Entity framework code-first null foreign key

You must make your foreign key nullable:

public class User
{
    public int Id { get; set; }
    public int? CountryId { get; set; }
    public virtual Country Country { get; set; }
}

I prefer this (below):

public class User
{
    public int Id { get; set; }
    public int? CountryId { get; set; }
    [ForeignKey("CountryId")]
    public virtual Country Country { get; set; }
}

Because EF was creating 2 foreign keys in the database table: CountryId, and CountryId1, but the code above fixed that.

I have the same problem now , I have foreign key and i need put it as nullable, to solve this problem you should put

    modelBuilder.Entity<Country>()
        .HasMany(c => c.Users)
        .WithOptional(c => c.Country)
        .HasForeignKey(c => c.CountryId)
        .WillCascadeOnDelete(false);

in DBContext class I am sorry for answer you very late :)