Related data in tables using Entity Framework

Question

I have a question on related data in tables using Entity Framework. I have 2 tables "customer" && "customerpreferences", since both tables have customer, then the primary key is "Id_Cus". I reviewed eager, lazy loading. It was decided to use eager loading. My service implements the REST architecture on WCF. I would like to know whether it is necessary to write (Include (a => a.customerpreferences)) in each of the methods. And another question, in the screenshots attached below, I checked out where I inserted the expression described above, but this did not work, could you tell me where to put this expression. Thank you in advance!

My code for 3rd image

   using System;
   using System.Collections.Generic;
   using System.Linq;
   using System.Runtime.Serialization;
   using System.ServiceModel;
   using System.Text;
   using MySql.Data;
   using System.Data.Entity;

   using WcfRestFullService.Model;

   namespace WcfRestFullService
   {
    // NOTE: You can use the "Rename" command on the "Refactor" menu to change 
    the class name "CustomerSevice" in code, svc and config file together.
    // NOTE: In order to launch WCF Test Client for testing this service, 
    please select CustomerSevice.svc or CustomerSevice.svc.cs at the Solution 
    Explorer and start debugging.
    public class CustomerSevice : ICustomerSevice
    {
        MySQLEntities dc;
        public CustomerSevice()
        {
            dc = new MySQLEntities();
        }

        public List<customer> GetAllCustomer()
        {
            var query = (from a in dc.customers
                         select a).Include(c=>c.customerpreference).Distinct();

            List<customer> CustomersList = new List<customer>();

            query.ToList().ForEach(x =>
            {
                CustomersList.Add(new customer
                {
                    Id_Cus = x.Id_Cus,
                    FirstName_Cus = x.FirstName_Cus,
                    LastName_Cus = x.LastName_Cus,
                    PhoneNum_Cus = x.PhoneNum_Cus,
                    Email_Cus = x.Email_Cus,
                });
            });
            return CustomersList;
        }

        public customer CustomerDetails(string Id_Cus)
        {
            customer Cust = new customer();
            try
            {
                var query = (from a in dc.customers
                             where a.Id_Cus.Equals(Id_Cus)
                             select a).Distinct().FirstOrDefault();
                Cust.Id_Cus = query.Id_Cus;
                Cust.FirstName_Cus = query.FirstName_Cus;
                Cust.LastName_Cus = query.LastName_Cus;
                Cust.PhoneNum_Cus = query.PhoneNum_Cus;
                Cust.Email_Cus = query.Email_Cus;
            }
            catch (Exception ex)
            {
                throw new FaultException<string>(ex.Message);
            }
            return Cust;
        }

        // DELETE

        public void DeleteCustomer(string Id_Cus)
        {
            //MySQLEntities Cust = new MySQLEntities(); //check the file 
        Model.edmx->ModelContext.tt->MySQLEntitys

            int k = Convert.ToInt32(Id_Cus);
            customer cur = (from n in dc.customers
                            where n.Id_Cus == k
                            select n).ToList().First();

            dc.Configuration.ValidateOnSaveEnabled = false;
            dc.customers.Remove(cur);
            dc.SaveChanges();
        }

        //Insert/POST

        public void InsertCustomer(customer customerDataContract)
        {
            //MySQLEntities Cust = new MySQLEntities();
            customer cust = new customer();

            cust.Id_Cus = Convert.ToInt32(customerDataContract.Id_Cus);
            cust.FirstName_Cus = customerDataContract.FirstName_Cus;
            cust.LastName_Cus = customerDataContract.LastName_Cus;
            cust.PhoneNum_Cus = 
        Convert.ToInt32(customerDataContract.PhoneNum_Cus);
            cust.Email_Cus = customerDataContract.Email_Cus;
            dc.customers.Add(cust);
            dc.SaveChanges();
        }

        //Update/PUT
        public void UpdateCustomer(customer customerDataContract)
        {
            //using (CustomerDataContract Cust = new CustomerDataContract())
            //using (MySQLEntities Cust = new MySQLEntities()) 
            {
                int k = Convert.ToInt32(customerDataContract.Id_Cus);
                customer cust = dc.customers.Where(n => n.Id_Cus == 
           k).Include(a=>a.customerpreference).FirstOrDefault();

                cust.Id_Cus = Convert.ToInt32(customerDataContract.Id_Cus);
                cust.FirstName_Cus = customerDataContract.FirstName_Cus;
                cust.LastName_Cus = customerDataContract.LastName_Cus;
                cust.PhoneNum_Cus = 
              Convert.ToInt32(customerDataContract.PhoneNum_Cus);
                cust.Email_Cus = customerDataContract.Email_Cus;

                dc.SaveChanges();
            }
        }
    }
}
}```



[enter image description here][1]

[enter image description here][2]

[enter image description here][3]


  [1]: https://i.sstatic.net/zlATm.png
  [2]: https://i.sstatic.net/gQju8.png
  [3]: https://i.sstatic.net/6E7vw.png

Answer 1

Yes, you need to explicitly eager load the customer preferences, something like this:

(from a in dc.customers select a).Include(c => c.customerpreference).Distinct();