Counting grouped data with Linq to Sql

I have a database of documents in an array, each with an owner and a document type, and I'm trying to get a list of the 5 most common document types for a specific user.

var docTypes = _documentRepository.GetAll()
                   .Where(x => x.Owner.Id == LoggedInUser.Id)
                   .GroupBy(x => x.DocumentType.Id);

This returns all the documents belonging to a specific owner and grouped as I need them, I now need a way to extract the开发者_StackOverflow社区 ids of the most common document types. I'm not too familiar with Linq to Sql, so any help would be great.

This would order the groups by count descending and then take the top 5 of them, you could adapt to another number or completely take out the Take() if its not needed in your case:

var mostCommon = docTypes.OrderByDescending( x => x.Count()).Take(5);

To just select the top document keys:

var mostCommonDocTypes = docTypes.OrderByDescending( x => x.Count())
                                 .Select( x=> x.Key)
                                 .Take(5);

You can also of course combine this with your original query by appending/chaining it, just separated for clarity in this answer.

Using the Select you can get the value from the Key of the Grouping (the Id) and then a count of each item in the grouping.

var docTypes = _documentRepository.GetAll()                   
.Where(x => x.Owner.Id == LoggedInUser.Id)                   
.GroupBy(x => x.DocumentType.Id)
.Select(groupingById=> 
  new
  {
    Id = groupingById.Key,
    Count = groupingById.Count(),
  })
.OrderByDescending(x => x.Count);