This is my query:
Dim vendorId = 1, categoryId = 1
Dim styles = From style In My.Context.Styles.Include("Vendor") _
Where style.Vendor.VendorId = vendorId _
AndAlso (From si In style.StyleItems _
Where si.Item.Group.Category.CategoryId = _
categoryId).Count > 0 _
Distinct
I have the feeling that I can improve the performance, cuz the above query is (correct me if I am wrong) performs 2 round-trips to the server; 1 time by the Count and then when it's executed.
I want to send this Count thing to the DB so it should be only one round trip to the server.
Even it's not the exact thing, this is actually what I need:
SELECT DISTINCT Style.*
FROM Style INNER JOIN
Vendor ON Style.VendorId = Vendor.VendorId INNER JOIN
StyleItem ON Style.StyleId = StyleItem.StyleId INNER JOIN
Item ON StyleItem.ItemId = Item.ItemId INNER JOIN
[Group] ON Item.GroupId = [Group].GroupId INNER JOIN
Category ON [Group].CategoryId = Category.CategoryId
WHERE (Style.VendorId = #vendorid) AND (Category.CategoryId = #CategoryId)
I wish I could use this SPROC (i.e. function import etc.), but I need to Include("Vendor"), which constraints me to do it with Linq.
Any kind of suggestion will be really welcommed!
It is probably not doing two trips to the database. It will get optimized before it is executed, and nothing gets executed until you try the read the data.
Normally I check the SQL that is created using SQL Profiler. I have also found LinqPad to be very usefull.
Related
What is the difference between the query in this post:
Save LINQ Query As Variable To Call Another LINQ Query
var parentLoc = (from a in db.PartsLocations
where a.LocationName == aContainer
select a.ParentLocation);
var locations = (from b in db.PartsLocations
where b.LocationID == parentLoc
select b).ToList();
to the following example from this post.
Dim persVogel = From p In db.People
Where p.LastName = "Vogel"
Select p
Dim persVogelPHVIS = From pp In persVogel
Where pp.Company.Name = "PHVIS"
Select pp
Both of these have declared 2 queries and use the first query variable into second query.
What is the reason to use Single() in the first example but was not used in visualstudiomagazine.com article? Thanks
The two samples are fundamentally different.
First Sample
I think you pasted this one incorrectly...from the referenced question, the query should be:
var parentLoc = (from a in db.PartsLocations
where a.LocationName == aContainer
select a.ParentLocation).Single();
var locations = (from b in db.PartsLocations
where b.LocationID == parentLoc
select b).ToList();
(I am going to assume that LocationID and ParentLocation are typed as int.)
In this sample parentLoc is an int - a single instance of a ParentLocation value, obtained from the PartsLocations table. So what you get is an int.
The second linq statement sources its records also from the PartsLocations table. It uses parentLoc to identify records within that table (e.g. where b.LocationID == parentLoc). What you get at the end is a set of PartsLocations records.
The .Single() call is made because you want to compare the result to LocationID in the second statement, and cannot compare int to IEnumerable<int>.
Second Sample
Dim persVogel = From p In db.People
Where p.LastName = "Vogel"
Select p
Dim persVogelPHVIS = From pp In persVogel
Where pp.Company.Name = "PHVIS"
Select pp
In the second sample, persVogel is a subset of records from the People table (specifically, the subset of people with LastName == "Vogel") - so what you get is a set of People records.
The second linq statement is based on this subset of records (From pp In persVogel) and further filters them down to records where pp.Company.Name = "PHVIS". What you get is still a set of People records.
These two statements could easily be compressed into one single statement:
Dim persVogelPHVIS = From p In db.People
Where p.LastName = "Vogel"
AndAlso p.Company.Name = "PHVIS"
Select p
You will still get a set of People records at the end.
At my job our main application was written long ago before n-tier was really a thing, ergo - it has tons and tons of business logic begin handled in stored procs and such.
So we have finally decided to bite the bullet and make it not suck so bad. I have been tasked with converting a 900+ line sql script to a .NET exe, which I am doing in C#/Linq. Problem is...for the last 5-6 years at another job, I had been doing Linq exclusively, so my SQL has gotten somewhat rusty, and some of thing I am converting I have never tried to do before in Linq, so I'm hitting some roadblocks.
Anyway, enough whining.
I'm having trouble with the following sql statement, I think due to the fact that he is joining on a temp table and a derived table. Here's the SQL:
insert into #processedBatchesPurgeList
select d.pricebatchdetailid
from pricebatchheader h (nolock)
join pricebatchstatus pbs (nolock) on h.pricebatchstatusid = pbs.pricebatchstatusid
join pricebatchdetail d (nolock) on h.pricebatchheaderid = d.pricebatchheaderid
join
( -- Grab most recent REG.
select
item_key
,store_no
,pricebatchdetailid = max(pricebatchdetailid)
from pricebatchdetail _pbd (nolock)
join pricechgtype pct (nolock) on _pbd.pricechgtypeid = pct.pricechgtypeid
where
lower(rtrim(ltrim(pct.pricechgtypedesc))) = 'reg'
and expired = 0
group by item_key, store_no
) dreg
on d.item_key = dreg.item_key
and d.store_no = dreg.store_no
where
d.pricebatchdetailid < dreg.pricebatchdetailid -- Make sure PBD is not most recent REG.
and h.processeddate < #processedBatchesPurgeDateLimit
and lower(rtrim(ltrim(pbs.pricebatchstatusdesc))) = 'processed' -- Pushed/processed batches only.
So that's raising an overall question first: how to handle temp tables in Linq? This script uses about 10 of them. I currently have them as List. The problem is, if I try to .Join() on one in a query, I get the "Local sequence cannot be used in LINQ to SQL implementations of query operators except the Contains operator." error.
I was able to get the join to the derived table to work using 2 queries, just so a single one wouldn't get nightmarishly long:
var dreg = (from _pbd in db.PriceBatchDetails.Where(pbd => pbd.Expired == false && pbd.PriceChgType.PriceChgTypeDesc.ToLower().Trim() == "reg")
group _pbd by new { _pbd.Item_Key, _pbd.Store_No } into _pbds
select new
{
Item_Key = _pbds.Key.Item_Key,
Store_No = _pbds.Key.Store_No,
PriceBatchDetailID = _pbds.Max(pbdet => pbdet.PriceBatchDetailID)
});
var query = (from h in db.PriceBatchHeaders.Where(pbh => pbh.ProcessedDate < processedBatchesPurgeDateLimit)
join pbs in db.PriceBatchStatus on h.PriceBatchStatusID equals pbs.PriceBatchStatusID
join d in db.PriceBatchDetails on h.PriceBatchHeaderID equals d.PriceBatchHeaderID
join dr in dreg on new { d.Item_Key, d.Store_No } equals new { dr.Item_Key, dr.Store_No }
where d.PriceBatchDetailID < dr.PriceBatchDetailID
&& pbs.PriceBatchStatusDesc.ToLower().Trim() == "processed"
select d.PriceBatchDetailID);
So that query gives the expected results, which I am holding in a List, but then I need to join the results of that query to another one selected from the database, which is leading me back to the aforementioned "Local sequence cannot be used..." error.
That query is this:
insert into #pbhArchiveFullListSaved
select h.pricebatchheaderid
from pricebatchheader h (nolock)
join pricebatchdetail d (nolock)
on h.pricebatchheaderid = d.pricebatchheaderid
join #processedBatchesPurgeList dlist
on d.pricebatchdetailid = dlist.pricebatchdetailid -- PBH list is restricted to PBD purge list rows that have PBH references.
group by h.pricebatchheaderid
The join there on #processedBatchesPurgeList is the problem I am running into.
So uh...help? I have never written SQL like this, and certainly never tried to convert it to Linq.
As pointed out by the comments above, this is no longer being rewritten as Linq.
Was hoping to get a performance improvement along with achieving better SOX compliance, which was the whole reason for the rewrite in the first place.
I'm happy with just satisfying the SOX compliance issues.
Thanks, everyone.
First of all I have to admit I'm very much a novice in Linq and Lambda expressions.
I'm trying to get the following SQL statement into a Linq statement (using lamda expressions):
select *
from dbo.tblStockTransfers t1,
dbo.tblSuppliers t2
where t1.SupplierID = t2.SupplierID
and t2.WarehouseID in (1,2,3)
and t1.GoodsPickedUp = 1
and Not exists
(select 1 from dbo.tblStockTransfers t3
where t3.TransferOutID = t1.TransferID and t3.TransferConfirm = 1)
My class StockTransfer is an aggregate root and has it's own repository.
Now so far I got the following (the variable allowedWarehouses contains the list of warehouse IDs):
Return GetObjectSet().Where(Function(st) allowedWarehouses.Contains(st.Supplier.WarehouseID) And st.GoodsPickedUp = True)
This works fine, but obviously is missing the " and not exists ..." part (the last 3 lines of the SQL code at the top of this posting).
I know that Linq doesn't have a "not exists", but you can use the "Any" method for this.
Here's a working example of this elsewhere in my code:
Return GetObjectSet().Where(Function(sw) sw.Active = True And Not sw.Suppliers.Any(Function(sp) sp.WarehouseID = sw.Id))
This works fine and will give me any warehouses which are not linked to a supplier yet.
As you can see in the above example this is fine as I'm referring to the related table "Suppliers".
However, in the SQL code I'm now trying to convert into Linq, the "not exists" is not on a linked table but on itself. Is there a way I can create a 2nd reference on the main table and use that in a ".. not ..any" part. Maybe something like:
Return GetObjectSet().Where(Function(st) allowedWarehouses.Contains(st.Supplier.WarehouseID) And st.GoodsPickedUp = True And Not st2.Any(st2.TransferOutID = st.TransferId and st2.TransferConfirm = true)
But I don't know how to define st2 (i.e. in this case st2 would be a 2nd alias to StockTransfer).
Any Help would be greatly appreciated.
This is not the answer to the question, but it is a work-around which does get me the result I need:
Dim st1 As List(Of StockTransfer) = GetObjectSet.Where(Function(st) allowedWarehouses.Contains(st.Supplier.WarehouseID) And st.GoodsPickedUp = True).ToList
Dim st2 As List(Of StockTransfer) = GetObjectSet.Where(Function(st) st.TransferConfirm = True).ToList
For Each st As StockTransfer In st2
st1.RemoveAll(Function(x) x.Id = st.TransferOutID)
Next
Return st1
I'm obviously cheating by splitting out the query in 2 parts, where each part ends up in a list and then I remove from list 1 any items which I've got in list 2 (removing the ones which would normally be ignored by the "not exists" part).
However, I would love to hear it if anyone can come up with a working solution using Linq and lambda expressions (as this does feel a bit like a cheat).
I would do it something like this:
Dim lsWareHouseIds As New List(Of Integer)() From {1,2,3}
dim obj= ( _
From t1 in db.tblStockTransfers _
join t2 in db.tblSuppliers _
on t1.SupplierID equals company.SupplierID _
where lsWareHouseIds.Contains(t2.WarehouseID) _
andalso t1.GoodsPickedUp =1 _
andalso Not _
(
from t3 in db.tblStockTransfers _
where t3.TransferConfirm=1 _
select t3.TransferOutID _
).Contains(t1.TransferID) _
select t1 _
)
I did see you comment and you answer. Can't you do like this:
GetObjectSet.Where(Function(st) _
allowedWarehouses.Contains(st.Supplier.WarehouseID) And st.GoodsPickedUp = True _
Andalso Not _
GetObjectSet.Where(Function(st) _
st.TransferConfirm = True).Any(Function(x) x.Id = st.TransferOutID)).ToList
My app consolidates data from other DBs for reporting purposes. We can't link the databases, so all the data processing has to be done in code - this is fine as we want to allow manual validation during the imports.
Certain users will be able to start an update through the Silverlight 4 front end.
I have 3 tables in database x that are fed from one EF4 Model (ModelX). I want to join those tables together, select specific columns and return the result as a new entity that exists in a different EF4 Model (ModelY). I'm using this query:
var myQuery = from i in DBx.table1 from it in DBx.table2 from h in DBx.table3 where (i.id==it.id && h.otherid == i.otherid) select new ModelYServer {Name = i.name,Thing = it.thing, Stuff = h.stuff};
The bit i'm stuck on, is how to execute that query, and wait until the Asynchronous call has completed. Normally, i'd use:
DomainContext.Load<T>(myQuery).Completed += (sender,args) =>
{List<T> myList = ((LoadOperation<T>)sender.Entities.ToList();};
but I can't pass myQuery (an IEnumerable) into the DomainContext.Load() as that expects an EntityQuery. The dataset is very large, and is taking up to 30 seconds to return, so I definitely need to wait before continuing.
So can anyone tell me how I can wait for the IEnumerable query to complete, or suggest a better way of doing this (there very likely is one).
Thanks
Mick
One simple way is just to force it to evaluate by calling ToList:
var query = from i in DBx.table1
join it in DBx.table2 on i.id equals it.id
join h in DBx.table3 on i.otherid equals h.otherid
select new ModelYServer {
Name = i.name,
Thing = it.thing,
Stuff = h.stuff
};
// This will block until the results have been fetched
var results = query.ToList();
// Now use results...
(I've changed your where clause into joins on the earlier tables, as that's what you were effectively doing and this is more idiomatic, IMO.)
I have a problem trying to do a couple of things with linq joins... currently I have a
group in linq that gives two columns, basically a count of tickets by location. Well now I'm trying to add a join that will join on the ticketID columns of two different tables Tickets and Comments.
I'm having a hell of a time trying to convert the sql join into Linq, less alone merging that into my original total count linq statement...somebody please help!
Original Linq statement:
From p In NewTickets _
Where p.TDate > "06/01/2009 12:00:00AM" And p.TDate < "07/01/2009 12:00:00PM" _
Group p By p.LocationID _
Into Count() _
Select _
LocationID, _
NoOfTickets = Count _
Order By NoOfTickets Descending
Join I need merged into Linq statement:
SELECT *
FROM NewTickets as p
LEFT OUTER JOIN NewComments AS c ON p.TicketID = c.TicketID
WHERE (p.TDate > '06/01/2009 12:00:00AM') And (p.TDate < '07/01/2009 12:00:00PM')
AND c.Comment Like '%ali%'
THANK YOU!
If you add a relationship in the linq to sql designer between NewTickets and NewComments, properties will be created on those classes to navigate.
Queries that use those properties will automatically translate into the join. For example:
from t in db.NewTickets
where t.NewComments.Any(nc => nc.Comment.Contains("ali"))
group t by t.LocationID into g
select new {LocationID = g.Key, NoOfTickets = g.Count()} into x
order x by x.NoOfTickets descending
select x;
Apologies for the C# code examples.
Also, I'd like to point out that the left join in your sql is moot - tickets that have no comments will be removed by the ali criteria. An inner join will do fine.
Something like this
var movies = NewTickets.Join(NewComments, x => x.TicketID, y => y.TicketID, (x, y) => x).ToList();
That was it...for the most part...I'm going to have to attack this a different way as now I'm getting a count that apparently from comments as my total has ballooned from under 200 to almost 1300...each ticket will have on average around 5 or so comments so that's why I assuming this just shooting from the hip...
Thank you David and no problem with the C# (as much that I have translated, you think I'd be using it by now).
For anyone using VB that would like to see the same in VB, here you go:
Dim q = From e In db.NewTickets _
Where e.NewComments.Any(Function(nc) nc.Comment.Contains("ali")) _
Group e By e.LocationID _
Into Count() _
Select _
LocationID, _
NoOfTickets = Count _
Order By NoOfTickets Descending