c# - linq 分组结果需要很长时间

Question

我有以下方法进行一些分组

private List<CatalogVehicle> GroupResult(IEnumerable<VehicleAndQuote> vehiclesAndQuotes)
    {
        var vehicles = vehiclesAndQuotes
            .GroupBy(vehicleAndQuote =>
                new
                {
                    vehicleAndQuote.Vehicle.VehicleMakeName,
                    vehicleAndQuote.Vehicle.VehicleModelTypeName,
                    vehicleAndQuote.Vehicle.VehicleEdition
                })
            .Select(a => new
            {
                vehicle = _mapper.Map<VehicleAndQuote, CatalogVehicle>(a.First()),
                plans = GetLeasingpPlansGroupedByYearlyMileages(a.ToList()) //<== this one is taking ages
            })
            .Select(a =>
            {
                a.vehicle.LeasingPlans = a.plans;
                return a.vehicle;
            });

        return vehicles.ToList();
    }

以及在其中调用的方法；

    private List<LeasingPlan> GetLeasingpPlansGroupedByYearlyMileages(IEnumerable<VehicleAndQuote> vehicleAndQuotes)
    {
        return vehicleAndQuotes.GroupBy(quote => quote.Quote.YearlyMileage)
            .Select(group => _mapper.Map<List<VehicleAndQuote>, LeasingPlan>(group.ToList()))
            .ToList();
    }

最后一种方法需要相当长的时间。 IEnumerable<VehicleAndQuote> vehiclesAndQuotes大约有 30.000 条记录。 是否有任何我没有看到的性能增益？

Answer 1

我正在尝试将您的查询转换为对数据库更友好的版本。

var vehicles = vehiclesAndQuotes
    .GroupBy(vehicleAndQuote =>
                new {
                    vehicleAndQuote.Vehicle.VehicleMakeName,
                    vehicleAndQuote.Vehicle.VehicleModelTypeName,
                    vehicleAndQuote.Vehicle.VehicleEdition
                })
            .Select(a => new {
                // DB friendly
                vehicle = a.First(),
                plans = a.GroupBy(quote => quote.Quote.YearlyMileage)
            })
            .AsEnumerable() // May o may not be needed / passing to LINQ to Objects
            .Select(a => {
                var vehicle = _mapper.Map<VehicleAndQuote, CatalogVehicle>(a.vehicle);
                var plans = a.plans.Select(group => _mapper.Map<IEnumerable<VehicleAndQuote>, LeasingPlan>(group));
                vehicle.LeasingPlans = plans;
                return vehicle;
            });

return vehicles.ToList(); // This should be avoided, specially if you are processing a large collection.

这样你就可以在数据库端进行双重分组。另外，直到最后我才会具体化整个系列。

希望这对您有所帮助!