Question

我的Linq查询花费的时间远远长于SQL等效（Linq约为5-6秒，SQL为50毫秒）。显然翻译中出现了问题，我甚至不知道是什么，但我不知道如何解决它。查询如下：

from data in DbContext.CoacheeData
group data by new { data.User.CompanyId, data.Date } into g
select new GroupedDayData
{
    Id = g.FirstOrDefault().User.CompanyId == null ? "none" : g.FirstOrDefault().User.CompanyId,
    Name = g.FirstOrDefault().User.Company.Name == null ? "none" : g.FirstOrDefault().User.Company.Name,
    Date = g.FirstOrDefault().Date,
    Steps = g.Sum(x => x.Steps),
    Distance = g.Sum(x => x.Distance),
    CaloriesBurned = g.Sum(x => x.CaloriesBurned),
    LightlyActiveMinutes = g.Sum(x => x.LightlyActiveMinutes),
    FairlyActiveMinutes = g.Sum(x => x.FairlyActiveMinutes),
    VeryActiveMinutes = g.Sum(x => x.VeryActiveMinutes),
};

我怀疑在我的group by中使用导航属性User会导致为CoacheeData中的每条记录执行子查询。通过手动加入用户和公司表，我可以将效率提高大约1.5秒，如下所示：

from data in DbContext.CoacheeData
join user in DbContext.Users on data.UserId equals user.Id
join company in DbContext.Companies on user.CompanyId equals company.Id
group data by new { user.CompanyId, company.Name, data.Date } into g
select new GroupedDayData
{
    Id = g.FirstOrDefault().User.CompanyId == null ? "none" : g.FirstOrDefault().User.CompanyId,
    Name = g.FirstOrDefault().User.Company.Name == null ? "none" : g.FirstOrDefault().User.Company.Name,
    Date = g.FirstOrDefault().Date,
    Steps = g.Sum(x => x.Steps),
    Distance = g.Sum(x => x.Distance),
    CaloriesBurned = g.Sum(x => x.CaloriesBurned),
    LightlyActiveMinutes = g.Sum(x => x.LightlyActiveMinutes),
    FairlyActiveMinutes = g.Sum(x => x.FairlyActiveMinutes),
    VeryActiveMinutes = g.Sum(x => x.VeryActiveMinutes),
};

但我的选择看起来仍然相同，也许导航属性导致类似的问题？这看起来很奇怪，因为我之前在选择Linq查询中使用了navigatio属性而没有问题。无论如何，我不确定我的怀疑是否正确，如果是的话，为什么会发生以及如何解决它。

Answer 1

我怀疑要获取 CompanyId ， CompanyName 和 Date 的表达式太复杂，Linq To Sql无法在正确的Sql中翻译它

1）尝试删除选择 CompanyId ， CompanyName 和 Date 的部分以查看它是否变快;

var result =
    from data in DbContext.CoacheeData
    join user in DbContext.Users on data.UserId equals user.Id
    join company in DbContext.Companies on user.CompanyId equals company.Id
    group data by new { CompanyId = user.CompanyId, CompanyName = company.Name, Date = data.Date } into g
    select new GroupedDayData
    {
        Steps = g.Sum(x => x.Steps),
        Distance = g.Sum(x => x.Distance),
        CaloriesBurned = g.Sum(x => x.CaloriesBurned),
        LightlyActiveMinutes = g.Sum(x => x.LightlyActiveMinutes),
        FairlyActiveMinutes = g.Sum(x => x.FairlyActiveMinutes),
        VeryActiveMinutes = g.Sum(x => x.VeryActiveMinutes),
    };

2）如果有帮助，请用g.Key.CompanyId，g.Key.CompanyName和g.Key.Date

之类的内容替换您的表达方式

var result =
    from data in DbContext.CoacheeData
    join user in DbContext.Users on data.UserId equals user.Id
    join company in DbContext.Companies on user.CompanyId equals company.Id
    group data by new { CompanyId = user.CompanyId, CompanyName = company.Name, Date = data.Date } into g
    select new GroupedDayData
    {
        Id = g.Key.CompanyId,
        Name = g.Key.CompanyName,
        Date = g.Key.Date,
        Steps = g.Sum(x => x.Steps),
        Distance = g.Sum(x => x.Distance),
        CaloriesBurned = g.Sum(x => x.CaloriesBurned),
        LightlyActiveMinutes = g.Sum(x => x.LightlyActiveMinutes),
        FairlyActiveMinutes = g.Sum(x => x.FairlyActiveMinutes),
        VeryActiveMinutes = g.Sum(x => x.VeryActiveMinutes),
    };

3）如果这有帮助，请添加null check，你应该得到相同的结果，但速度更快;

var result =
    from data in DbContext.CoacheeData
    join user in DbContext.Users on data.UserId equals user.Id
    join company in DbContext.Companies on user.CompanyId equals company.Id
    group data by new { CompanyId = user.CompanyId, CompanyName = company.Name, Date = data.Date } into g
    select new GroupedDayData
    {
        Id = g.Key.CompanyId ?? "None",
        Name = g.Key.CompanyName ?? "None",
        Date = g.Key.Date,
        Steps = g.Sum(x => x.Steps),
        Distance = g.Sum(x => x.Distance),
        CaloriesBurned = g.Sum(x => x.CaloriesBurned),
        LightlyActiveMinutes = g.Sum(x => x.LightlyActiveMinutes),
        FairlyActiveMinutes = g.Sum(x => x.FairlyActiveMinutes),
        VeryActiveMinutes = g.Sum(x => x.VeryActiveMinutes),
    };

Linq查询的性能问题 - 归咎于导航属性？

1 个答案: