如何使用TOP，COUNT和GROUP BY转换SQL语句以使用LINQ返回对象列表

Question

does anyone know how to convert this SQL statement to a LINQ to a List?

SELECT TOP(5) COUNT(Tickets.CategoryId), Categories.CategoryName
FROM Tickets 
INNER JOIN Categories ON Tickets.CategoryId = Categories.CategoryId
GROUP BY Categories.CategoryName
ORDER BY 1 DESC

The result would be something like this?

public static List<Categories> List()
{
    MyEntities db = new MyEntities();

    var categories = (from ticket in db.Ticket.Include("Category")
                        group ticket by ticket.Category.CategoryId into g
                        orderby g.Count() descending
                        select g.FirstOrDefault().Category).Take(5).ToList();

    return categories;

}

Answer 1

Have you tried creating a view from your query and calling that from Linq? It would look to Linq like a table. You could use the exact query you provided above.

You may be looking for a Linq only answer, but using a view would be a quick way to get there and you may get a slight boost in performance if you are hitting it very frequently.

I like to use DB for the things it is good at, and it looks to me like this might just be a good fit.

If you go with a Linq only solution, you might want to spend a few minutes trying the view and doing timing tests to see if it makes a difference in your app.

Answer 2

Looks like you just need to change the "SELECT" portion of your statement:

select new { Count = g.Count(), 
    CategoryName = g.FirstOrDefault().Category.CategoryName }