Question

主要问题是当我在SQL Management studio中执行某个查询时，大约需要2秒钟。当通过实体框架执行并且我使用分析器查看它时，查询需要260秒。结果只有72行1整数。此查询是根据用户定义的过滤器构建的。

有没有人有任何建议可能有什么问题？我在分析器中可以看到的sqlquery如下：

SELECT [Distinct1].[PersonID] AS [PersonID]
FROM   (SELECT DISTINCT [Extent1].[PersonID] AS [PersonID]
         FROM   (SELECT [PersonViewWithExtraInfo].[PersonID]           AS         [PersonID],
                   [PersonViewWithExtraInfo].[DateTime]             AS [DateTime],
                   [PersonViewWithExtraInfo].[ExtraInfo1]         AS [ExtraInfo1],
                   [PersonViewWithExtraInfo].[ExtraInfo2]           AS [ExtraInfo2],
                   [PersonViewWithExtraInfo].[ExtraInfo3]               AS [ExtraInfo3],
                   [PersonViewWithExtraInfo].[ExtraInfo4] AS [ExtraInfo4]
            FROM   [core].[PersonViewWithExtraInfo].AS [PersonViewWithExtraInfo].AS [Extent1]
           LEFT OUTER JOIN [core].[Persons] AS [Extent2]
             ON [Extent1].[PersonID] = [Extent2].[PersonID]
    WHERE  ([Extent1].[ExtraInfo4] = 1)
           AND(([Extent2].[FirstName] = 'Steven' /* @p__linq__0 */)
                 OR (([Extent2].[FirstName] IS NULL)
                     AND ('Steven' /* @p__linq__0 */ IS NULL))
                 OR ([Extent2].[FirstName] = 'Steffi' /* @p__linq__1 */)
                 OR (([Extent2].[FirstName] IS NULL)
                     AND ('Steffi' /* @p__linq__1 */ IS NULL))
                 OR ([Extent2].[FirstName] = 'Evy' /* @p__linq__2 */)
                 OR (([Extent2].[FirstName] IS NULL)
                     AND ('Evy' /* @p__linq__2 */ IS NULL)))
           AND ([Extent1].[DateTime] >= '2014-06-01T00:00:00' /* @p__linq__3 */)
           AND ([Extent1].[DateTime] <= '2015-05-31T00:00:00' /* @p__linq__4 */)) AS [Distinct1]

我构建了我的where子句来比较像这样的字符串：

public static Expression<Func<string, bool>> ConvertToExpression(this FilterComparer comparer, string compareValue)
  {
     switch (comparer)
     {
        case FilterComparer.IsEqualTo:
           return x => x == compareValue;
...

编辑：我发现了问题所在。当我从sqlprofiler中获取查询时，查询被exec sp_executesql包围，当我在管理工作室中粘贴时，查询与EF一样长。因此，当我在此查询中删除空检查时，延迟消失了。当他说“每个where子句有太多表达式”时，我应该听EF编辑器。唯一的问题是实体框架添加了空检查。我该如何防止这种情况？

编辑：这是我从Linq Insight获得的linq查询。

(from x in     ((ObjectQuery<PersonViewWithExtraInfo>)PersonViewWithExtraInfo).MergeAs(0)
where x.ExtraInfo4 && (((False || (True && (x.Person.FirstName     == compareValue))) || (True && (x.Person.FirstName == compareValue))) || (True     && (x.Person.FirstName == compareValue)))
where (x.DateTime >= startDate.Date) && (x.DateTime <= endDate.Date)
select x.PersonID).Distinct()

真实和假的存在是因为查询是根据用户定义的过滤器动态构建的。

Answer 1

所以问题是EF在查询中添加了空检查，这使得where子句变大了。通过设置

Configuration.UseDatabaseNullSemantics = true;

在DbContext上

问题解决了！

实体框架中的查询需要比直接sql

1 个答案: