如何访问在动态列表中的项目？ [英] How to access items in a dynamic list?

问题描述

我试图找出如何从一个动态的LINQ 。选择（字符串选择器）枚举结果.NET 4.5。动态LINQ来自 System.Linq.Dynamic 命名空间。

I am trying to figure out how to enumerate the results from a dynamic LINQ .Select(string selectors) in .NET 4.5. The dynamic linq comes from the System.Linq.Dynamic namespace.

编辑：我还包括 System.Linq的

我有一个看起来像这样的方法：

I have a method that looks like this:

    public void SetAaData(List<T> data, List<string> fields)
    {
        if (data == null || data.Count == 0)
        {
            return;
        }
        var dynamicObject = data.AsQueryable().Select("new (" + string.Join(", ", fields) + ")");
        _aaData = dynamicObject;
    }

如果我在code步骤，我可以检查 dynamicObject 和枚举它来查看结果（这是正确的）。问题是，我现在试图让我的单元测试通过了这一点，我已经无法访问任何东西dynamicObject。该 _aaData 字段定义为类型动态。

If I step through the code, I can examine dynamicObject and enumerate it to view the results (which are correct). The problem is that I am now trying to get my unit test to pass for this, and I've been unable to access anything in dynamicObject. The _aaData field is defined as the type dynamic.

在我的测试方法，我想这样的：

In my test method, I tried this:

        var hasDynamicProperties = new MyClass<MyType>();
        dgr.SetAaData(data, fields); // data is a List<MyType>
        Assert.IsTrue(hasDynamicProperties.AaData.Count > 0);

当我运行这个测试，我得到以下错误：

When I run this test, I get the following error:

MyTestingClass threw exception: 
Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: 'System.Linq.EnumerableQuery<DynamicClass1>' does not contain a definition for 'Count'

所以，我试图将其转换为一个列表：

So, I tried to cast it to a list:

Assert.IsTrue(dgr.AaData.ToList().Count() > 0);

这就造成了以下错误：

Which resulted in the following error:

Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: 'System.Linq.EnumerableQuery<DynamicClass1>' does not contain a definition for 'ToList'

所以，后来我抬头一看 System.Linq.EnumerableQuery＆LT; T＆GT; 此处的 http://msdn.microsoft.com/en-us/library/cc190116.aspx 。我看到所有的 .Count之间（）应该是一个有效的扩展方法，但是当我尝试它不工作。事实上，没有从该页面的工作方法时，我尝试一下。

So, then I looked up System.Linq.EnumerableQuery<T> here: http://msdn.microsoft.com/en-us/library/cc190116.aspx. I see all that .Count() is supposed to be a valid extension method, but it does not work when I try it. In fact, none of the methods from that page work when I try them.

我是什么做错了吗？

推荐答案

扩展方法不能适用于动态的对象，好像他们是成员的方法。

Extension methods can not be applied to dynamic objects as if they were member methods.

计数（）是 System.Linq.Queryable 定义的扩展方法，你可以直接调用它您的动态对象：

Count() is an extension method defined in System.Linq.Queryable, you can call it directly on your dynamic object:

Assert.IsTrue(Queryable.Count(hasDynamicProperties.AaData) > 0)

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