How to use GroupBy using Dynamic LINQ

Question

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?

Nuncia

Don't you just mean mydata.Where(x => x.Shop == "HMV");? – Philbo

No, I am trying to GroupBy - not a Where clause. And bear in mind I am trying to achieve this with dynamic sql NOT standard lambda! – Nuncia

Answer 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);
   }
}

Itself

That is brilliant and seems to work but how would I iterate over the resulting groups? – Nuncia

just use ToList(); and If you have a new type than you have to select them new {shop... etc.} – Blouson

Not sure I understand - the groups are of type IGrouping - there is nowhere an option to do a ToList... – Nuncia

That works well thanks, but seems pretty inefficient since I have to create new List<T>'s out of the result in order to pass them on. Is there another way (like ToList<>)? – Nuncia

got pointed by someone to #12397313 – Nuncia

Answer 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

Debauched

Answer 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.

Blouson