[英]C# Recursive Query
我正在做一個項目,我使用 C# 填充來自多個來源的單個 MSSQL 表。
該表包含鏈接重定向信息(下面的示例結構)。
RequestedURL, RedirectedURL
www.123.com, www.123.com/123
www.123.com/123, www.123.com/1234/link.asp
www.123.com/1234/link.asp, www.123.com/12345/link.asp
我對 C# 非常陌生,需要通過每個重定向 URL 向 go 編寫某種遞歸查詢,如果它在請求的 URL 中,然后找到關聯的重定向 URL。 某些 URL 可能有多個重定向。
由於您的 SQL 服務器數據庫中有這些數據,因此一種可能的方法是CTE 與 recursion 。 這個解釋一開始看起來有點混亂,但我認為如果你向下滾動到這個例子,就會很清楚如何做到這一點。
此處不重復整個解釋,這是此類查詢的示例:
USE AdventureWorks2008R2;
GO
WITH DirectReports (ManagerID, EmployeeID, Title, DeptID, Level)
AS
(
-- Anchor member definition
SELECT e.ManagerID, e.EmployeeID, e.Title, edh.DepartmentID,
0 AS Level
FROM dbo.MyEmployees AS e
INNER JOIN HumanResources.EmployeeDepartmentHistory AS edh
ON e.EmployeeID = edh.BusinessEntityID AND edh.EndDate IS NULL
WHERE ManagerID IS NULL
UNION ALL
-- Recursive member definition
SELECT e.ManagerID, e.EmployeeID, e.Title, edh.DepartmentID,
Level + 1
FROM dbo.MyEmployees AS e
INNER JOIN HumanResources.EmployeeDepartmentHistory AS edh
ON e.EmployeeID = edh.BusinessEntityID AND edh.EndDate IS NULL
INNER JOIN DirectReports AS d
ON e.ManagerID = d.EmployeeID
)
-- Statement that executes the CTE
SELECT ManagerID, EmployeeID, Title, DeptID, Level
FROM DirectReports
INNER JOIN HumanResources.Department AS dp
ON DirectReports.DeptID = dp.DepartmentID
WHERE dp.GroupName = N'Sales and Marketing' OR Level = 0;
GO
您可以創建一個字典,其中RequestedUrl
作為鍵, RedirectedUrl
作為值。 所以一旦你找到了requestedUrl,你就可以找到它的redirectedURL,如果redirectedURL 有redirectedURL,你也可以找到它。
如果我猜對了,你想要一個整潔的小 C# function 來找到最后一個重定向,對吧? 在這種情況下,應該這樣做:
string GetRedirectionFromDatabase(string requestUrl)
{
// Fetch redirect form DB, or if none exists return null
}
string GetFinalUrl(string requestUrl)
{
var redirection = GetRedirectionFromDatabase(requestUrl);
return redirection != null ? GetFinalUrl(redirection) : requestUrl;
}
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