我如何在表中写查询记录具有条件为parentID == 0和ID！=(parentID)的parentID

问题描述

在这里，我的LINQ查询要在Table Menu中获取记录，条件是parentID == 0(获取根菜单)和ID！=(parentID列表)(这是父ID列表是具有子菜单菜单的ID) ，我只想加载所有记录，包括没有子记录和子记录的根菜单:

Here i my LINQ query to get record in Table Menu with condition are parentID == 0(get root menu) and ID != (parentID list) (which is parent ID list is are id of menu record that have child), i just want to load all record includes root menu that have no children record and children record :

List<Menu> menus = MenuDAO.Instance.GetAll(); // Get All Record in Menu Table
var parentID = (from p in menus where p.ParentID != 0 select new {p.ParentID}).Distinct(); // Get unique ParentID in Menu Table
        List<int> numParentID = new List<int>();
        foreach (var a in parentID)
        {
            numParentID.Add(a.ParentID);
        } // assign to a list <int>
        this.ddlMenu.DataSource = from m1 in menus
                                  where !(numParentID).Contains((int)m1.ID) && m1.ParentID == 0
                                  select new { m1.ID, m1.Name };
        this.ddlMenu.Databind();

并且我运行此代码，我显示没有子项的记录，不显示儿童记录.有人帮我修复它.我的LINQ新手，非常感谢.

And i run this code , i display record that have no children, do not display chilren record. Somebody help me fix it. My new in LINQ , thanks a lot.

我在这里期望的结果是:没有任何子项的记录列表，我的菜单表架构是:ID，名称，顺序，ParentID.

The Result as i expect here is : list of record that do not have any children, my Menu table schema is : ID, Name, Order, ParentID.

推荐答案

建议

1-您无需在第一个选择中选择匿名对象，可以写为

1-You don't need to select an anonymous object in the first select, you could write as

var parentIDs = (from p in menus 
                 where p.ParentID != 0 
                 select p.ParentID).Distinct();

始终将集合命名为复数(parentIDs)

always a good practice to name collections as plural (parentIDs)

2-无需重复创建new List<>，因此您可以将所有内容写在一个查询中

2-No need to iterate to create a new List<>, so you can write all of them in one query

  List<int> numParentIDs = (from p in menus 
                            where p.ParentID != 0 
                            select p.ParentID).Distinct().ToList();

答案:首先选择所有叶级子代ID.获取除ParentID列中的值以外的所有ID.然后通过加入leafID从菜单中进行选择

Answer : first select all the leaf level children IDs. Get all ID except the values in the ParentID column. And then do a select from menu by joining the leafIDs

var leafMenuIDs = menus
                    .Select(m => m.ID)
                    .Except(menus.Select(m => m.ParentID).Distinct())                                         
                    .Distinct();


 this.ddlMenu.DataSource = from m in menus
                           join id in leafMenuIDs on m.ID equals id
                           select new { m.ID, m.Name };

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