LINQ join tables and count groups - linq

Question

I'm trying to write a linq query that performs this SQL for my Entity Framework connection:
SELECT
l.Site_Name, COUNT(*)
FROM
vw_Subnet s
INNER JOIN
vw_Lab_Space l ON l.Lab_Space_id = s.Lab_Space_Id
WHERE
s.Lab_Space_Id IS NOT NULL
AND s.MM_Space_Id IS NOT NULL
GROUP BY
l.Site_Name
ORDER BY
2 DESC
but I can't figure out the right syntax. Without the WHERE clause I had tried this, but it's not actually doing the GROUP BY part like all the examples I've seen imply it should be:
from l in db.vw_Lab_Space.AsNoTracking()
join s in db.vw_Subnet.AsNoTracking()
on l.Lab_Space_Id equals s.Lab_Space_Id into joined
select new SiteCount {
Site = l.Site_Name,
Count = joined.Count()
};
I'm getting back a SiteCount with repetitive Site values.

Answer 1

You forgot to write the specification about what you want to achieve, but it seems to be the following.
You have a sequence of vwLabSpaces, where every vwLabSpace has a LabSpaceId and a SiteName.
You also have a sequence of vwSubnets where every vwSubnet has a LabSpaceId
You want to join these two sequences on common LabSpaceId. Then you want to group the joined elements into groups of element sthat have the same value for SiteName (so every element in one group has the same SiteName)
The end result should be a list of the common siteNames of each group and the number of elements in each groups.
In baby steps:
// your two sequences:
IQueryable<VwLabSpace> vwLabSpaces = myDbContext.VwLabSpaces;
IQueryable<VwSubNet> vwSubNets = myDbContext.VwSubNext;
// join on common LabSpaceId
var joinedItems = vwLabSpaces.Join(vwSubNets, // join the two sequences
vwLabSpace => vwLabSpace.LabSpaceId, // from every vwLabSpace take the LabSpaceId
vwSubNet => vwSubNet.LabSpaceId, // from every vwSubNet take the LabSpaceId
(vwLabSpace, vwSubNet => new // when they match make a new
{ // joined object containing
VwLabSpace = vwLabSpace, // both matching objects
VwSubNet = vwSubNet,
});
// make groups of joinedItems that have same SiteName
var groupsWithSameSiteName = joinedItems
.GroupBy(joinedItem => joinedItem.VwLabSpace.SiteName);
// finally: get the common SiteName (= Key) and count the elements of each group
var result = groupsWithSameSiteName
.Select(group => new // from every group make one new object
{ // with two properties:
SiteName = group.Key, // the common SiteName of all elements in the group
Count = group.Count(), // and the number of elements in the group
});
TODO: if desired make one big LINQ statement. Because of lazy execution this won't make a difference.
As you only use the SiteName of each joined item, you don't have to combine the complete joining objects:
// join on common LabSpaceId
var joinedItems = vwLabSpaces.Join(vwSubNets, // join the two sequences
vwLabSpace => vwLabSpace.LabSpaceId, // from every vwLabSpace take the LabSpaceId
vwSubNet => vwSubNet.LabSpaceId, // from every vwSubNet take the LabSpaceId
(vwLabSpace, vwSubNet) => // when they match
vwLabSpace.SiteName); // keep the SiteName