Linq，在匿名类型中使用“变量”

Question

我正在努力完成这样的事情，

var data = from p in db.Projects
                   select new
                   {
                       Cost = p.CostReports.FirstOrDefault().Charged,
                       Tax = Cost * 0.25
                   };

换句话说，我想将Cost用作变量。可能吗？如果是这样，怎么样？

我的代码只是一个例子，我正在研究的项目有点复杂。

编辑：

我希望这是我正在尝试做的更好的例子，

var data = (from p in db.Projects
                    select new
                    {
                        Name = p.ProjectName,
                        Customer = p.CustomerID,
                        Cost = p.Cost
                    }).GroupBy(p => p.Customer)
                   .Select(g => new
                   {
                       Something = g.Where(p => p.Customer == g.Key).Sum(p => p.Cost),
                       SomethingElse = Something * 0.25
                   });

Answer 1

在查询中使用let关键字。

var data = from p in db.Projects 
           let cost = p.CostReports.FirstOrDefault().Charged
           select new 
           { 
              Cost = cost,
              Tax = cost * 0.25 
           }; 

修改

关于您的更新并禁止其他信息，我可能仍然想通过重写您的查询结构来使用let。

var data = from g in db.Projects.Select(p => 
                new
                {
                    Name = p.ProjectName,
                    Customer = p.CustomerID,
                    Cost = p.Cost
                }
            ).GroupBy(p => p.Customer)
            let something = g.Sum(p => p.Cost)
            select new
            {
                Something = something,
                SomethingElse = something * 0.25
            };

在这种情况下，from g in ...引用分组数据，允许您对此数据使用查询表达式语法，包括let。

Answer 2

var data = from p in db.Projects
           let cost = p.CostReports.FirstOrDefault().Charged
           select new
           {
               Cost = cost,
               Tax = cost * 0.25
           };

Answer 3

您至少可以将选择链在一起并将您的匿名类型存储为中间结果：

var data = (from p in db.Projects
               select new
               {
                   Cost = p.CostReports.FirstOrDefault().Charged,
                   Tax = Cost * 0.25
               })
           .select(anon => new { Cost = anon.Cost, Tax = anon.Cost * 0.25 });