实体框架 6 多重性无效？

Question

I have two tables where I want to implement a 1-1 relationship.I run into a issue described in this post: EntityFramework : Invalid column name *_ID1 I tried to implement the solution,to add the Foreign Key attribute and I run into another issue:

Multiplicity is not valid in Role 'Account_Companies_Target' in relationship 'Account_Companies'. Because the Dependent Role properties are not the key properties, the upper bound of the multiplicity of the Dependent Role must be '*'.

These are the classes:

 public class Account
{
    [Key]
    public Guid Id { get; set; }
    public string CompanyName { get; set; }
    public long CNP { get; set; }
    public string Name { get; set; }
    public string Surname { get; set; }
    public long PhoneNumber { get; set; }
    public string Address { get; set; }
    [Required]
    public string UserName { get; set; }

    [Required(ErrorMessage = "Password is Required.")]
    public string Password { get; set; }
    public DateTime CreatedOn { get; set; }

    [NotMapped]
    [Required(ErrorMessage = "Confirmation Password is Required")]
    [Compare("Password", ErrorMessage = "Password Must Match")]
    public string ConfirmPassword { get; set; } 

    [Required]
    public AccountType AccountType { get; set; }

    public int CUI { get; set; }

    [ForeignKey("Id")]
    public virtual Company Companies { get; set; }

}

   public class Company
{

    [Key]
    public long CUI { get; set; }
    public Guid Id { get; set; }
    public string CompanyName { get; set; }
    public string Simbol { get; set; }
    public int SharesCount { get; set; }
    public decimal SharePrice { get; set; }
    public virtual Account Account { get; set; }

}

and this is the OnModelCreating overide:

  protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Account>()
           .HasOptional(account => account.Companies)
           .WithRequired(company => company.Account);            
    }

Answer 1

If Account.CUI, the foreign key property, is not a key, then the relationship is 1:many, not 1:1. And EF6 only allows an entity to have one key.