LINQ C# 中的条件计数分组依据

Posted 2023-02-16

【中文标题】LINQ C# 中的条件计数分组依据

【英文标题】：Conditional count group by in LINQ C#

【发布时间】：2021-09-02 00:57:44

【问题描述】：

我有一个代码可以计算 7 天内的记录：

  var r=  (from t in _context.Services
         where
            t.ServiceDate.Date >= FirstDay.Date &&
            t.ServiceDate.Date <= SeventhDay.Date 
         group t by new  t.ServiceDate.Year, t.ServiceDate.Month, t.ServiceDate.Day, t.Solution  into g
         select new DateAndCoint 
          
             date = new DateTime(g.Key.Year, g.Key.Month, g.Key.Day),
             count = g.Count() )
         .ToList();

它工作正常，但我有一个名为 Solution (bool) 的字段，它指示记录是否完​​成

所以我喜欢计算完成的记录（哪个解决方案是正确的）除了上述计数？ 我试过了：

countDone = g.Where(x=>x.Solution).Count()

但它给了我一个运行时错误

InvalidOperationException: The LINQ expression '(GroupByShaperExpression:
KeySelector: new 
Year = (DATEPART((year), (s.ServiceDate))),
Month = (DATEPART((month), (s.ServiceDate))),
Day = (DATEPART((day), (s.ServiceDate))),
Solution = (s.Solution)
,
ElementSelector:(EntityShaperExpression:
EntityType: Service
ValueBufferExpression:
(ProjectionBindingExpression: EmptyProjectionMember)
IsNullable: False
)
)
.Where(x => x.Solution)' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync().

---

有什么办法吗？

【参考方案1】：

EF Core 5.x 支持此类Count。由于您的查询不起作用，您可以将Count 模拟为Sum

 var query = 
    from t in _context.Services
    where
        t.ServiceDate.Date >= FirstDay.Date &&
        t.ServiceDate.Date <= SeventhDay.Date 
    group t by new  t.ServiceDate.Year, t.ServiceDate.Month, t.ServiceDate.Day, t.Solution  into g
    select new DateAndCoint 
     
        date = new DateTime(g.Key.Year, g.Key.Month, g.Key.Day),
        count = g.Count(),
        countDone = g.Sum(x => x.Solution ? 1 : 0) 
    ;