Linq中的.Include().Where().Select()到实体查询 [英] .Include() .Where() .Select() in Linq to Entities Query

问题描述

我有一个Linq查询，查询以下表:具有一对多链接的任务:TaskLinks和TaskLinks有一对一链接到名为Entities的表.

I have a Linq query that queries the following tables: Tasks with a one-to-many link to: TaskLinks and TaskLinks has a one-to-one link to a Table called Entities.

我正在尝试选择任务，希望(通过.include)加载任务链接，然后选择链接到任务链接的实体.但是我需要过滤任务(按访问级别int)和任务链接，以便不包括任何非活动(布尔)记录.

I am trying to select the task, eager load (via .Include) the TaskLinks and select the Entity linked to the TaskLink. But I need to filter the Task (by Access Level int) and the TaskLinks so that I don't include any Inactive (bool) records.

这是我的Linq查询:

Here is my Linq query:

Tasks.Where(t => t.AccessLevel <= 5)
     .Include(tl => tl.TaskLinks.Where(tl2=> tl2.IfInactive == false)
     .Select(tls => tls.Entity))

我在LinqPad中运行此查询，但出现以下我不理解的错误:

I run this query in LinqPad, and I get the following error which I do not understand:

ArgumentException:包含路径表达式必须引用在类型上定义的导航属性.使用虚线路径作为参考导航属性，并使用选择"运算符作为集合导航属性. 参数名称:路径

ArgumentException: The Include path expression must refer to a navigation property defined on the type. Use dotted paths for reference navigation properties and the Select operator for collection navigation properties. Parameter name: path

如何重新编写此查询，以便筛选出包含的任务链接，然后选择实体?

How can I re-write this query so I can filter the Included TaskLinks, and select the Entity?

先谢谢您！

鲍勃

推荐答案

.Include(...)向查询提供程序建议"以急于加载导航属性.在这种情况下，它不会这样做b/c您的结果不是Task实体，而是Entity实体.

.Include(...) 'suggests' to the query provider to eager load the navigation property. In this case, it won't do so b/c your results are not Task entities, they're Entity entities.

无论如何，您都不会在include语句中过滤集合导航属性(这是导致您出错的原因).

In any case, you don't filter a collection navigation property in an include statement (which is what's causing your error).

您需要以下内容:

// start with Tasks, filter by AccessLevel
Tasks.Where( t => t.AccessLevel <= 5 )
    // get the TaskLinks for each Task
    .SelectMany( t => t.TaskLinks )
    // filter TaskLinks by IfInactive == false
    .Where( tl => !tl.IfInactive )
    // update to keep the hierarchy you want
    .GroupBy( tl => tl.Task )
    .Select( g => new
        {
            Task = g.Key,
            FilteredTaskLists = g.Select( tl => new 
                {
                    TaskList = tl,
                    Entity = tl.Entity
                } )
        } );

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