Question

我在将SQL查询转换为Linq（尤其是在“分组依据”部分中）时遇到问题。

SQL：

SELECT 
year(ord.OrderDT) as ODate1,
month(ord.OrderDT) as ODate2,
cus.Company as Company,
sum(ord.InvoiceTotal) as TotalRate,
count(ord.InvoiceTotal) as CountOrd
  FROM [dbo].[Customer] as cus
  join [dbo].[Order] as ord on cus.CustomerID=ord.CustomerID
  group by year(ord.OrderDT), month(ord.OrderDT), Company
  order by ODate1 desc, ODate2 desc, Company

我尝试过：

var result = (from cus in dbf.Customer
                      join ord in dbf.Order on cus.CustomerId equals ord.CustomerId
                      select new {
                          Year=ord.OrderDt.Year,
                          Month=ord.OrderDt.Month,
                          Company=cus.Company,
                          Rate=ord.InvoiceTotal
     
                      } into t1
                      group t1 by new {t1.Year, t1.Month,t1.Company} into t2
                      select new
                      {
                          Year=t2.FirstOrDefault().Year,
                          Month=t2.FirstOrDefault().Month,
                          Customer=t2.FirstOrDefault().Company,
                          TotalRate=t2.Sum(c=>c.Rate)
                      }         
                      ).Take(10).ToList();

但是我收到错误消息：“。FirstOrDefault（）'无法翻译。要么以可以翻译的形式重写查询”。如果我尝试摆脱“ FirstOrDefault”，那么我就没有t2的智能感知

实体：

 public Customer()
        { 
        public int CustomerId { get; set; }
        public string Company { get; set; }
}

 public Order()
        { 
        public int OrderNo { get; set; }
        public int CustomerId { get; set; }
        public DateTime OrderDT { get; set; }
        public decimal InvoiceTotal { get; set; }
}

Answer 1

尝试下一条选择语句：

 select new
 {
     Year=t2.Key.Year,
     Month=t2.Key.Month,
     Customer=t2.Key.Company,
     TotalRate=t2.Sum(c=>c.Rate)
 }

Answer 2

最终查询如下。

    var result = (from cus in dbf.Customer
                  join ord in dbf.Order on cus.CustomerId equals ord.CustomerId
                  select new {
                      Year=ord.OrderDt.Year,
                      Month=ord.OrderDt.Month,
                      Company=cus.Company,
                      Rate=ord.InvoiceTotal
 
                  } into t1
                  group t1 by new {t1.Year, t1.Month,t1.Company} into t2
                  orderby t2.Key.Year descending, t2.Key.Month descending,t2.Key.Company ascending
                  
                  select new
                  {
                      Year=t2.Key.Year,
                      Month=t2.Key.Month,
                      Customer=t2.Key.Company,
                      TotalRate=t2.Sum(c=>c.Rate),
                      Count=t2.Count()
                  }         
                  ).ToList();

将SQL查询翻译成Linq

2 个答案: