Onion Architecture- Entity Framework Code First Models DataAnnotations

Question

I am developing a ASP.NET MVC Project following the Onion Architecture. I have added the Models inside my Core Project and these Models will be referred as the POCO classes

Answer 1

You don't need to create Core Models as Interfaces if you switch from Data Annotations the Fluent API.

Here's an example.

The Entity1 object is a core layer domain object:

namespace MyApp.Core.Model
{
  public class Entity1
  {
    public short Id { get; set; }
    public string ExternalCode { get; set; }
    public byte Status { get; set; }
  }
}

In the infrastructure layer, create an Entity1Mapping class where you'll do what you'd have done using Data Annotation, but this time, with the Fluent API instead:

using System.Data.Entity.ModelConfiguration;

namespace MyApp.Infrasrtucture.Data.Configuration
{
  internal class Entity1Mapping : EntityTypeConfiguration<Core.Model.Entity1>
  {
     internal Entity1Mapping()
     {
       HasKey(g => g.Id);
       Property(g => g.Id).IsRequired();

       Property(g => g.ExternalCode)
           .IsRequired()
           .HasMaxLength(100)
           .IsVariableLength()
           .IsUnicode(false);

       Property(g => g.Status).HasColumnName("EntityStatus").IsRequired();
     }
  }
}

Last thing you have to do, is adding the mapping in the modelBuilder of your context:

using System.Data.Entity;

namespace MyApp.Infrastructure.Data
{
  public class MyContext : DbContext, IDbContext
  {
    public MyContext() : base("ConnectionStringMyContext")
    { }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
      Database.SetInitializer<MyContext>(null);
      modelBuilder.Configurations.Add(new Configuration.Entity1Mapping());
    }
  }
}

This is the IDBContext just in case:

public interface IDbContext
{
  DbSet<T> Set<T>() where T : class;
  DbEntityEntry<T> Entry<T>(T entity) where T : class;
  int SaveChanges();
  void Dispose();
}

Answer 2

Using FluentAPI is a good a solution in my opinion.

It is worth noting though that System.Component.DataAnnotations does not rely on EntityFramework - so you can use DataAnnotations in your core project and still be agnostic on your particular persistance mechanism.