Question

我有两个表订单，与Customers表相关的汽车。在查询三个表时我得到重复而不是每个客户的单个值。结果查询对我来说有点混乱，你会如何处理这种情况。我正在使用“ViewModel”=模型来索引，创建，编辑，删除客户信息。

 public class ProductVM
    {
        //Products
        public int ProductID { get; set; }
        public string Name { get; set; }
        public Nullable<int> Supplier_ID { get; set; }
        public string Description { get; set; }
        public string Product_Code { get; set; }

        //Specifications
        public int ID { get; set; }
        public string Bullet_Point { get; set; }
        public string Bullet_Point1 { get; set; }
        public Nullable<int> Product_ID { get; set; }


    }

以下是编辑功能。

         [HttpGet]     
public ActionResult Edit(int? id){
List<CustomerVM> CustomerVMlist = new List<CustomerVM>(); // to hold list of Customer and order details

var customerlist =(from Cust in db.Customers
                join Ord in db.Orders on Cust.CustomerID equals Ord.CustomerID
                 join auto in db.AutoMobiles on  Cust.CustomerID equals auto.CustomerID
                 where Cust.CustomerID==1
                 select new { Cust.Name, Cust.Mobileno, Cust.Address, Ord.OrderDate, Ord.OrderPrice,auto.Vehicle_Type}).ToList();

                    foreach (var item in customerlist) {
                        CustomerVM VMOBJ = new CustomerVM();
                        VMOBJ.Name= item.Name;
                        VMOBJ.Mobileno = item.Mobileno;
                        VMOBJ.Address = item.Address;
                        VMOBJ.OrderDate = item.OrderDate;
                        VMOBJ.OrderPrice = item.OrderPrice;
                        VMOBJ.Vehicle_Type = item.Vehicle_Type;
                        CustomerVMlist.Add(VMOBJ);
                    }

                    return View(CustomerVMlist);

                }

Answer 1

您真正希望使用此查询完成什么？您发布的查询有2个内部联接，从客户到订单，从客户到汽车。因此，当客户下达两个订单时，客户将在结果中出现两次。有时，首先在SQL Management Studio中使用常规创建查询，然后将其转换为LINQ。

如果您需要已下订单的所有客户的列表，并希望添加结果中包含的最后一个订单，您可以这样做：

List<CustomerVM> customerList = (
    from cust in db.Customers

    let lastOrder = (
        from ord in db.Orders
        where ord.CustomerID == cust.CustomerID
        orderby ord.OrderDate descending
    ).FirstOrDefault()

    let automobile = (
        from auto in db.Automobiles
        where auto.CustomerID == cust.CustomerID
    ).FirstOrDefault()

    select new CustomerVM {
        Name = Cust.Name,
        Mobileno = Cust.Mobileno,
        Address = Cust.Address,
        OrderDate = lastOrder.OrderDate,
        OrderPrice = lastOrder.OrderPrice,
        Vehicle_Type = automobile.Vehicle_Type
    }
).Tolist();
return View(customerList);

查询时使用LINQ重复三个表以获取Common值。

1 个答案: