针对强类型数据集的慢速 LINQ 查询

Question

我有一个包含大约 5,000 行的数据库。还有许多多对多关系。作为 "advanced search" 查询的一部分，我需要跨表进行自由文本搜索。

我创建了一个强类型数据集，并在应用程序启动时从 SQL 服务器导入所有数据。在对数据集执行 LINQ 查询时，查询执行得非常慢（大约 15 秒）。我认为针对内存数据集执行查询会比 SQL 服务器快得多，但事实并非如此。我什至需要在 where 子句中添加更多连接和 "searches"，所以事情只会变得更糟。

在我搜索的字段中，最长的是 Summary，数据库中最长的字段不到 2,000 字节，所以我们不是在谈论要搜索的大量数据。我是不是找错树了，还是有办法提高这个查询的性能？

代码如下：

var results = from e in _data.ds.Employee
      join es in _data.ds.EmployeeSkill on e.EmployeeId equals es.EmployeeId into esGroup from esItem in esGroup.DefaultIfEmpty()
      join s in _data.ds.Skill on esItem?.SkillId equals s.SkillId into sGroup from skillItem in sGroup.DefaultIfEmpty()
      join er in _data.ds.EmployeeRole on e.EmployeeId equals er.EmployeeId into erGroup from erItem in erGroup.DefaultIfEmpty()
      join r in _data.ds.Role on erItem?.RoleId equals r.RoleId into rGroup from rItem in rGroup.DefaultIfEmpty()
      join et in _data.ds.EmployeeTechnology on e.EmployeeId equals et.EmployeeId into etGroup from etItem in etGroup.DefaultIfEmpty()
      join t in _data.ds.Technology on etItem?.TechnologyId equals t.TechnologyId into tGroup from tItem in etGroup.DefaultIfEmpty()
      where
        e.FirstName.IndexOf(searchTerm, StringComparison.OrdinalIgnoreCase) >= 0 ||
        e.LastName.IndexOf(searchTerm, StringComparison.OrdinalIgnoreCase) >= 0 ||
        e.RMMarket.IndexOf(searchTerm, StringComparison.OrdinalIgnoreCase) >= 0 ||
        !e.IsSummaryNull() && e.Summary.IndexOf(searchTerm, StringComparison.OrdinalIgnoreCase) >= 0
      select new SearchResult
      {
          EmployeeId = e.EmployeeId,
          Name = e.FirstName + " " + e.LastName,
          Title = e.Title,
          ImageUrl = e.IsImageUrlNull() ? string.Empty : e.ImageUrl,
          Market = e.RMMarket,
          Group = e.Group,
          Summary = e.IsSummaryNull() ? string.Empty : e.Summary.Substring(1, e.Summary.Length < summaryLength ? e.Summary.Length - 1 : summaryLength),
          AdUserName = e.AdUserName
      };

Answer 1

一些想法：

首先，您要搜索字符串。如果要搜索的东西很多，可以考虑维护一个全文索引来加快速度。

其次，将where子句放在join子句之前。过滤掉数据的东西在 LINQ 语句中应该尽可能高。它目前正在为每一行加入一堆数据，即使在 where 子句为 false 时也不会使用它。

Answer 2

假设您仍然加载到 DataSets 而不是对象列表（没有足够的信息来翻译该部分），这是我的建议：

预加入数据以用作您的搜索索引：

var searchBase = (from e in _data.ds.Employee
             join es in _data.ds.EmployeeSkill on e.EmployeeId equals es.EmployeeId into esGroup
             from esItem in esGroup.DefaultIfEmpty()
             join s in _data.ds.Skill on esItem?.SkillId equals s.SkillId into sGroup
             from skillItem in sGroup.DefaultIfEmpty()
             join er in _data.ds.EmployeeRole on e.EmployeeId equals er.EmployeeId into erGroup
             from erItem in erGroup.DefaultIfEmpty()
             join r in _data.ds.Role on erItem?.RoleId equals r.RoleId into rGroup
             from rItem in rGroup.DefaultIfEmpty()
             join et in _data.ds.EmployeeTechnology on e.EmployeeId equals et.EmployeeId into etGroup
             from etItem in etGroup.DefaultIfEmpty()
             join t in _data.ds.Technology on etItem?.TechnologyId equals t.TechnologyId into tGroup
             from tItem in etGroup.DefaultIfEmpty()
             select new {
                e.FirstName, e.LastName, e.RMMarket, e.Summary,
                e.EmployeeID, e.Title, e.ImageUrl, e.Group, e.AdUserName
             }).ToList();

运行对加载和连接的数据进行搜索：

var results = from e in searchBase
          where
                e.FirstName.IndexOf(searchTerm, StringComparison.OrdinalIgnoreCase) >= 0 ||
                e.LastName.IndexOf(searchTerm, StringComparison.OrdinalIgnoreCase) >= 0 ||
                e.RMMarket.IndexOf(searchTerm, StringComparison.OrdinalIgnoreCase) >= 0 ||
                !e.IsSummaryNull() && e.Summary.IndexOf(searchTerm, StringComparison.OrdinalIgnoreCase) >= 0
          select new SearchResult {
              EmployeeId = e.EmployeeId,
              Name = e.FirstName + " " + e.LastName,
              Title = e.Title,
              ImageUrl = e.IsImageUrlNull() ? string.Empty : e.ImageUrl,
              Market = e.RMMarket,
              Group = e.Group,
              Summary = e.IsSummaryNull() ? string.Empty : e.Summary.Substring(1, e.Summary.Length < summaryLength ? e.Summary.Length - 1 : summaryLength),
              AdUserName = e.AdUserName
          };

顺便说一句，您的示例代码显示没有理由进行连接，因为连接范围变量的 none 正在条件或答案中使用，而且您无论如何都要连接每个变量，所以将它们排除在外将是最快的解决方案。

针对强类型数据集的慢速 LINQ 查询

Slow LINQ query against strongly typed Dataset

c#

sql-server

linq

search

strongly-typed-dataset