c# – 编写这个linq查询的更好方法是什么？

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.ShowOnMenu
ORDER BY node.Lft

我的linq表达式：

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,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();

我的问题：

> linq表达式太长,有两个’select new’表达式,我想知道如何缩短它？
> linq查询的相应扩展方法是什么？如何用Extension方法表达“from … from … where …”？

解决方法

第一个选择新..进入x我不明白为什么你需要,尝试删除它并写新的组节点…

“from … from”写成lambda表达式,如下所示：

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