title: One-to-many relationship between applicationuser and custom entity
body: <p>I get an error that says "ApplicationUser_Cars_Target: : Multiplicity is not valid in Role 'ApplicationUser_Cars_Target' in relationship 'ApplicationUser_Cars'. Because the Dependent Role properties are not the key properties, the upper bound of the multiplicity of the Dependent Role must be '*'.
  "
  when I try to update my database, here is my code:</p>
  
  <pre><code>public class ApplicationUser : IdentityUser
  {
      public string ProfilePicture { get;set; }
      public string FirstName { get; set; }
      public string LastName { get; set; }
      public int PhoneNumber1 { get; set; }
      public int PhoneNumber2 { get; set; }
      public Address Address { get; set; }
      [ForeignKey("Cars")]
      public int CarId { get; set; }
      public ICollection&lt;Car&gt; Cars { get; set; }
  }
  
  
  public class Car
  {
      [Key]
      public int CarId { get; set; }
      [ForeignKey("User")]
      public string ApplicationUserId { get; set; }
      public string Make { get; set; }
      public string Registration { get; set; }
      public string Color { get; set; }
      public string Model { get; set; }
      public string Year { get; set; }
      public string Type { get; set; }
      public virtual ApplicationUser User { get; set; }
  }
  </code></pre>
  
  <p>and this is the fluent api requirement I have... It should be optional for users to register a car  </p>
  
  <pre><code>        modelBuilder.Entity&lt;ApplicationUser&gt;().HasKey(x =&gt; x.Id)
              .HasOptional(x =&gt; x.Cars);
  </code></pre>