Relationship in ASP.NET core MVC

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C#

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ASP.NET-Core

I am learning and I create this models, could you tell me where is my mistake?

public class Order
        {


            [Key]
            [Required]
            public int OrderID { get; set; }


            [Required]
            [Display(Name = "PO No:")]
            public int OrderNO { get; set; }


            [Required]
            [Display(Name = "Order Date")]
            public DateTime OrderDate { get; set; }

            public string Subject { get; set; }
            public string Status { get; set; }


            public decimal SubTotal { get; set; }
            public decimal Vat { get; set; }

            [DisplayName("Vat Amount")]
            public decimal Vatamount { get; set; }
            [DisplayName("Grand Total")]
            public decimal GrandTotal { get; set; }

            [DisplayName("Created By")]
            public string CreatedBy { get; set; }

            [DisplayName("Created Time")]
            public DateTime TimeStamp { get; set; }
        // ----------------- End Of Order Columns --------------
        public virtual ICollection<AddOrder> AddOrders { get; set; }

public class OrderDetails
    {
        [Key]
        public int OrderDetailsID { get; set; }

       
        [Range(-100000, 100000, ErrorMessage = "Quantity must be between 1 and 100000")]
        public int Qty { get; set; }

        [Range(0.01, 999999999, ErrorMessage = "Price must be between 0.01 and 999999999")]
        public decimal Price { get; set; }

             public decimal Total { get; set; }


        public virtual ICollection<AddOrder> AddOrders { get; set; }

public class POitem
    {

        [Key]
        [Required]
        public int POitemID { get; set; }

        [Required]
        [Display(Name = "Product/Service")]
        public string ItemName { get; set; }

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


        [DisplayName("Created By")]
        public string CreatedBy { get; set; }
        [DisplayName("Created Time")]
        public DateTime TimeStamp { get; set; }

        public virtual ICollection<AddOrder> AddOrders { get; set; }
    }
}

public class Project
{
[Key]
        [Required]
        public int ProjectID { get; set; }

        
        [Required][Display(Name = "Project Name")]
        public string ProjectName { get; set; }

        
        [Required][Display(Name = "Project Code")]
        public string ProjectCode { get; set; }

        
        [Required][Display(Name = "Location")]
        public string ProjectLocation { get; set; }

        
        [Required][Display(Name = "Owner")]
        public string ProjecOwner { get; set; }

        
        
        [Phone][Required][Display(Name = "Mobile")]
        public string ContactMobile { get; set; }

                
        [Required][EmailAddress][Display(Name = "Email")]
        public string Contactemail { get; set; }

        [DisplayName("Created By")]
        public string CreatedBy { get; set; }

        [DisplayName("Created Time")]
        public DateTime TimeStamp { get; set; }

        public virtual ICollection<AddOrder> AddOrders { get; set; }

    }
}

public class Supplier
    {


        
        [Key][Required]
        public int SupplierID { get; set; }

        
        [Required][Display(Name = "Supplier Name")]
        public string SupplierName { get; set; }

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

      
        [Required][Display(Name = "Adress")]
        public string Adress { get; set; }

        
        [Required][Display(Name = "Contact Person")]
        public string Contactperson { get; set; }

        
        
        [Phone][Required][Display(Name = "Mobile")]
        public string ContactMobile { get; set; }

        
        
        [Required][EmailAddress][Display(Name = "Email")]
        public string Contactemail { get; set; }

        [DisplayName("Created By")]
        public string CreatedBy { get; set; }

        [DisplayName("Created Time")]
        public DateTime TimeStamp { get; set; }


        public virtual ICollection<AddOrder> AddOrders { get; set; }

    }
}

And here is the View model code..

 public class AddOrder
    {


     

        //----------------------
    
        public int OrderID { get; set; }
        public int OrderNO { get; set; }
        public DateTime OrderDate { get; set; }
        public string Subject { get; set; }
        public string Status { get; set; }
        public decimal SubTotal { get; set; }
        public decimal Vat { get; set; }
        public decimal Vatamount { get; set; }
        public decimal GrandTotal { get; set; }
        public string CreatedBy { get; set; }
        public DateTime TimeStamp { get; set; }

        //-------------------
    
        public int POitemID { get; set; }
        public string ItemName { get; set; }
        public List<POitem> Items { get; set; }

        //------------------

        public int ProjectID { get; set; }
        public string ProjectName { get; set; }
        public string ProjectCode { get; set; }
        //------------------
   
        public int SupplierID { get; set; }
        public string SupplierName { get; set; }
        public string Contactperson { get; set; }
        public string ContactMobile { get; set; }
        public string Contactemail { get; set; }
        //------------------
  
        public int Id { get; set; }
        public string UnitName { get; set; }
        //------------------

        public int Qty { get; set; }
        public decimal Price { get; set; }
        public decimal VAT { get; set; }
        public decimal Total { get; set; }


    }
}

Here the code of ModelBuilder

protected override void OnModelCreating(ModelBuilder modelBuilder)
       {
           //Project
           modelBuilder.Entity<AddOrder>()
               .HasKey(bc => new { bc.OrderID, bc.ProjectID });
           modelBuilder.Entity<AddOrder>()
               .HasOne(bc => bc.Order)
               .WithMany(b => b.AddOrders)
               .HasForeignKey(bc => bc.OrderID);
           modelBuilder.Entity<AddOrder>()
               .HasOne(bc => bc.Project)
               .WithMany(c => c.AddOrders)
               .HasForeignKey(bc => bc.ProjectID);

           //Supplier
           modelBuilder.Entity<AddOrder>()
              .HasKey(bc => new { bc.OrderID, bc.SupplierID });
           modelBuilder.Entity<AddOrder>()
               .HasOne(bc => bc.Order)
               .WithMany(b => b.AddOrders)
               .HasForeignKey(bc => bc.OrderID);
           modelBuilder.Entity<AddOrder>()
               .HasOne(bc => bc.Supplier)
               .WithMany(c => c.AddOrders)
               .HasForeignKey(bc => bc.SupplierID);

           //POitem
           modelBuilder.Entity<AddOrder>()
              .HasKey(bc => new { bc.OrderID, bc.POitemID });
           modelBuilder.Entity<AddOrder>()
               .HasOne(bc => bc.Order)
               .WithMany(b => b.AddOrders)
               .HasForeignKey(bc => bc.OrderID);
           modelBuilder.Entity<AddOrder>()
               .HasOne(bc => bc.POitem)
               .WithMany(c => c.AddOrders)
               .HasForeignKey(bc => bc.POitemID);

           //OrderDetails
           modelBuilder.Entity<AddOrder>()
              .HasKey(bc => new { bc.OrderID, bc.OrderDetailsID });
           modelBuilder.Entity<AddOrder>()
               .HasOne(bc => bc.Order)
               .WithMany(b => b.AddOrders)
               .HasForeignKey(bc => bc.OrderID);
           modelBuilder.Entity<AddOrder>()
               .HasOne(bc => bc.OrderDetails)
               .WithMany(c => c.AddOrders)
               .HasForeignKey(bc => bc.OrderDetailsID);


           //Unit
           modelBuilder.Entity<AddOrder>()
              .HasKey(bc => new { bc.OrderID, bc.UnitID });
           modelBuilder.Entity<AddOrder>()
               .HasOne(bc => bc.Order)
               .WithMany(b => b.AddOrders)
               .HasForeignKey(bc => bc.OrderID);
           modelBuilder.Entity<AddOrder>()
               .HasOne(bc => bc.Unit)
               .WithMany(c => c.AddOrders)
               .HasForeignKey(bc => bc.UnitID);
       }

Is this correct way , please advice

What I have tried:

Read many articles and document, but I believe that I missed somthing