Return 查询为空时的默认值

Question

我正在创建一个 linq 查询，我需要在其中 return 年份和汽车价格的最小值和最大值。

Linqpad:

 var result = (from c in Cars           
                 where c.IsShowed == true
                       c.CarCod == carCod                                  
                 group c by c.CarCod into cg
                 select new  {
                 MinPrice = cg.Min(cv => cv.Price) ,
                 MaxPrice = cg.Max(cv => cv.Price),
                 MinYear =  cg.Min(cv => cv.Year),
                 MaxYear =  cg.Max(cv => cv.Year)
                  })
                 .SingleOrDefault();

result.Dump();

如果查询为空，我如何 return 所有属性 MinPrice、MaxPrice、MinYear、MaxYear 的默认值，例如 0。

Answer 1

你应该为此声明中间 Result class:

 var result = (from c in Cars           
               where c.IsShowed && c.CarCod == carCod                                  
               group c by c.CarCod into cg
               select new Result {
                   MinPrice = cg.Min(cv => cv.Price) ,
                   MaxPrice = cg.Max(cv => cv.Price),
                   MinYear =  cg.Min(cv => cv.Year),
                   MaxYear =  cg.Max(cv => cv.Year)
               })
               .SingleOrDefault() ?? new Result();

Return 查询为空时的默认值

Return default value if Query is Empty

entity-framework

linq

linqpad