Entity Framework - Foreign keys and Navigation Properties

Question

I need your help understanding relationships between tables. I´m having a hard time trying to understand the usage/need of using navigation properties with foreign key properties to define relantionships. Given the 2 classes below,

public class Person
{
        [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public Guid Id { get; set; }

        [Required]
        public string Name{ get; set; }
}

public class Package
{
        [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public Guid Id { get; set; }

        [Required]
        public Guid AccountId { get; set; }
        public virtual Person Account { get; set; }

        public Guid ShipperId { get; set; }
        public virtual Client Shipper { get; set; }

        [Required]
        public Guid ReceiverId { get; set; }
        public virtual Client Receiver { get; set; }

}

If I try to update the database, I get the error

Introducing FOREIGN KEY constraint 'FK_' on table 'Packages' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.

On the other hand if I remove the property public Guid ....Id { get; set; }, the database is created with the foreign keys but the [Required] annotation as no effect.

What´s the difference between including a Guid property and not?

Answer 1

try to use this classes:

 public class Person
    {
        [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public Guid Id { get; set; }

        [Required]
        public string Name{ get; set; }

        [InverseProperty(nameof(Package.Account))]
        public virtual ICollection<Package> Packages { get; set; }

    }

    public class Package
    {
        
        [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public Guid Id { get; set; }

        [Required]
        public Guid AccountId { get; set; }
       
        [ForeignKey(nameof(AccountId))]
        [InverseProperty("Packages")]
        public virtual Person Account { get; set; }
    }

and use this code in dbcontext:

modelBuilder.Entity<Package>(entity =>
{
    entity.HasOne(d => d.Person)
    .WithMany(p => p.Packages)
    .HasForeignKey(d => d.AccountId)
    .OnDelete(DeleteBehavior.ClientSetNull);

});