EF AutoMapper Map Entities to DTOs

In multi-layered architectures like client-server applications, data is usually represented differently at each layer. In such architectures, communicating between layers may become cumbersome.

• You can avoid this and simplifies the communication by using the DTO pattern, which involves defining simple classes to transfer data between layers.
• DTOs are exactly what they sound like, a construct designed to pass data from one system to another, nothing more and nothing less.

The main issue that comes with this approach is that it requires writing a large amount of mapping code, which is an error-prone and tedious task.

Now let's define a DTO for an author and book entities which we will map to the Author and Book entities respectively.

public class AuthorDTO
{
    public int AuthorId { get; set; }
    public string Name { get; set; }
    public string Country { get; set; }
    public virtual ICollection<BookDTO> Books { get; set; }
}

public class BookDTO
{
    public int Id { get; set; }
    public string Title { get; set; }
    public int NoOfPages { get; set; }
    public string Category { get; set; }
    public int AuthorId { get; set; }
    public AuthorDTO Author { get; set; }
}

AutoMapper provides a MapperConfiguration where you can specify the mappings between entities and their DTOs.

var config = new MapperConfiguration(cfg => {
    cfg.CreateMap<Author, AuthorDTO>();
    cfg.CreateMap<Book, BookDTO>();
});

AutoMapper.EF6 provides a set of extension methods that perform the conversion very easily.

Let's consider the following simple example in which the author entities are returned as DTOs as shown below.

using (var context = new BookStore())
{
    var config = new MapperConfiguration(cfg => {
        cfg.CreateMap<Author, AuthorDTO>();
        cfg.CreateMap<Book, BookDTO>();
    });

    var authors = context.Authors.ProjectToList<AuthorDTO>(config);

    Console.WriteLine("Total Authors: {0}", authors.Count);
}