I have this SQL query that gives the result I want. Please help me convert this to LINQ.
SELECT skill, sum (skillLevel)
FROM ReportView
WHERE jobTitle = 'Graphic Designer'
GROUP BY skill
The query gives the result as below.
skill (No column Name)
-------------------------------
Photoshop 10
Illustrator 8
I have tried this but I get anonymous type errors.
var results = db.ReportViews
.Where(x => x.jobTitle == "Graphic Designer")
.GroupBy(x => x.skill)
.Select(y =>
new
{
skill = y.Select(x => x.skill),
skillLevel = y.Sum(s => s.skillLevel)
}).ToList();
Related
trying to convert a query which has 2 levels of where in clauses to linq and getting some errors. Can anybody help me on this?
Original Query:
select id
from student
where suId
in (select suId
from subjects
where cid
in (select id
from chapters
where chapter='C203'))
LINQ query:
var query = (from s in dc.students
let subs = (from su in dc.subjects
where su.cid == Convert.ToInt32(from c in dc.Chapters
where c.chapter == 'Ç203'
select c.id) //Single chapter id will be returned
select su.suid)
where subs.Contains(s.sid)
select s.id).ToArray();
Am getting below 2 errors while compiling app
'System.Linq.IQueryable' does not contain a definition for 'Contains' and the best extension method overload 'System.Linq.ParallelEnumerable.Contains(System.Linq.ParallelQuery, TSource)' has some invalid arguments
Instance argument: cannot convert from 'System.Linq.IQueryable' to 'System.Linq.ParallelQuery'
Since Linq is lazy-loading everything you don't need to cram everything into a single statement; you can do something like this:
var chapterIds = dc.Chapters
.Where(c => c.Chapter == "C023")
.Select(c => c.Id);
var subjectIds = dc.Subjects
.Where(s => chapterIds.Contains(s.Cid))
.Select(s => s.Suid);
var students = dc.Students
.Where(s => subjectIds.Contains(s.Suid))
.Select(s => s.Sid)
.ToArray();
This way you can debug each subquery by looking at what it returns.
However, looking at your original select you can rewrite the whole thing as a Join and get rid of the bugging issue:
var students = dc.Chapters.Where(c => c.Chapter == "C023")
.Join(dc.Subjects,
c => c.Id,
s => s.Cid,
(chapter, subject) => subject)
.Join(dc.Students,
subj => subj.Suid,
student => student.Suid,
(subj, st) => st.Sid)
.ToArray();
I've got a class like the following:
public class Invoice
{
public int InvoiceId {get;set;}
public int VersionId {get;set;}
}
Each time an Invoice is modified, the VersionId gets incremented, but the InvoiceId remains the same. So given an IEnumerable<Invoice> which has the following results:
InvoiceId VersionId
1 1
1 2
1 3
2 1
2 2
How can I get just the results:
InvoiceId VersionId
1 3
2 2
I.e. I want just the Invoices from the results which have the latest VersionId. I can easily do this in T-SQL, but cannot for the life of me work out the correct LINQ syntax. I'm using Entity Framework 4 Code First.
Order by the VersionId, group them by InvoiceId, then take the first result of each group. Try this:
var query = list.OrderByDescending(i => i.VersionId)
.GroupBy(i => i.InvoiceId)
.Select(g => g.First());
EDIT: how about this approach using Max?
var query = list.GroupBy(i => i.InvoiceId)
.Select(g => g.Single(i => i.VersionId == g.Max(o => o.VersionId)));
Try using FirstOrDefault or SingleOrDefault in place of Single as well... it would give the same result although Single shows the intention better.
EDIT: I've tested both these queries with LINQ to Entities. They seem to work, so perhaps the issue is something else?
Option 1:
var latestInvoices = invoices.GroupBy(i => i.InvoiceId)
.Select(group => group.OrderByDescending(i => i.VersionId)
.FirstOrDefault());
EDIT: Changed 'Last' to 'FirstOrDefault', LINQ to Entities has issues with the 'Last' query operator.
Option 2:
var invoices = from invoice in dc.Invoices
group invoice by invoice.InvoiceId into invoiceGroup
let maxVersion = invoiceGroup.Max(i => i.VersionId)
from candidate in invoiceGroup
where candidate.VersionId == maxVersion
select candidate;
My version:
var h = from i in Invoices
group i.VersionId by i.InvoiceId into grouping
select new {InvoiceId = grouping.Key, VersionId = grouping.Max()};
Update
As was mentioned by Ahmad in the comments, the above query will return a projection. The version below will return a IQueryable<Invoice>. I use composition to build the query because I think it is more clear.
var maxVersions = from i in Invoices
group i.VersionId by i.InvoiceId into grouping
select new {InvoiceId = grouping.Key,
VersionId = grouping.Max()};
var latestInvoices = from i in Invoices
join m in maxVersions
on new {i.InvoiceId, i.VersionId} equals
new {m.InvoiceId, m.VersionId}
select i;
I am a newbie to Linq. I am trying to write a linq query to get a min value from a set of records. I need to use groupby, where , select and min function in the same query but i am having issues when using group by clause. here is the query I wrote
var data =newTrips.groupby (x => x.TripPath.TripPathLink.Link.Road.Name)
.Where(x => x.TripPath.PathNumber == pathnum)
.Select(x => x.TripPath.TripPathLink.Link.Speed).Min();
I am not able to use group by and where together it keeps giving error .
My query should
Select all the values.
filter it through the where clause (pathnum).
Groupby the road Name
finally get the min value.
can some one tell me what i am doing wrong and how to achieve the desired result.
Thanks,
Pawan
It's a little tricky not knowing the relationships between the data, but I think (without trying it) that this should give you want you want -- the minimum speed per road by name. Note that it will result in a collection of anonymous objects with Name and Speed properties.
var data = newTrips.Where(x => x.TripPath.PathNumber == pathnum)
.Select(x => x.TripPath.TripPathLink.Link)
.GroupBy(x => x.Road.Name)
.Select(g => new { Name = g.Key, Speed = g.Min(l => l.Speed) } );
Since I think you want the Trip which has the minimum speed, rather than the speed, and I'm assuming a different data structure, I'll add to tvanfosson's answer:
var pathnum = 1;
var trips = from trip in newTrips
where trip.TripPath.PathNumber == pathnum
group trip by trip.TripPath.TripPathLink.Link.Road.Name into g
let minSpeed = g.Min(t => t.TripPath.TripPathLink.Link.Speed)
select new {
Name = g.Key,
Trip = g.Single(t => t.TripPath.TripPathLink.Link.Speed == minSpeed) };
foreach (var t in trips)
{
Console.WriteLine("Name = {0}, TripId = {1}", t.Name, t.Trip.TripId);
}
I have a linq expression that returns transactions in groups. Each transaction has a numerical value and I now need to know what is the highest value from all the transactions returned. This value is held in a field called TransactionId
Here is the expression I am using to get the grouped list.
var transactions = ctx.MyTransactions
.Where (x => x.AdapterId == Id)
.GroupBy(x => x.DeviceTypeId);
I now need to write an expression that works on the “transactions” grouped list to find the “max” of the TransactionId field. I’ve tried different ideas but none seem to work with the grouped results. I’m new to linq so I’m not sure how to do this.
Have you tried finding the maximum in each group and then finding the maximum of that over all groups?
int max = transactions.Max(g => g.Max(t => t.TransactionId));
Or you could just query the database again:
int max = ctx.MyTransactions
.Where(x => x.AdapterId == Id)
.Max(t => t.TransactionId);
This will give you the max in each group
var transactionIds = ctx.MyTransactions
.Where (x => x.AdapterId == Id)
.GroupBy(x => x.DeviceTypeId,
g => new {
DeviceTypeId = g.Key,
MaxTransaction = g.Max(x => x.TransactionId)
});
I ended up with this horrible code below, I can't get a better result now.
What is a better way of doing that?
It's about this part of my database:
EDIT
A Patient has a Subscription to multiple MonitoringObjects. Target records refer to these Subscriptions. I want to retrieve the target records with the newest date per Subscription for a given Patient and a Category of MonitoringObjects. These target records may have different max dates, as Targets can be added for Subscriptions to MonitoringsObjects independently.
var subs = db.Subscriptions.Where(p => p.PatientID == patID).Where(p => p.MonitoringObject.Category.Name == "Medication");
var targets1 = from t in db.Targets
where subs.Contains(t.Subscription)
select t;
var maxTa = from t in db.Targets
group t by t.SubscriptionID
into g
select new
{
Ky = g.Key,
Date = g.Max(p => p.Date)
};
var targets2 = from t in targets1
where maxTa.Select(p => p.Ky).Contains( t.SubscriptionID ) &&
maxTa.Select(p => p.Date).Contains( t.Date )
select t;
I am not exactly sure what this is trying to achieve, or what your datamodel looks like, but something like this?
var subs = db.Subscriptions.Where(p => p.PatientID == patID).Where(p => p.MonitoringObject.Category.Name == "Medication");
var targets = subs
.SelectMany(s => s.Targets)
.Where(t => t.Date == t.Subscription.Targets.Max(_t => _t.Date))