How to use GroupBy using Dynamic LINQ

问题

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

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();
}

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...

How would I go about this?

回答1:

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

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

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);
   }
}

回答2:

You may construct the group by expression dynamically or give a try to this Dynamic LINQ library presented on ScottGu's page:
http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx

回答3:

This is the method I have copied from DynamicQuery:

public static IQueryable GroupBy(this IQueryable source, string keySelector, string elementSelector, params object[] values) {..}

In my example I provide the keySelector and the elementSelector.

listAlbums.AsQueryable().GroupBy("it.Shop", "it").Select("Author"); You can use new with GroupBy or with select for the new types.

It like this in OOP class.

来源：https://stackoverflow.com/questions/20329558/how-to-use-groupby-using-dynamic-linq

标签

linq

dynamic-linq