สอบถามคำสั่ง LINQ to Oracle โดยใช้ Entity Framework จะต้องใช้งาน return เป็น datatable ตาม code ด้านใน

private IEnumerable<DataRow> query_step2;
private void data()
        {
            using (var db = new Entities())
            {
                List<CustomerInfo> ls;             
                ls = (from c in db.CUSTOMER
                      select new CustomerInfo
                      {                        
                          CusID = c.CUSTOMER_ID,
                          Name = c.NAME,
                          BUDGET = c.BUDGET,
                          PAY_DATE = c.PAY_DATE,
                          Age = c.AGE.Value
                      }).ToList();                
                                  
                //เก็บข้อมูลพักไว้ dt
                DataTable dt = ToDataTable<CustomerInfo>(ls);              
                System.Console.WriteLine("ls=" + ls.Count() + " dt=" + dt);
                

                //นำข้อมูล ใน dt มากรองวันที่อีกที   
                var date1 = Convert.ToDateTime("01/12/2561 00:00:00");
                List<CustomerInfo> Sheet1 = dt.AsEnumerable()
                //----------------------ERROR----------------------
                             //.Where(row => Convert.ToDouble(row["BUDGET"]) == Convert.ToDouble(3000000))
                             //.Where(row => Convert.ToDateTime(row["PAY_DATE"]) == Convert.ToDateTime("01/12/2561 13:01:19"))
                             //.Where(row => DateTime.ParseExact(row["PAY_DATE"].ToString(),"dd/MM/YYYY", CultureInfo.InvariantCulture) == new DateTime(2018, 10, 1))           
                             //.Where(row => Convert.ToString(row["CusID"]) == Convert.ToString("C003"))  //string
                //----------------------ERROR----------------------
							 .Select(c => new CustomerInfo
                             {                                                              
                                 CusID = Convert.ToString(c["CusID"]),
                                 Name = Convert.ToString(c["Name"]),
                                 BUDGET = Convert.ToDecimal(c["BUDGET"]),
                                 PAY_DATE = Convert.ToDateTime(c["PAY_DATE"]),
                                 Age = Convert.ToInt32(c["Age"])
                             }).ToList();

               
          DataTable dt_step1 = new DataTable();
          DataColumn CusID = new DataColumn("CusID");
          CusID.DataType = System.Type.GetType("System.String");
          dt_step1.Columns.Add(CusID); //0

          DataColumn Name = new DataColumn("Name");
          Name.DataType = System.Type.GetType("System.String");
          dt_step1.Columns.Add(Name); //1

          DataColumn BUDGET = new DataColumn("BUDGET");
          BUDGET.DataType = System.Type.GetType("System.Double");
          dt_step1.Columns.Add(BUDGET); //3

          DataColumn PAY_DATE = new DataColumn("PAY_DATE");
          PAY_DATE.DataType = System.Type.GetType("System.DateTime");
          dt_step1.Columns.Add(PAY_DATE);//4

          DataColumn Age = new DataColumn("Age");
          Age.DataType = System.Type.GetType("System.Double");
          dt_step1.Columns.Add(Age); //5

          System.Console.WriteLine("foreach (var a in ls)=" + ls.Count());
          //System.Console.WriteLine("foreach (var a in query3)=" + query3.Count());

              foreach (var a in Sheet1)
              {

                  var row = dt_step1.NewRow();
                  row["CusID"] = a.CusID;
                  row["Name"] = a.Name; //1
                  row["BUDGET"] = a.BUDGET;//2
                  row["PAY_DATE"] = Convert.ToDateTime(a.PAY_DATE);//3    
                  System.Console.WriteLine(a.PAY_DATE);
                  row["Age"] = a.Age;//4
                  dt_step1.Rows.Add(row);
              }


          if (dt_step1.Rows.Count > 0)
          {
              System.Console.WriteLine("หลัง foreach dt_step1.Rows.Count=" + dt_step1.Rows.Count);
          }
          
		  //IEnumerable<DataRow> query_step2;                             
          if (comboBox1.Text == "25ปีขึ้นไป")
          {
              query_step2 = from l2 in dt_step1.AsEnumerable()
                            where l2.Field<double>("Age") >= 25
                            select l2;
          }
          else
          {
              double xunit_due = double.Parse(comboBox1.Text);
              query_step2 = from l2 in dt_step1.AsEnumerable()
                            where l2.Field<double>("Age") == xunit_due
                            select l2;
          }

          var rowSources = query_step2.AsEnumerable();
          System.Console.WriteLine("query_step2="+ query_step2.Count() + " rowSources=" + rowSources.Count());
          if (rowSources.Any())
          {
              DataTable dtt = rowSources.CopyToDataTable();
              System.Console.WriteLine("rows.CopyToDataTable()=" + dtt.Rows.Count);
              dt_step1.Clear();
              if (dtt.Rows.Count > 0)
              {
                  System.Console.WriteLine("dt.Rows.Count=" + dtt.Rows.Count);

                  dataGridView1.Columns.Clear();
                  dataGridView1.Rows.Clear();
                  columnx();
                  int row = dtt.Rows.Count - 1;              
                  for (int r = 0; r <= row; r++)
                  {
                      progressBar1.Visible = true;
                      progressBar1.Maximum = row;
                      if (progressBar1.Value <= row - 1)
                      {
                          progressBar1.Value = progressBar1.Value + 1;
                      }
                      dataGridView1.Rows.Add();
                      dataGridView1.Rows[r].Cells[0].Value = dtt.Rows[r].ItemArray[0].ToString();
                      dataGridView1.Rows[r].Cells[1].Value = dtt.Rows[r].ItemArray[1].ToString();
                      dataGridView1.Rows[r].Cells[2].Value = dtt.Rows[r].ItemArray[2].ToString();
                      dataGridView1.Rows[r].Cells[3].Value = dtt.Rows[r].ItemArray[3].ToString();
                      dataGridView1.Rows[r].Cells[4].Value = dtt.Rows[r].ItemArray[4].ToString();

                  }
              }
          }
          else
          {
              System.Console.WriteLine("else");
          }
      }
  }