C# คำสั่งเช็คข้อมูลในฐานข้อมูลโดยใช้ Entity Framework (ADO.NET Entity Data Model)

public bool CheckData(Customer t)
        {
            bool isSuccess = false;
            using (PetStoreEntities entities = new PetStoreEntities())
            {
                var SelectData = from a in entities.Customers
                                 where a.Name.Contains("")
                                 select a;
                foreach (var a in SelectData)
                {
                    entities.AddToCustomers(t);
                    entities.SaveChanges();
                }
                isSuccess = true;
                return isSuccess;
            }
        }

bool isExist = (from c in entities.Customers
     where c.Name.Equal(t.Name)
     select c).Count > 0 ? true : false;

 #region IService Members


        public bool  GetCustomerById(string customerid)
        {
            using (var entity = new NorthwindEntities())
            {
                List<Customers> cust = (from c in entity.Customers where c.CustomerID == customerid select c).ToList();
                if (cust.Count ==0 )
                {
                    return true;
                }
            }

            return false;
        }

        public bool SaveCustomers(Customers cust)
        {
            using (var entity = new NorthwindEntities())
            {
                try
                {
                    entity.AddToCustomers(cust);
                    entity.SaveChanges();   
                }
                catch (Exception ex)
                {
                    string error = ex.ToString();
                    return true;
                }                            
            }

            return false;
        }

        #endregion

private void Form1_Load(object sender, EventArgs e)
        {
            NortwindWCFService.Customers oCustomer = new WCFUsingEF.NortwindWCFService.Customers();          
            oCustomer.CustomerID = "C001";
            oCustomer.CompanyName = "MyCompanyName";
            oCustomer.ContactName = "MyContactName";
            oCustomer.ContactTitle = "MyContactTitle";
            oCustomer.Address = "MyAddress";
            oCustomer.City = "MyCity";
            oCustomer.PostalCode = "MyPostal";
            oCustomer.Country = "MyCountry";
            oCustomer.Phone = "MyPhone";
            oCustomer.Fax = "MyFax";

            NortwindWCFService.ServiceClient nortwindService = new WCFUsingEF.NortwindWCFService.ServiceClient();

            if (!nortwindService.GetCustomerById(oCustomer.CustomerID))//ไม่มี C001 ใน DB
            {
                try
                {
                    if (nortwindService.SaveCustomers(oCustomer))
                        MessageBox.Show("Save Data Complete");
                    else
                        MessageBox.Show("Cannot Save Data");
                }
                catch (Exception)
                {
                    
                    throw;
                }
            }
            else//มี C001 ใน DB
            {
                MessageBox.Show("CustomerID ซ้ำ !!");
            }
        }

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Serialization;
using System.ServiceModel;
using System.Text;

namespace NorthwindWcfService
{
    // NOTE: If you change the interface name "IService1" here, you must also update the reference to "IService1" in Web.config.
    [ServiceContract]
    public interface IService
    {       
        #region "ส่วนที่ เขียนโค้ด เพิ่ม"
        [OperationContract]
        bool GetCustomerById(string customerid);

        [OperationContract]
        bool SaveCustomers(Customers cust);
        #endregion       
    }

}

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

namespace NorthwindWcfService
{
    // NOTE: If you change the class name "Service1" here, you must also update the reference to "Service1" in Web.config and in the associated .svc file.
    public class Service1 : IService
    {       
        #region IService Members

        public bool  GetCustomerById(string customerid)
        {
            using (var entity = new NorthwindEntities())
            {
                List<Customers> cust = (from c in entity.Customers where c.CustomerID == customerid select c).ToList();
                if (cust.Count ==0 )
                {
                    return false ;
                }
            }

            return true ;
        }

        public bool SaveCustomers(Customers cust)
        {
            using (var entity = new NorthwindEntities())
            {
                try
                {
                    entity.AddToCustomers(cust);
                    entity.SaveChanges();   
                }
                catch (Exception ex)
                {
                    string error = ex.ToString();
                    return false;
                }                            
            }

            return true;
        }

        #endregion
    }
}

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;


namespace WCFUsingEF
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            NortwindWCFService.Customers oCustomer = new WCFUsingEF.NortwindWCFService.Customers();          
            oCustomer.CustomerID = "C001";
            oCustomer.CompanyName = "MyCompanyName";
            oCustomer.ContactName = "MyContactName";
            oCustomer.ContactTitle = "MyContactTitle";
            oCustomer.Address = "MyAddress";
            oCustomer.City = "MyCity";
            oCustomer.PostalCode = "MyPostal";
            oCustomer.Country = "MyCountry";
            oCustomer.Phone = "MyPhone";
            oCustomer.Fax = "MyFax";

            NortwindWCFService.ServiceClient nortwindService = new WCFUsingEF.NortwindWCFService.ServiceClient();

            if (!nortwindService.GetCustomerById(oCustomer.CustomerID))//ไม่มี C001 ใน DB
            {
                try
                {
                    if (nortwindService.SaveCustomers(oCustomer))
                        MessageBox.Show("Save Data Complete");
                    else
                        MessageBox.Show("Cannot Save Data");
                }
                catch (Exception)
                {
                    
                    throw;
                }
            }
            else//มี C001 ใน DB
            {
                MessageBox.Show("CustomerID ซ้ำ !!");
            }
        }
    }
}

//ตรวจสอบค่า ว่าง oCustomer.CompanyName 
            if (oCustomer.CompanyName == string.Empty)
            {
                MessageBox.Show(" กรุณากรอก ข้อมูล Company Name !!");
            }

if (!PetStoreServics.GetCustomerById(oCustomer.Name))
            {
                try
                {
                    if (oCustomer.Name == string.Empty)
                    {
                        MessageBox.Show(" กรุณากรอกข้อมูลด้วยค่ะ!!");
                    }

                    else if
                        (PetStoreServics.SaveCustomers(oCustomer))
                    {
                        MessageBox.Show("Save Data Complete");
                    }  
                }
                    
                catch (Exception)
                {

                    throw;
                }
            }
            else
            {
                MessageBox.Show("ชื่อนี้มีอยู่ในระบบแล้ว");
            }
            showdata();
        }