如何修复此 LINQ 错误

发布于 2024-10-28 08:12:57 字数 886 浏览 1 评论 0原文

我期望的结果是：没有任何子项的记录列表，我的菜单表架构是：ID（长）、名称（字符串）、订单（int）、ParentID（长）

首先选择所有叶级子项身份证。获取除 ParentID 列中的值之外的所有 ID。然后通过在此处加入 leafID 来从菜单中进行选择

我的代码：

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 };

我收到错误：除了运算符是：

System.collections.generic.IEnumberable 不包含“Except”的定义和最佳方法重载 System.LINQ.queryable.Except(System. LINQ.IQueryalbe、System.collections.generic.IEnumberable) 有一些无效参数。

请帮我修复这个错误。多谢

原文

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

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

here my code :

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 };

i got a error : at Except operator is :

System.collections.generic.IEnumberable<long> does not contains a definition for 'Except' and the best method overload System.LINQ.queryable.Except<TSource>(System.LINQ.IQueryalbe<TSource>, System.collections.generic.IEnumberable<Tsource>) has some invalid arguments .

please help me fix this error. thanks a lot

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放低过去 2024-11-04 08:12:57

怎么样：

var items = from m in menus
            where !menus.Where(c => c.ParentID == m.ID).Any() 
            select new { 
                m.ID,
                m.Name};

在这里，您选择了每个没有 ParentID 引用的 menu 。

为了回应 @mmix 的评论，这里是生成的 SQL（使用 Linqpad）

SELECT [t0].[ID], [t0].[Name]
FROM [menus] AS [t0]
WHERE NOT (EXISTS(
    SELECT NULL AS [EMPTY]
    FROM [menus] AS [t1]
    WHERE [t1].[ParentID] = ([t0].[ID])
    ))

What about something like:

var items = from m in menus
            where !menus.Where(c => c.ParentID == m.ID).Any() 
            select new { 
                m.ID,
                m.Name};

Here you are selected every menu that doesn't have a ParentID referring back to it.

In response to comment by @mmix, here's the generated SQL (using Linqpad)

SELECT [t0].[ID], [t0].[Name]
FROM [menus] AS [t0]
WHERE NOT (EXISTS(
    SELECT NULL AS [EMPTY]
    FROM [menus] AS [t1]
    WHERE [t1].[ParentID] = ([t0].[ID])
    ))

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