AutoMapper now supports attributes natively. Don't use this library. More documentation here: https://docs.automapper.org/en/stable/Attribute-mapping.html

I also wrote about my experience writing this library here.

AutoMapper.Attributes

A convenient way to create AutoMapper type mappings using attributes.

Why use AutoMapper.Attributes?

• Self-documenting code - mappings become more obvious to developers since they are attached directly to the type
• Simple, intuitive API for mapping objects
• Allows for dot notation of mapping properties
• Works with AutoMapper 5+ (including 6)

How to use

1. Create the classes you'd like to map.
2. Add the [MapsTo] attribute to the source class, with the target type as the argument. (Alternatively, you can use the [MapsFrom] attribute to map the target class with the source type.)
3. Call the MapTypes() extension method on the assembly from which you want to map your types when you call Mapper.Initialize.
4. You're done!

Sample

public class Program
{
    public void Main()
    {
        AutoMapper.Mapper.Initialize(config => {
            typeof(Program).Assembly.MapTypes(config);      //or use typeof(Program).GetTypeInfo().Assembly if using .NET Standard
        });
        
        var person = new Person { FirstName = "John", LastName = "Lackey" };
        var customer = AutoMapper.Mapper.Map<Customer>(person);
        
        Console.WriteLine(customer.LastName);
        // Output: Lackey
    }

    [MapsTo(typeof(Customer))]
    public class Person 
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Notes { get; set; }
    }

    public class Customer
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string MyCustomerNotes { get; set; }
    }
}

Mapping properties

AutoMapper's built-in property mapping works for 90% of use cases. But what if you need to map two properties with different names, or even a property that is a few classes deep? There are two attributes made for this - [MapsFromProperty] and [MapsToProperty]. Both take a type and a name of a property you want to map from/to. These attributes support nested property mapping using dot notation.

[MapsFromProperty(typeof(SourceType), "Address.City")]

MapsToProperty example

[MapsToProperty] allows you to designate a source type's property as mapping to a target type's property. Simply:

1. Define your source class (in this example, Person)
2. Define your target class (in this example, Customer)
3. Define your source class properties
4. Add the [MapsToProperty] to the property that you want to map to the target property. In this case, the attribute's arguments are the target type and the name of the target type's property.

Sample

public class Program
{
    public void Main()
    {
        AutoMapper.Mapper.Initialize(config => {
            typeof(Program).Assembly.MapTypes(config);
        });

        var person = new Person { Notes = "these are some notes" };
        var customer = AutoMapper.Mapper.Map<Customer>(person);
        
        Console.WriteLine(customer.MyCustomerNotes);
        // Output: these are some notes
    }

    [MapsTo(typeof(Customer))]
    public class Person 
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        [MapsToProperty(typeof(Customer), "MyCustomerNotes")]
        public string Notes { get; set; }
    }

    public class Customer
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string MyCustomerNotes { get; set; }
    }
}

MapsFromProperty example

[MapsFromProperty] allows you to designate a target type's property as mapping to a source type's property. Simply:

1. Define your source class (in this example, Person)
2. Define your target class (in this example, Customer)
3. Define your source class properties
4. Add the [MapsFromProperty] to the target type's property that you want to map to the source property. In this case, the attribute's arguments are the source type and the name of the source type's property.

Sample

public class Program
{
    public void Main()
    {
        AutoMapper.Mapper.Initialize(config => {
            typeof(Program).Assembly.MapTypes(config);
        });

        var person = new Person { Notes = "these are some more notes" };
        var customer = AutoMapper.Mapper.Map<Customer>(person);
        
        Console.WriteLine(customer.MyCustomerNotes);
        // Output: these are some more notes
    }

    public class Person 
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Notes { get; set; }
    }

    [MapsFrom(typeof(Person))]
    public class Customer
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        [MapsFromProperty(typeof(Person), "Notes")]
        public string MyCustomerNotes { get; set; }
    }
}

Two-way mapping

Use [MapsToAndFromProperty] to tell the mapper to bind the source type's property to the target type's property and back.

1. Define your source class (in this example, Person)
2. Define your target class (in this example, Customer)
3. Define your source class properties
4. Add the [MapsFromProperty] to the source or target type's property that you want to map to the other type's property.

Ignoring properties

You can use the following attributes to ignore properties on a target type or a source type.

IgnoreMapFrom

Use the [IgnoreMapFrom] attribute on a target type's property to ignore all properties from the source type.

Sample

public class Person 
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Notes { get; set; }
}

[MapsFrom(typeof(Person))]
public class Customer
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    [IgnoreMapFrom(typeof(Person))]     //Notes will not be set from type Person
    public string Notes { get; set; }
}

IgnoreMapToProperties

Use the [IgnoreMapToProperties] attribute on your source type to ignore one or more properties on the target type. This must be added to the type itself and cannot be added to properties due to a limitation of AutoMapper - see: AutoMapper/AutoMapper#1556

Sample

//Notes and Costs will not 
[IgnoreMapToProperties(typeof(Customer), nameof(Customer.Notes), nameof(Customer.Costs))]
public class Person 
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Notes { get; set; }
    public decimal Costs { get; set; }
}

[MapsFrom(typeof(Person))]
public class Customer
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Notes { get; set; }
    public decimal Costs { get; set; }    
}

Ok, but I need some super custom mapping behavior.

No problem - you can create a subclass of MapsToAttribute and add a method called ConfigureMapping method with the type arguments specified explicitly for IMappingExpression. As long as the method is named ConfigureMapping (case sensitive!) and the method signature uses the exact same type arguments as the classes you're mapping, you can configure the mapping to your heart's content:

public class MapsToCustomer : MapsToAttribute
{
    public MapsToCustomer() : base(typeof(Customer)) {}

    public void ConfigureMapping(IMappingExpression<Person, Customer> mappingExpression)
    {
        mappingExpression.ForMember(d => d.CustomerNotes, expression => expression.MapFrom(s => s.Notes));
    }
}

What else you got?

• The examples above make heavy use of the [MapsTo] attribute, but don't forget you have a [MapsFrom] attribute as well!
• You can set the ReverseMap property in the [MapsTo]/[MapsFrom] attribute to true if you want to map the classes in reverse as well, like this:

[MapsTo(typeof(Customer), ReverseMap = true)]    //this will map Customer to Person and Person to Customer
public class Person {...}

License

This project is licensed under the MIT license.

Author info

Made with <3 by Spencer Schneidenbach

Twitter @schneidenbach
Website https://schneids.net