找不到类型或名称空间名称“ DataDirEntities”

如何解决找不到类型或名称空间名称“ DataDirEntities”

请帮助我解决此错误消息：

找不到类型或名称空间名称'DataDirEntities'（是 您没有使用参考资料）

这是我的代码：

using FRED.COMMON.BLL;
using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;

namespace FRED.COMMON.DAL
{
    public class ManagevendorOrders
    {
        DataDirEntities objEDM = new DataDirEntities();

        public string CreateUpdateOrder(vendorPurchaSEOrder po )
        {
            string orderNumber = string.Empty;

            try                      
            {
                if (po.OrderID == 0) //Create new order
                {
                    int orderID = objEDM.Orders.Select(x => x.OrderID).Max() + 1;
                    orderNumber = GetorderNumber();

                    var objNewPO = objEDM.Orders.Add(new Order()
                    {
                        OrderID = orderID,ProfCentID = po.ProfCentID,vendorID = po.vendorID,OrderType = po.OrderType,OrderNum = orderNumber,DelivDate = po.DelivDate,Status = po.Status,OrderTime = po.OrderTime,TotalCost = po.TotalCost,OrderDate = po.OrderDate
                    });


                    objEDM.SaveChanges();