在没有所有键/外键的情况下在实体框架中创建导航属性

Question

I have been trying to figure out if it is possible to create an association in EF without the use of all keys.

Below is an example where there is a combination key in author, but I only have 1 part of that key in book. My question is how do I make a Navigation property without all of the keys?

[Table("Book")]
public class Book {

    [Key]
    public int ID { get; set; }

    public string AuthorLastName { get; set; }

    public virtual Author Author { get; set; }
}

[Table("Author")]
public class Author {

    [Key, Column(Order=0)]
    public string AuthorFirstName { get; set; }

    [Key, Column(Order=1)]
    public string AuthorLastName { get; set; }

    public virtual ICollection<Book> Books { get; set; }
}

internal class BookConfig : EntityTypeConfiguration<Book> {
    public BookConfig()
    {
        HasRequired(hr => hr.Author)
            .WithMany(wm => wm.Books)
            .HasForeignKey(fk => new { 
                fk.AuthorLastName
            });
    }
}

This is obviously not going to work since I don't have all of the full combination key in book to associate it to author in this way.

Answer 1

You can do something like that:

[Key]
[DatabaseGenerated(DatabaseGeneratedOption.None)]
public int ID { get; set; }

This will give you a manual control on the key; But the Table in the database must have a primary key! I'm wonderung why ou need something like that I think the problem somewhere else.

Answer 2

You cannot do that because it's a many to many relation.

In your example, if you only take AuthorLastName there can be several authors with the same last name. So there are many elements in this side of the relation. And obviously there are many books on the other side (an author can write many books).

So, definitely, you cannot model it as a one-to-many relation.

Fortunately, someone has explained this problem of books and authors before. .