Question

我正在开发一个项目，我使用C＃来填充来自多个来源的单个MSSQL表格。

该表包含链接重定向信息（下面的示例结构）。

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

我是C＃的新手，需要编写某种递归查询来遍历每个redirectedurl，如果它在requesturl中，那么找到关联的redirectedurl。某些网址可能包含多个重定向。

Answer 1

由于您在SQL Server数据库中拥有此数据，因此一种可能的方法是带递归的CTE 。 This explanation一开始看起来有些混乱，但我想如果你向下滚动到示例，将会清楚如何做到这一点。

这里不重复整个解释，这是一个这样的查询的例子：

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

Answer 2

您可以创建一个字典，其中RequestedUrl为关键字，RedirectedUrl为值。所以一旦你找到requestedUrl你就可以找到它的redirectedURL，如果redirectedURL有一个redirectedURL，你也可以找到它。

Answer 3

如果我找对你，你想要一个整洁的小C＃函数来找到最后一个重定向，对吧？在这种情况下，应该这样做：

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;
}

C＃递归查询

3 个答案: