我想了解爲什麼加入我的情況比使用導航屬性的語句更快。我有兩個疑問。實體框架性能連接與導航屬性
先用導航屬性:
var result = (from users in context.MetricBloodPreasure
orderby users.User.LastName, users.User.FirstName
select new
{
UserName = users.User.LastName + ", " + users.User.FirstName,
Date = users.DateOfValue,
}).ToList();
Generatet SQL:
SELECT
[Project1].[C1] AS [C1],
[Project1].[C2] AS [C2],
[Project1].[DateOfValue] AS [DateOfValue]
FROM (SELECT
[Extent1].[DateOfValue] AS [DateOfValue],
[Extent2].[FirstName] AS [FirstName],
[Extent2].[LastName] AS [LastName],
1 AS [C1],
CASE WHEN ([Extent2].[LastName] IS NULL) THEN N'' ELSE [Extent2].[LastName] END + N', ' + CASE WHEN ([Extent2].[FirstName] IS NULL) THEN N'' ELSE [Extent2].[FirstName] END AS [C2]
FROM [dbo].[MetricBloodPreasure] AS [Extent1]
INNER JOIN [dbo].[User] AS [Extent2] ON [Extent1].[UserId] = [Extent2].[Id]
) AS [Project1]
ORDER BY [Project1].[LastName] ASC, [Project1].[FirstName] ASC
第二位加盟:
var result1 = (from u in context.User
orderby u.LastName, u.FirstName
join us in context.MetricBloodPreasure
on u.Id equals us.UserId into users
from s in users
select new
{
UserName = s.User.LastName + ", " + s.User.FirstName,
Date = s.DateOfValue,
}).ToList();
生成的SQL:
SELECT
1 AS [C1],
CASE WHEN ([Extent1].[LastName] IS NULL) THEN N'' ELSE [Extent1].[LastName] END + N', ' + CASE WHEN ([Extent1].[FirstName] IS NULL) THEN N'' ELSE [Extent1].[FirstName] END AS [C2],
[Extent2].[DateOfValue] AS [DateOfValue]
FROM [dbo].[User] AS [Extent1]
INNER JOIN [dbo].[MetricBloodPreasure] AS [Extent2] ON ([Extent1].[Id] = [Extent2].[UserId]) AND ([Extent2].[UserId] = [Extent1].[Id])
在運行第一個查詢之前,請撥打var user = context.User.FirstOrDefault();
,因爲我認爲與數據庫的開放連接需要一些時間。
結果: 導航屬性查詢:00:00:00.6719646 加入查詢:00:00:00.4941169
看結果似乎LINQ查詢在使用連接,而不是導航性能更快。這是真的還是我做錯了什麼?
您還需要在查詢之間清除數據庫中的緩存,以便在調用ToList()時獲得正確的結果。將查詢結構從實現中分離出來並進行基準測試。 –
OrderBy在第二個查詢中似乎沒有考慮到。這可能是導致差異的原因,你可以嘗試'...從用戶的命令u.LastName,u.FirstName ...' – jbl