如何GROUPBY使用动态LINQ使用 [英] How to use GroupBy using Dynamic LINQ

问题描述

我试图做一个GROUPBY使用动态LINQ，但有麻烦它的工作。

I am trying to do a GroupBy using Dynamic LINQ but have trouble getting it to work.

这是说明问题的一些示例代码：

This is some sample code illustrating the problem:

List<dtoMyAlbum> listAlbums = new List<dtoMyAlbum>();
for (int i = 0; i < 5000; i++)
{
    dtoMyAlbum album = new dtoMyAlbum
    {
        Author = "My Author",
        BookID = i,
        CurrSymbol = "USD",
        Price = 23.23,
        Shop = i % 3 == 0 ? "TESCO" : "HMV"
    };
    listAlbums.Add(album);
}

IQueryable<dtoMyAlbum> mydata = listAlbums.AsQueryable();
int count = mydata.Count();

//var mydataGrouped = mydata.GroupBy(a => a.Shop);      // <-- this works well (but is not dynamic....)
var mydataGrouped = mydata.GroupBy("Shop");             // <-- does not compile but is kind of what I want...

foreach (var group in mydataGrouped)
{
    //count = group.Count();
}

我意识到我缺少了elementSelector在GROUPBY超载，但所有我想做的是（在这种情况下）两套dtoMyAlbum的对象，所以我想选择所有集合的所有元素...

I realise that I am missing the 'elementSelector' in the GroupBy overload but all I want to do is to end up with (in this case) two sets of dtoMyAlbum objects so I wish to select ALL elements for all sets...

我怎么会落得去呢？

推荐答案

有是默认的是定义，你可以用它来返回匹配的元素：

There is default it defined, you can use it to return matched elements:

var mydataGrouped = mydata.GroupBy("Shop", "it");  

要通过结果迭代还应额外选择元素命名，并使用动态取值：

To iterate through results you should additionally Select elements to name it and use dynamics:

var mydataGrouped = mydata.GroupBy("Shop", "it").Select("new (it.Key as Shop, it as Albums)");

foreach (dynamic group in mydataGrouped)
{
   foreach (dynamic album in group.Albums)
   {
      Console.WriteLine(album.Author);
   }
}

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