entity framework - EF Code First foreign key without navigation property

Question

Let's say I have the following entities:

public class Parent
{
    public int Id { get; set; }
}
public class Child
{
    public int Id { get; set; }
    public int ParentId { get; set; }
}

What is the code first fluent API syntax to enforce that ParentId is created in the database with a foreign key constraint to the Parents table, without the need to have a navigation property?

I know that if I add a navigation property Parent to Child, then I can do this:

modelBuilder.Entity<Child>()
    .HasRequired<Parent>(c => c.Parent)
    .WithMany()
    .HasForeignKey(c => c.ParentId);

But I don't want the navigation property in this particular case.

Answer 1

Although this post is for Entity Framework not Entity Framework Core, It might be useful for someone who wants to achieve the same thing using Entity Framework Core (I am using V1.1.2).

I don't need navigation properties (although they're nice) because I am practicing DDD and I want Parent and Child to be two separate aggregate roots. I want them to be able to talk to each other via foreign key not through infrastructure-specific Entity Framework navigation properties.

All you have to do is to configure the relationship on one side using HasOne and WithMany without specifying the navigation properties (they're not there after all).

public class AppDbContext : DbContext
{
    public AppDbContext(DbContextOptions<AppDbContext> options) : base(options) {}

    protected override void OnModelCreating(ModelBuilder builder)
    {
        ......

        builder.Entity<Parent>(b => {
            b.HasKey(p => p.Id);
            b.ToTable("Parent");
        });

        builder.Entity<Child>(b => {
            b.HasKey(c => c.Id);
            b.Property(c => c.ParentId).IsRequired();

            // Without referencing navigation properties (they're not there anyway)
            b.HasOne<Parent>()    // <---
                .WithMany()       // <---
                .HasForeignKey(c => c.ParentId);

            // Just for comparison, with navigation properties defined,
            // (let's say you call it Parent in the Child class and Children
            // collection in Parent class), you might have to configure them 
            // like:
            // b.HasOne(c => c.Parent)
            //     .WithMany(p => p.Children)
            //     .HasForeignKey(c => c.ParentId);

            b.ToTable("Child");
        });

        ......
    }
}

I am giving out examples on how to configure entity properties as well, but the most important one here is HasOne<>, WithMany() and HasForeignKey().

Hope it helps.