Fluent API: defining one to many

   public class Customer
 {
     public int Id { get; set; }
     public string Name { get; set; }
     public string Contact { get; set; }
     public ICollection<ShippingAddress> ShippingAddressNavigation { get; set; } = new List<ShippingAddress>();
 }
   public class ShippingAddress
  {
      public int Id { get; set; }
      public string Address { get; set; }
      public int CustomerId { get; set; }
      public Customer CustomerNavigation { get; set; }

  }

 public class CustomerMapping : IEntityTypeConfiguration<Customer>
 {
     public void Configure(EntityTypeBuilder<Customer> builder)
     {
         builder.ToTable("customers");
         builder.HasKey(c => c.Id);
         builder.HasMany<ShippingAddress>(c => c.ShippingAddressNavigation).WithOne(s => s.CustomerNavigation).HasForeignKey(s => s.CustomerId);
     }
 }
 
  public class ShippingAddressMapping : IEntityTypeConfiguration<ShippingAddress>
  {
      public void Configure(EntityTypeBuilder<ShippingAddress> builder)
      {
          builder.ToTable(nameof(ShippingAddress));
          builder.HasKey(s=>s.Id);
          builder.HasOne<Customer>(S => S.CustomerNavigation).WithMany(c => c.ShippingAddressNavigation).HasForeignKey(a=>a.CustomerId);
      }
  }