Is a dynamic pivot using LINQ possible? - linq

Question

I have a T-SQL 2005 query which returns:
pid propertyid displayname value
----------- ----------- --------------- ---------------
14270790 74 Low Price 1.3614
14270790 75 High Price 0
14270791 74 Low Price 1.3525
14270791 75 High Price 0
14270792 74 Low Price 1.353
14270792 75 High Price 0
14270793 74 Low Price 1.3625
14270793 75 High Price 0
14270794 74 Low Price 1.3524
14270794 75 High Price 0
What I would like to do is essentially pivot on the displayname field, hopefully producing:
pid Low Price High Price
14270790 1.3614 0
14270791 1.3525 0
14270792 1.353 0
14270793 1.3625 0
14270794 1.3524 0
(Not sure how the propertyid field would be output, so I left it out (was hoping it would simply sit alongside the Low Price and High Price fields, to indicate their IDs, but I don't think that will work.)
The problem is that the content of the original displayname field is dynamic - it is produced from a join with a PropertyName' table, so the number of pivoted columns is variable. It could therefore containHigh Price,Low Price,OpenandClose`, depending on what the join with that table returns.
It is, of course, relatively easy (regardless of the trouble I'm having writing the initial query!) to produce this pivot in a fixed query or stored proc. However, is it possible to get LINQ to generate a SQL query which would name each column to be produced rather than having to write a dynamic (probably in a stored proc) query which lists out the column names?
Thanks,
Matt.

Answer 1

I'll give you a sample with a different data (that I needed). You can adapt that to your need. Note only two linq queries are used, most of the other fluff is to convert a list into a datatable.
var data = new[] {
new{Student=1, Subject="English", Marks=40},
new{Student=1, Subject="Maths", Marks=50},
new{Student=1, Subject="Science", Marks=60},
new{Student=1, Subject="Physics", Marks=70},
new{Student=1, Subject="Chemistry", Marks=80},
new{Student=1, Subject="Biology", Marks=90},
new{Student=2, Subject="English", Marks=4},
new{Student=2, Subject="Maths", Marks=5},
new{Student=2, Subject="Science", Marks=6},
new{Student=2, Subject="Physics", Marks=7},
new{Student=2, Subject="Chemistry", Marks=8},
new{Student=2, Subject="Biology", Marks=9}
};
/*Here the pivot column is the subject and the static column is student
group the data against the static column(s)*/
var groups = from d in data
group d by d.Student into grp
select new
{
StudentId = grp.Key,
Marks = grp.Select(d2 => new { d2.Subject, d2.Marks }).ToArray()
};
/*get all possible subjects into a separate group*/
var subjects = (from d in data
select d.Subject).Distinct();
DataTable dt = new DataTable();
/*for static cols*/
dt.Columns.Add("STUDENT_ID");
/*for dynamic cols*/
foreach (var subject in subjects)
{
dt.Columns.Add(subject.ToString());
}
/*pivot the data into a new datatable*/
foreach (var g in groups)
{
DataRow dr = dt.NewRow();
dr["STUDENT_ID"] = g.StudentId;
foreach (var mark in g.Marks)
{
dr[mark.Subject] = mark.Marks;
}
dt.Rows.Add(dr);
}

Answer 2

This is the closest I could get, but it's not LINQ...
create table #t
(
pointid [int],
doublevalue [float],
title [nvarchar](50)
)
insert into #t
select
distinct top 100
v.pointid, v.doublevalue, p.title
from [property] p
inner join pointvalue v on p.propertyid = v.propertyid
inner join point pt on v.pointid = pt.pointid
where v.pointid in (select top 5 p.pointid from point p where p.instanceid = 36132)
declare #fields nvarchar(250)
set #fields = (select STUFF((SELECT N',[' + title + ']' FROM [property] FOR XML PATH('')), 1, 1, N''))
--select #fields
declare #sql nvarchar(500)
set #sql = 'select * from #t
pivot
(
sum(doublevalue)
for [title] in ('+#fields+')
) as alias'
--select #sql
exec (#sql)
drop table #t
The kicker is that I'm simply asking for every entry in the Property table, meaning there's a lot of columns, in the resulting pivot, which have NULL values.

Answer 3

the code I think is like this:
var list = from table in Property
group table by table.pid into g
select new
{
pid = g.key,
LowPrice = g.Where(w => w.pid== g.key && w.priceType == "low").Select(s => s.value).FirstorDefault(),
HighPrice = g.Where(w => w.pid== g.key && w.priceType == "high").Select(s => s.value).FirstorDefault(),
};
Hope it can help you and have a nice day.