Question

I have one List of objects that looks somthing like this

class Item
{
    int ItemId;
    string Name;
    DateTime CreatedDate;
    ... more properties, but not relevant ...
}

and another that holds votes

class Vote
{
    int ItemId;
    ... more properties, but not relevant ...
}

So the vote points to an item. I’ve gathered all the votes from the database, and stored them in a List

var votes = GetAllVotes().ToLookup(v => v.ItemId).OrderByDescending(v => v.Count());

Now I have a list that gives me the itemId’s with the most votes in a good list. Is there a way for me to sort my list of items based on the votes list?

var items = GetAllItems().OrderBy(i => i.CreatedDate);
//then I want to do something like this:
items.OrderBy(votes.Select(v => v.Key, v.Count())

So the goal here is that the items gets sorted by number of votes, and all the items with 0 votes keep their sorting by date.

Answer 1

It sounds like you want something like:

from item in GetAllItems()
join vote in GetAllVotes() on item.ItemId equals vote.VoteId into votes
orderby votes.Count() descending, item.CreatedDate
select new { Item = item, Votes = votes.Count() };

(I can put that in non-query-expression notation if you want, but it won’t be as neat.)