/master/docs/features/source-generators.md).

MapTo creates mappings during compile-time, which eliminates the need for using reflection to create the mappings. This makes it super simple to use and way faster than other libraries.

## Installation
```
dotnet add package MapTo --prerelease
```

## Usage
To generate the mappings, simply declare the destination class as `partial` and annotate it with `MapFrom` attribute.

```c#
using MapTo;

namespace App.ViewModels
{
    [MapFrom(typeof(App.Data.Models.User))]
    public partial class UserViewModel 
    {
        public string FirstName { get; }
    
        public string LastName { get; }
        
        [IgnoreProperty]
        public string FullName { get; set; }
    }
}
```

## Generated Source
In the above example, if `App.Data.Models.User` class is defined as:

```c#
namespace App.Data.Models
{
    public class User
    {
        public User(int id) => Id = id;
        
        public int Id { get; }

        public string FirstName { get; set; }

        public string LastName { get; set; }

        public string FullName => $"{FirstName} {LastName}";
    }
}
```

It will generate the following code:

```c#
// <auto-generated />
using System;

namespace App.ViewModels
{
    public partial class UserViewModel
    {
        public UserViewModel(App.Data.Models.User user)
        {
            if (user == null) throw new ArgumentNullException(nameof(user));
            
            FirstName = user.FirstName;
            LastName = user.LastName;
        }

        public static UserViewModel From(App.Data.Models.User user)
        {
            return user == null ? null : new UserViewModel(user);
        }
    }

    public static partial class UserToUserViewModelExtensions
    {
        public static UserViewModel ToUserViewModel(this App.Data.Models.User user)
        {
            return user == null ? null : new UserViewModel(user);
        }
    }
}
```

Which makes it possible to get an instance of `UserViewModel` from one of the following ways:

```c#
var user = new User(id: 10) { FirstName = "John", LastName = "Doe" };

var vm = user.ToUserViewModel();

// OR
vm = new UserViewModel(user);

// OR
vm = UserViewModel.From(user);
```