c# - 加速 40,000 行的 linq 查询

Question

在我的服务中，首先我生成 40,000 种可能的母国和东道国组合，如下所示(clientLocations 包含 200 条记录，因此 200 x 200 是 40,000):

foreach (var homeLocation in clientLocations)
{
    foreach (var hostLocation in clientLocations)
    {
        allLocationCombinations.Add(new AirShipmentRate
        {
            HomeCountryId = homeLocation.CountryId,
            HomeCountry = homeLocation.CountryName,
            HostCountryId = hostLocation.CountryId,
            HostCountry = hostLocation.CountryName,
            HomeLocationId = homeLocation.LocationId,
            HomeLocation = homeLocation.LocationName,
            HostLocationId = hostLocation.LocationId,
            HostLocation = hostLocation.LocationName,
        });
    }
}

然后，我运行以下查询来查找上述位置的现有费率，但也包括空的缺失费率；生成包含 40,000 行的完整记录集。

var allLocationRates = (from l in allLocationCombinations
                        join r in Db.PaymentRates_AirShipment
                            on new { home = l.HomeLocationId, host = l.HostLocationId }
                            equals new { home = r.HomeLocationId, host = (Guid?)r.HostLocationId }
                        into matches
                        from rate in matches.DefaultIfEmpty(new PaymentRates_AirShipment
                        {
                            Id = Guid.NewGuid()
                        })
                        select new AirShipmentRate
                        {
                            Id = rate.Id,
                            HomeCountry = l.HomeCountry,
                            HomeCountryId = l.HomeCountryId,
                            HomeLocation = l.HomeLocation,
                            HomeLocationId = l.HomeLocationId,
                            HostCountry = l.HostCountry,
                            HostCountryId = l.HostCountryId,
                            HostLocation = l.HostLocation,
                            HostLocationId = l.HostLocationId,
                            AssigneeAirShipmentPlusInsurance = rate.AssigneeAirShipmentPlusInsurance,
                            DependentAirShipmentPlusInsurance = rate.DependentAirShipmentPlusInsurance,
                            SmallContainerPlusInsurance = rate.SmallContainerPlusInsurance,
                            LargeContainerPlusInsurance = rate.LargeContainerPlusInsurance,
                            CurrencyId = rate.RateCurrencyId
                        });

我尝试过使用 .AsEnumerable() 和 .AsNoTracking()，这大大加快了速度。 以下代码使我的查询时间缩短了几秒钟:

var allLocationRates = (from l in allLocationCombinations.AsEnumerable()
                        join r in Db.PaymentRates_AirShipment.AsNoTracking()

但是，我想知道:如何才能加快速度？

编辑:无法在 linq 中复制 foreach 功能。

allLocationCombinations = (from homeLocation in clientLocations
                            from hostLocation in clientLocations
                            select new AirShipmentRate
                            {
                                HomeCountryId = homeLocation.CountryId,
                                HomeCountry = homeLocation.CountryName,
                                HostCountryId = hostLocation.CountryId,
                                HostCountry = hostLocation.CountryName,
                                HomeLocationId = homeLocation.LocationId,
                                HomeLocation = homeLocation.LocationName,
                                HostLocationId = hostLocation.LocationId,
                                HostLocation = hostLocation.LocationName
                            });

我在 from hostLocation in clientLocations 上收到错误，提示“无法将 IEnumerable 类型转换为 Generic.List。”

Answer 1

查询数据库最快的方法是使用数据库引擎本身的功能。

虽然 Linq 是一种非常棒的技术，但它仍然从 Linq 查询中生成一个 select 语句，并针对数据库运行此查询。

最好的选择是创建数据库 View 或存储过程。

View 和存储过程可以轻松集成到 Linq 中。

Material Views(在 MS SQL 中)可以进一步加快执行速度，而缺失索引是迄今为止加速数据库查询的最有效工具。