针对强类型数据集的慢速 LINQ 查询

Question

我有一个数据库中大约有 5,000 行。还有许多多对多关系。作为"高级搜索"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，并在应用启动时从 SQL Server 导入所有数据。对数据集执行 LINQ 查询时，查询执行速度非常慢（大约 15 秒）。我认为对内存中数据集执行查询会比 SQL Server 快得多，但事实似乎并非如此。我什至需要在 where 子句中添加更多的连接和"搜索"，所以事情只会变得更糟。

在我正在搜索的字段中，最长的是摘要，数据库中最长的字段小于 2,000 字节，所以我们不谈论要搜索的大量数据。我在这里吠错了树，还是有办法提高此查询的性能？

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

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

预联接要用作搜索索引的数据：

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();

对加载和联接的数据运行搜索：

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，您的示例代码没有理由进行连接，因为条件或答案中没有使用任何连接范围变量，并且无论如何您都会连接每个变量，因此将它们排除在外将是最快的解决方案。

Answer 2

一些想法：

首先，您正在搜索字符串。如果要搜索的内容很多，请考虑维护全文索引以加快搜索速度。

其次，将where条款放在join条款之前。筛选出数据的内容应在 LINQ 语句中尽可能高的位置。它目前正在为每一行加入一堆数据，即使如果 where 子句为 false，也不会使用它。