Post_11_1.cs

public class Category
{
  public int Id { get; set; }
  public string Name { get; set; }

  public ICollection<Article> Articles { get; set; }
}

public class Article
{
  public int Id { get; set; }
  public int CategoryId { get; set; }
  public string Name { get; set; }
  public string Description { get; set; }
  public decimal Price { get; set; }
  public DateTime Created { get; set; }

  public virtual Category Category { get; set; }
  public virtual ICollection<Photo> Photos { get; set; }
}

public class Photo
{
  public int Id { get; set; }
  public int ArticleId { get; set; }
  public string Filename { get; set; }
  public bool IsDefault { get; set; }

  public virtual Article Article { get; set; }
}