Linq groupby 和全局计数（不是每组计数）

Question

我有以下疑问：

var query = from incident in _dbContext.VehicleIncidents
                    join vehicle in _dbContext.Vehicles on incident.VehicleId equals vehicle.Id
                    where vehicle.EnterpriseId == enterpriseId
                    group incident by new {incident.ReportDate.Month, incident.ReportDate.Year}
                    into g1
                    orderby g1.Key.Year, g1.Key.Month
                    select new
                    {
                        Month = g1.Key.Month,
                        Year = g1.Key.Year,
                        Cost = g1.Sum(o => o.Cost)
                    };

它返回按月和年聚合的所有事件。但我也需要事件总数。不是每个组的事件，而是总数。所有组的事件的总和。这可以在这个查询中完成，还是只滚动另一个查询以获得全局总数更好？

Answer 1

我相信您可以得到每组的总和，然后将它们相加。类似的东西

var query = from incident in _dbContext.VehicleIncidents
                join vehicle in _dbContext.Vehicles on incident.VehicleId equals vehicle.Id
                where vehicle.EnterpriseId == enterpriseId
                group incident by new {incident.ReportDate.Month, incident.ReportDate.Year}
                into g1
                orderby g1.Key.Year, g1.Key.Month
                select new
                {
                    Month = g1.Key.Month,
                    Year = g1.Key.Year,
                    Cost = g1.Sum(o => o.Cost),
                    Count = g1.Count()
                };
var total = queryResult.SUM(x=>x.count);

我看到的另一种选择是加入子查询，请参阅Join Subquery result in Linq

类似

var subquery = from incident in _dbContext.VehicleIncidents
                    join vehicle in _dbContext.Vehicles on incident.VehicleId equals vehicle.Id
                    where vehicle.EnterpriseId == enterpriseId
                    into g1
                    select new
                    {
                        Total = g1.Count()
                    };

var query = from incident in _dbContext.VehicleIncidents
                    join vehicle in _dbContext.Vehicles on incident.VehicleId equals vehicle.Id
join sub in subquery on 1=1
                    where vehicle.EnterpriseId == enterpriseId
                    group incident by new {incident.ReportDate.Month, incident.ReportDate.Year}
                    into g1
                    orderby g1.Key.Year, g1.Key.Month
                    select new
                    {
                        Month = g1.Key.Month,
                        Year = g1.Key.Year,
                        Cost = g1.Sum(o => o.Cost),
                        Count = sub.total
                    };