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Search Filter using lamba or linq - group by & take top record for each group.

Hello,

I am having some difficulties with getting the correct statement in lambda or linq.  


SQL Query
select count(me.schools_id) as numOfStudent, schools_name, members_exams_examdate
from members_exams as me
join schools as s on s.schools_id = me.schools_id
where members_exams_examdate = '8/19/16'
group by s.schools_id, members_exams_examdate, schools_name



This returns
+----------------------+---------------------------+-----------------------------------------+
|numOfStudent |  School Name       |  members exams examdate |
| 1                         | School A                |  8/19/2016                                |
| 4                         | School B                |  8/19/2016                                |
| 7                         | School C                |  8/19/2016                                |
| 21                       | School D                |  8/19/2016                               |
+-----------------------+---------------------------+----------------------------------------+


Controller:   Try1
	public ActionResult Index(string searchBy, string search)

			{
				DateTime convertedSearch;
				DateTime.TryParse(search, out convertedSearch);

					if (searchBy == "members_exams_examdate")
					{

						return View(from x in db.members_exams
									where x.members_exams_examdate == (convertedSearch)
									group x by x.schools_id
										into groups
										select groups.OrderBy(p => p.school.schools_name).First());

					
					}

					return View();
			}

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Return Error: The method 'First' can only be used as a final query operation. Consider using the method 'FirstOrDefault' in this instance instead.

Try2:   using  FirstorDefault
select groups.OrderBy(p => p.school.schools_name).FirstorDefault());

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Return Error: Error      1      'System.Linq.IOrderedEnumerable<Data.members_exams>' does not contain a definition for 'FirstorDefault' and no extension method 'FirstorDefault' accepting a first argument of type 'System.Linq.IOrderedEnumerable<Data.members_exams>' could be found (are you missing a using directive or an assembly reference?)      


Try3:
	return View(from x in db.members_exams
									where x.members_exams_examdate == (convertedSearch)
									group x by x.schools_id into y
									select new
									{
										schools_id = y.Key
									});

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Error: The model item passed into the dictionary is of type 'System.Data.Entity.Infrastructure.DbQuery`1[<>f__AnonymousTypef`1[System.Nullable`1[System.Int16]]]', but this dictionary requires a model item of type 'System.Collections.Generic.IEnumerable`1[Data.members_exams]'.

In the view I would like to group the records and display only the top record for each school.  Just like to table above.


I have tried a number of different things but no success.  

Thanks for the help.
0
lovettjay
Asked:
lovettjay
  • 2
1 Solution
 
Pawan KumarDatabase ExpertCommented:
Can you given me the final output you need , I will write that with SQL Query itself.
0
 
PortletPaulCommented:
Try using row_number and order that by the count descending
When that column rn is 1 it will be the top row you want
SELECT
      schools_name
    , members_exams_examdate
    , COUNT(me.schools_id)    AS numOfStudent
    , ROW_NUMBER() OVER (ORDER BY COUNT(*) DESC) AS rn
FROM members_exams AS me
JOIN schools AS s ON s.schools_id = me.schools_id
WHERE members_exams_examdate = '20160819'
GROUP BY
      schools_name
    , members_exams_examdate

Open in new window

By the way a date literal of yyyymmdd is THE safest to use in sql server.
Really don't recommend 2 digit years either

{+edit} please note I have changed this (edits via a phone just didn't work)
0
 
PortletPaulCommented:
by the way...

row_number() over(order by count(*) DESC) as rn

will always result in a single rn = 1 (i.e. one row)
& you might can  include other "tie breaker" column(s) in the ordering

if there is an equal count of students over more than one school, then instead you coud use

rank() over(order by count(*) DESC) as rn

and the rn=1 would apply to more then one school (i.e. rank number of 1)

your call
0

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