在EF4代码优先中，如何使一个实体的主键成为另一个实体？

Question

Say I have a Post entity, and I want to store all changes to post objects, so I also have a PostHistory entity. Right now I would define the history as something like this:

public class PostHistory
{
   public virtual Post Post { get; set; }

   //... properties of the posthistory object
}

The problem is I can't figure out how to get this to work with EF4 Code-First. At first model building fails because there is no primary key defined for PostHistory . So in my Context I call

modelBuilder.Entity<PostHistory>().HasKey(x => x.Post);

And the following exception occurs:

System.MissingMethodException: No parameterless constructor defined for this object..

That exception is not talking about the PostHistory object not having a parameterless constructor, because I added one and it didn't help.

Any ideas how to accomplish this?

Answer 1

public class Post {
    [Key, DatabaseGenerated(DatabaseGenerationOption.Identity)]
    public int Id { get; set; }

    public virtual ICollection<PostHistory> Histories { get; set; }
}

public class PostHistory {
    [Key, DatabaseGenerated(DatabaseGenerationOption.Identity)]
    public int Id { get; set; }

    public int PostId { get; set; }
    public virtual Post Post { get; set; }

   //... properties of the posthistory object
}