带有子查询，分组依据和具有的LINQ

Question

Ok,

I haven't spent much time with LINQ and I'm trying to write a query in C# to replace a select statement with a sub-query, group by and having. Here is the original query:

SELECT * FROM "Users" u1
WHERE u1.Name IN (
    SELECT u2.Name
    From "Users" u2
    WHERE Deleted IS NULL
    Group By u2.Name
    Having Count(UserName) > 1)     
ORDER BY "Name"

I can get the sub-query written like this:

            var query = 
                from u2 in db.Users
                group u2 by u2.Name into u2g
                where u2g.Count() > 1
                select u2g.Key;

But I'm struggling to make that the sub-query and get the complete list of users with duplicate names.

Any help would be appreciated.

Thanks

dbl

Answer 1

The group itself contains the users with duplicate names - you're selecting the wrong thing.

var dupeUsers = from user in users
                group user by user.Name into dupeNames
                where dupeNames.Count() > 1
                from userDupe in dupeNames
                orderby userDupe.Name
                select userDupe;

or, in method syntax

var dupeUsers = users.GroupBy(user => user.Name)
                     .Where(dupeNames => dupeNames.Count() > 1)
                     .SelectMany(user => user)
                     .OrderBy(user => user.Name);