Question

我有一个大约有5,000行的数据库。还有许多多对多的关系。作为“高级搜索”查询的一部分，我需要跨表格进行自由文本搜索。

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。在对数据集执行LINQ查询时，查询执行速度非常慢（大约15秒）。我认为针对内存数据集执行查询会比SQL Server快得多，但似乎并非如此。我甚至需要在where子句中添加更多连接和“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Summary，而数据库中最长的是小于2,000字节，所以我们不是在讨论要搜索的大量数据。我在这里咆哮错误的树，还是有办法改善这个查询的性能？

以下是代码：

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，您正在搜索字符串。如果要搜索很多内容，请考虑维护全文索引以加快速度。

其次，将where子句放在join子句之前。过滤掉数据的东西应尽可能高在LINQ语句中。它目前正在为每一行加入一堆数据，即使在where子句为假的情况下也不会使用它。

Answer 2

假设您仍然加载到DataSet而不是对象列表（没有足够的信息来翻译该部分），我建议这样做：

预先加入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();

针对加载和加入的数据运行搜索：

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，你的示例代码没有显示连接的原因，因为没有任何连接范围变量在条件或答案中使用，并且你仍然无论如何都要加入每个连接，所以将它们排除在外是最快的解决方案。

针对强类型数据集的慢LINQ查询

2 个答案: