有没有办法减少数据库的点击次数

Question

我是 C#、ASP.NET MVC 和 SQL Server 的新手，但我已经让这段代码工作了

DateTime startDate = DateTime.Parse(start);
DateTime endDate = DateTime.Parse(end);

ViewData["TotalDuringPeriod"] = db.AlcoholForms.Count(x => x.CreatedDate >= startDate && x.CreatedDate <= endDate);
ViewData["TotalUniqueClientsDuringPeriod"] = db.AlcoholForms.Where(x => x.CreatedDate >= startDate && x.CreatedDate <= endDate).Select(x => x.ClientId).Distinct().Count();
ViewData["TotalGateNew"] = db.AlcoholForms.Count(x => x.ReferredTo == "Gate" && x.Reengagement == false && (x.CreatedDate >= startDate && x.CreatedDate <= endDate));
ViewData["TotalGateReengagment"] = db.AlcoholForms.Count(x => x.ReferredTo == "Gate" && x.Reengagement && (x.CreatedDate >= startDate && x.CreatedDate <= endDate));
ViewData["TotalSwitchNew"] = db.AlcoholForms.Count(x => x.ReferredTo == "Switch" && x.Reengagement == false && (x.CreatedDate >= startDate && x.CreatedDate <= endDate));
ViewData["TotalSwitchReengagement"] = db.AlcoholForms.Count(x => x.ReferredTo == "Switch" && x.Reengagement && (x.CreatedDate >= startDate && x.CreatedDate <= endDate));

List<ReportAlcoholReferals> reportData = db.AlcoholForms.Where(x => x.Referral && (x.CreatedDate >= startDate && x.CreatedDate <= endDate)).Select(x => new ReportAlcoholReferals()
            {
                FirstName = x.Client.FirstName,
                LastName = x.Client.LastName,
                Date = x.CreatedDate,                 
                ClientId = x.ClientId,
                AlcoholForm = x
            }).OrderBy(x => x.AlcoholForm.ReferredTo).ToList();
            return View(reportData);

现在它可以工作了，但我要访问数据库 7 次？有没有更好的方法来做到这一点？ 有多大的性能问题

Answer 1

这就是我将如何处理这个问题，只是在不经常访问数据库的情况下。您可能还可以进行其他改进，但这不是您想要的。

DateTime startDate = DateTime.Parse(start);
DateTime endDate = DateTime.Parse(end);
List<AlcoholForms> formsList = db.AlcoholForms.Where(x => x.CreatedDate >= startDate && x.CreatedDate <= endDate).ToList();

ViewData["TotalDuringPeriod"] = formsList.Count();
ViewData["TotalUniqueClientsDuringPeriod"] = formsList.Select(x => x.ClientId).Distinct().Count();
ViewData["TotalGateNew"] = formsList.Count(x => x.ReferredTo == "Gate" && x.Reengagement == false);
ViewData["TotalGateReengagment"] = formsList.Count(x => x.ReferredTo == "Gate" && x.Reengagement);
ViewData["TotalSwitchNew"] = formsList.Count(x => x.ReferredTo == "Switch" && x.Reengagement == false);
ViewData["TotalSwitchReengagement"] = formsList.Count(x => x.ReferredTo == "Switch" && x.Reengagement);
List<ReportAlcoholReferals> reportData = formsList.Where(x => x.Referral).Select(x => new ReportAlcoholReferals()
{
    FirstName = x.Client.FirstName,
    LastName = x.Client.LastName,
    Date = x.CreatedDate,                 
    ClientId = x.ClientId,
    AlcoholForm = x
}).OrderBy(x => x.AlcoholForm.ReferredTo).ToList();

return View(reportData);

formsList 的列表声明意味着数据库将被查询一次并将结果存储在 List 对象中。从那里，您可以继续使用 LINQ 来分解您的数据。

Answer 2

您的第三个到第六个查询可以从四个不同的计数转换为一个分组来捕获每个组的计数：

var lookup = db.AlcoholForms.Where(x => x.CreatedDate >= startDate && 
        x.CreatedDate <= endDate)
    .GroupBy(x => new { x.ReferredTo, x.Reengagement },
        (key, items) => new{key, count = items.Count()})
    .ToDictionary(group => group.key, group => group.count);

ViewData["TotalGateNew"] = lookup[
    new { ReferredTo = "Gate", Reengagement = false }];
ViewData["TotalGateReengagment"] = lookup[
    new { ReferredTo = "Gate", Reengagement = true }];
ViewData["TotalSwitchNew"] = lookup[
    new { ReferredTo = "Switch", Reengagement = false }];
ViewData["TotalSwitchReengagement"] = lookup[
    new { ReferredTo = "Switch", Reengagement = true }];

Answer 3

往返次数不一定是坏事。你有没有分析过这七首热门歌曲，看看它们是否真的花时间？我的猜测是他们不是，这意味着你没事（除非这将在一个非常高容量的站点上运行）。

另一种方法是编写一个 T-SQL 存储过程，一次性返回您需要的所有值。然后，您可以将结果捕获为一个对象，或者只是一个整数列表，或其他任何内容。