EF Code First Entity Mapping with Foreign Key in Mapped Entity - entity-framework

Question

(source: mcainsh.info)
The tables are just for an example, what I am trying to do is map a virtual Manufacturer in the Book entity. I've tried using data annotation similar to below:
[ForeignKey("PublisherId")]
public virtual Publisher { get; set; }
[ForeignKey("Publisher.ManufacturerCompanyId")]
[InverseProperty("ManufacturerId")]
public virtual Manufacturer { get; set; }
Is this something that can be done?

Answer 1

You're configuring incorrectly the foreign keys. To do what you want, your model should be like this:
public class Book
{
public int Id { get; set; }
public string Title{ get; set; }
public int PublisherId { get; set; }
[ForeignKey("PublisherId")]
public virtual Publisher Publisher{ get; set; }
public int ManufacturerId { get; set; }
[ForeignKey("ManufacturerId")]
public virtual Manufacturer Manufacturer { get; set; }
}
public class Manufacturer
{
public int Id { get; set; }
public string Name { get; set; }
}
public class Publisher
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Book> Books { get; set; }
}
In this model you have two one-to-many relationships, the first between Book and Publisher and the second one between Book and Manufacturer. As you can see in the Book class, if you want to use a FK property you must declare a property of the same type of the PK of the related entity (see PublisherId and ManufacturerId).Now, you can apply the ForeignKey annotation to the navigation property and tell it which property is the foreign key for the relationship, as I show above. Alternatively, you can addForeignKey attribute to the ManufacturerId, along with information telling it which navigation property represents the relationship it is a foreign key for:
[ForeignKey("Manufacturer")]
public int ManufacturerId { get; set; }
public virtual Manufacturer Manufacturer { get; set; }
If you want, you don't need to create the FKs properties, EF will do the job for you begin the escene. It will create a FK row in your Books table for each relationship (check the DB after execute your code):
public class Book
{
public int Id { get; set; }
public string Title{ get; set; }
//public int PublisherId { get; set; }
//[ForeignKey("PublisherId")]
public virtual Publisher Publisher{ get; set; }
//public int ManufacturerId { get; set; }
//[ForeignKey("ManufacturerId")]
public virtual Manufacturer Manufacturer { get; set; }
}