EF Navigation properties with fluent API

Question

I have never used navigation properties before, so I'm trying to understand how they work. I prefer to map them via fluent API as a matter of preference. Can someone please explain to me how to set this relationship up using fluent API ?

public class FooA
{
    [Key]
    public int FooAID {get;set;}
    [Required]
    public String NameA {get;set;}

}

public class FooB
{
    [Key]
    public int FooBID {get;set;}
    [Required]
    public String NameB {get;set;}

    public int? FooA_FK1 {get;set;}
    public int? FooA_FK2 {get;set;}

    [ForeignKey("FooA_FK1")]
    public virtual FooA Nav_FK1{get;set;}

    [ForeignKey("FooA_FK2")]
    public virtual FooA Nav_FK2{get;set;}
}

/*
Note that FooB has TWO NULLABLE (Optional?) references to FooA objects.
Also, the foreign key names don't follow the convention for EF.

I want to understand the fluent API used to construct this type of relationship.

I have been able to use fluent API to get this set up provided that the items
are required.  When I tried using the .HasOptional() method, I got an exception.

*/

Answer 1

With that model you are creating two one-to-many relationships, but both are unidirectionals (you don't declare a navigation property in one of the relationship's end). The equivalent Fluent Api configurations- overriding the OnModelCreating method on your context- are this:

modelBuilder.Entity<FooB>().HasOptional(fb=>fb.Nav_FK1).WithMany().HasForeignKey(fb=>fb.FooA_FK1);
modelBuilder.Entity<FooB>().HasOptional(fb=>fb.Nav_FK2).WithMany().HasForeignKey(fb=>fb.FooA_FK2);

In this link you will find more info about how to create different kind of relationships using Fluent Api.

Answer 2

If your foreign key is nullable you could use HasOptional in your fluent api relationship definitions:

HasOptional(a => a.Nav_FK1).WithMany().HasForeignKey(b => b.FooA_FK1);

HasOptional(a => a.Nav_FK2).WithMany().HasForeignKey(b => b.FooA_FK2);

Reference: http://www.entityframeworktutorial.net/code-first/configure-one-to-one-relationship-in-code-first.aspx