改进多对多关系的 LINQ 查询

Question

我有一个具有以下架构的数据库：

现在，我正在尝试提取域的所有登录页面，并按与某个组匹配的第一个 UrlFilter 的 FilterType 对它们进行排序。这是我迄今为止提出的 LINQ：

var baseQuery = DbSet.AsNoTracking()
.Where(e => EF.Functions.Contains(EF.Property<string>(e, "Url"), $"\"{searchTerm}*\""))
.Where(e => e.DomainLandingPages.Select(lp => lp.DomainId).Contains(domainId));

var count = baseQuery.Count();
var page = baseQuery
    .Select(e => new
    {
        LandingPage = e,
        UrlFilter = e.LandingPageUrlFilters.FirstOrDefault(f => f.UrlFilter.GroupId == groupId)
    })
    .Select(e => new
    {
        e.LandingPage,
        FilterType = e.UrlFilter == null ? UrlFilterType.NotCovered : e.UrlFilter.UrlFilter.UrlFilterType
    })
    .OrderBy(e => e.FilterType)
    .Skip(10).Take(75).ToList();

现在，虽然这在技术上可行，但执行时间从 10 到 30 秒不等，速度很慢，这对于用例来说还不够好。 LINQ 被转换为以下 SQL：

SELECT [l1].[Id], [l1].[LastUpdated], [l1].[Url], CASE
    WHEN (
        SELECT TOP(1) [l].[LandingPageId]
        FROM [LandingPageUrlFilters] AS [l]
        INNER JOIN [UrlFilters] AS [u] ON [l].[UrlFilterId] = [u].[Id]
        WHERE ([l1].[Id] = [l].[LandingPageId]) AND ([u].[GroupId] = @__groupId_3)) IS NULL THEN 4
    ELSE (
        SELECT TOP(1) [u0].[UrlFilterType]
        FROM [LandingPageUrlFilters] AS [l0]
        INNER JOIN [UrlFilters] AS [u0] ON [l0].[UrlFilterId] = [u0].[Id]
        WHERE ([l1].[Id] = [l0].[LandingPageId]) AND ([u0].[GroupId] = @__groupId_3))
END AS [FilterType]
FROM [LandingPages] AS [l1]
WHERE CONTAINS([l1].[Url], @__Format_1) AND @__domainId_2 IN (
    SELECT [d].[DomainId]
    FROM [DomainLandingPages] AS [d]
    WHERE [l1].[Id] = [d].[LandingPageId]
)

ORDER BY CASE
    WHEN (
        SELECT TOP(1) [l2].[LandingPageId]
        FROM [LandingPageUrlFilters] AS [l2]
        INNER JOIN [UrlFilters] AS [u1] ON [l2].[UrlFilterId] = [u1].[Id]
        WHERE ([l1].[Id] = [l2].[LandingPageId]) AND ([u1].[GroupId] = @__groupId_3)) IS NULL THEN 4
    ELSE (
        SELECT TOP(1) [u2].[UrlFilterType]
        FROM [LandingPageUrlFilters] AS [l3]
        INNER JOIN [UrlFilters] AS [u2] ON [l3].[UrlFilterId] = [u2].[Id]
        WHERE ([l1].[Id] = [l3].[LandingPageId]) AND ([u2].[GroupId] = @__groupId_3))
END
OFFSET @__p_4 ROWS FETCH NEXT @__p_5 ROWS ONLY

现在我的问题是，我怎样才能提高它的执行时间？通过 SQL 或 LINQ

编辑：所以我一直在修改一些原始 SQL，这就是我想出的：

with matched_urls as (
    select l.id, min(f.urlfiltertype) as Filter
    from landingpages l
    join landingpageurlfilters lpf on lpf.landingpageid = l.id
    join urlfilters f on lpf.urlfilterid = f.id
    where f.groupid = @groupId
    and contains(Url, '"barz*"')
    group by l.id
) select l.id, 5 as Filter
from landingpages l
where @domainId in (
    select domainid
    from domainlandingpages dlp
    where  l.id = dlp.landingpageid
) and l.id not in (select id from matched_urls ) and contains(Url, '"barz*"')
union select * from matched_urls
order by Filter
offset 10 rows fetch next 30 rows only

这执行得还不错，将执行时间缩短到约 5 秒。由于这将用于表搜索，但我想进一步降低它。有什么方法可以改进这个 SQL 吗？

Answer 1

看看生成的 SQL 是对的。一般来说，我建议学习 SQL，编写一个执行 SQL 查询，然后按照自己的方式工作（使用存储过程或原始 SQL，或者使用相同的理念设计您的 LINQ 查询。

我怀疑这会更好（未测试）：

var page = (
    from e in baseQuery
    let urlFilter = e.LandingPageUrlFilters.OrderBy(f => f.UrlFilterType).FirstOrDefault(f => f.UrlFilter.GroupId == groupId)
    let filterType = urlFilter == null ? UrlFilterType.NotCovered : e.UrlFilter.UrlFilter.UrlFilterType
    select new 
    {
      LandingPage = e,
      FilterType = filterType
    }
).Skip(10).Take(75).ToList();
    

Answer 2

提高执行时间的方法之一是在 SSMS (SQL Server Management Studio) 中查看执行计划。

查看执行计划后可以设计一些索引，或者如果你没有这方面的经验，你可以看看SSMS是否推荐了一些索引。

接下来尝试创建索引并再次执行查询，看看执行时间是否有所改善。

注意：这只是缩短执行时间的众多可能方法之一...