求教Include 方法在 linq to sql / entity framwork使用方法

Customer 类里有

        public int? CityId { get; set; }



        public virtual City City { get; set; }

代码如下，Customers表里有CityID， 然后 “Include("Cooperations").Include("Staff").Include("City")” 后
public virtual City City { get; set; } 这个属性始终没有赋值，就是Include("City") 没有被执行。

除非 我在第一行写成 “var query = from a in dbContext.Customers.Include("Cooperations").Include("Staff").Include("City").ToList()”

但是这样运行时又报错。 求指教。。。。。。。。。

var query = from a in dbContext.Customers.Include("Cooperations").Include("Staff").Include("City")

                            join b in dbContext.Business

                            on new { Cus = a.ID, Stf = a.StaffID } equals new { Cus = b.CustomerID == null ? 0 : b.CustomerID.Value, Stf = b.StaffID } into t

                            join c in dbContext.Provinces on (a.CityId == null ? 0 : a.City.ProvinceID) equals c.ID into x



                            where staffids.Contains(a.StaffID == null ? -1 : a.StaffID.Value)

                            select new BusinessVM

                            {

                                Customer = a,

                                Business = t.Where(p => (p.CreateTime > parm.startdate.Value && p.CreateTime < parm.enddate.Value)),

                                Provienc = "江南"

                            };

                return query.OrderByDescending(u => u.Customer.ID).Skip(itemIndex).Take(pageSize).ToList();