c# - 获取所有祖 parent ID 等于 1 的 child

Question

我在数据库中有如下三个表:

1.Design_Master_ParentMenus
    1.ParentMenuID      1--------
    2.Title                     |
2.Design_Master_Categories      |
    1.CategoryID         1------|---------
    2.Title                     |        |
    3.ParentMenuID        *------        |
3.Design_Master_TileItem                 |
    1.TileItemID                         | 
    2.Title                              |
    3.CategoryID          *---------------

现在我想从祖 parent 的 ParentMenuID 等于 1 的 Master_Design_TileItem 中获取所有项目。

到目前为止，我已经尝试了以下查询，但没有成功。

var g = from f in db.Design_Master_Categories
        where f.CategoryID == 1
        select f.CategoryID;

var v = from h in db.Design_Master_ParentMenus
        where h.ParentMenuID == g.FirstOrDefault()
        select h.ParentMenuID;

var result = from t in db.Design_Master_TileItem
             join c in db.Design_Master_Categories
             on t.CategoryID equals c.CategoryID
             join p in db.Design_Master_ParentMenus
             on c.ParentMenuID equals p.ParentMenuID
             where p.ParentMenuID == v.FirstOrDefault()
             select t;

但是当我运行程序时，我总是得到 result = null。

Answer 1

如何

    where f.CategoryID == 1

条件如下

Now I want to get all the Items from Master_Design_TileItem whose grandparent's ParentMenuID is equal to 1.

?你说，你想要 ParentMenuID = 1，而不是 CategoryID = 1。

你也没有说你的模型是如何设置的，但是有了适当的导航属性，你应该能够做到:

var result = from c in db.Design_Master_Categories
             from i in c.TileItems
             where c.ParentMenuID == 1
             select i;