寫這個linq查詢有什麼更好的方法？

Question

SQL：

SELECT node.CategoryId, 
    node.CategoryName, 
    node.Description, 
    node.Lft, node.Rgt, 
    node.ShowOnMenu, 
(COUNT(parent.CategoryName) - 1) AS Level, 
(CASE WHEN node.Lft = node.Rgt - 1 THEN 'TRUE' ELSE 'FALSE' END) AS Leaf 
FROM Article_Category AS node, 
Article_Category AS parent 
WHERE node.Lft BETWEEN parent.Lft AND parent.Rgt 
GROUP BY node.CategoryId,node.CategoryName,node.Description,node.Lft,node.Rgt,node.ShowOnMenu 
ORDER BY node.Lft 

我的LINQ表達：

 var list = (from node in DbContext.Categories 
        from parent in DbContext.Categories 
        where node.Lft >= parent.Lft && node.Lft <= parent.Rgt 
        select new 
        { 
         node.CategoryId, 
         node.CategoryName, 
         node.Description, 
         node.Lft, 
         node.Rgt, 
         node.ShowOnMenu, 
         ParentName = parent.CategoryName, 
        } into x 
        group x by new 
        { 
         x.CategoryId, 
         x.CategoryName, 
         x.Description, 
         x.Lft, 
         x.Rgt, 
         x.ShowOnMenu, 
        } into g 
        orderby g.Key.Lft 
        select new 
        { 
         CategoryId = g.Key.CategoryId, 
         CategoryName = g.Key.CategoryName, 
         Description = g.Key.Description, 
         Lft = g.Key.Lft, 
         Rgt = g.Key.Rgt, 
         ShowOnMenu = g.Key.ShowOnMenu, 
         Level = g.Count() - 1, 
         IsLeaf = g.Key.Lft == g.Key.Rgt - 1 
        }).ToList(); 

我的問題：

1. LINQ的表達太長，有兩個「選擇新的'表達，我想知道如何縮短它？

2. linq查詢的相應擴展方法是什麼？如何使用擴展方法表達「從......哪裏......」？

Answer 1

第一select new .. into x我不明白爲什麼你需要，請嘗試刪除它，並寫group node by new...

"from...from"寫成一個lambda表達式是這樣的：

Categories.SelectMany(n => Categories, (n, p) => new { Node = n, Parent = p });