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Linq Left Outer Join with Count

I want to create this SQL query:
SELECT
a.[Seat],
b.[PlayerId],
b.[UserName],
b.[NickName],
COUNT(c.PlayerId) AS Trophy
FROM [dbo].[tbl_PlayerTableSeat] AS a
INNER JOIN [dbo].[tbl_Player] AS b ON a.[PlayerId] = b.[PlayerId]
INNER JOIN [dbo].[tbl_GameVirtualTable] AS d ON d.GameVirtualTableId = a.GameVirtualTableId
LEFT OUTER JOIN [dbo].[tbl_PlayerTableWinning] AS c ON a.[PlayerId] = c.[PlayerId] AND c.GameTableId = d.GameTableId
WHERE a.GameVirtualTableId = 36
GROUP BY a.[Seat], b.[PlayerId], b.[UserName], b.[NickName]
I have this Linq
var virtualTableSeatList = (from s in db.PlayerTableSeat
join p in db.Player on s.PlayerId equals p.PlayerId
join v in db.GameVirtualTable on s.GameVirtualTableId equals v.GameVirtualTableId
join w in db.PlayerTableWinning on new { X1 = s.PlayerId, X2 = v.GameTableId } equals new { X1 = w.PlayerId, X2 = w.GameTableId } into gj
from g in gj.DefaultIfEmpty()
where s.GameVirtualTableId == virtualGameTableId
group new { p, s } by new { p.PlayerId, s.Seat, p.NickName, p.UserName } into grp
select new VirtualTableSeatDto
{
PlayerId = grp.Key.PlayerId,
Seat = grp.Key.Seat,
NickName = grp.Key.NickName,
UserName = grp.Key.UserName,
Trophy = grp.Count()
}
).ToList();
From SQL Profiler, the Linq generates this SQL query:
exec sp_executesql N'SELECT
[GroupBy1].[K2] AS [PlayerId],
CAST( [GroupBy1].[K1] AS int) AS [C1],
[GroupBy1].[K4] AS [NickName],
[GroupBy1].[K3] AS [UserName],
[GroupBy1].[A1] AS [C2]
FROM ( SELECT
[Extent1].[Seat] AS [K1],
[Extent2].[PlayerId] AS [K2],
[Extent2].[UserName] AS [K3],
[Extent2].[NickName] AS [K4],
COUNT(1) AS [A1]
FROM [dbo].[tbl_PlayerTableSeat] AS [Extent1]
INNER JOIN [dbo].[tbl_Player] AS [Extent2] ON [Extent1].[PlayerId] = [Extent2].[PlayerId]
INNER JOIN [dbo].[tbl_GameVirtualTable] AS [Extent3] ON [Extent1].[GameVirtualTableId] = [Extent3].[GameVirtualTableId]
LEFT OUTER JOIN [dbo].[tbl_PlayerTableWinning] AS [Extent4] ON ([Extent1].[PlayerId] = [Extent4].[PlayerId]) AND ([Extent3].[GameTableId] = [Extent4].[GameTableId])
WHERE [Extent1].[GameVirtualTableId] = #p__linq__0
GROUP BY [Extent1].[Seat], [Extent2].[PlayerId], [Extent2].[UserName], [Extent2].[NickName]
) AS [GroupBy1]',N'#p__linq__0 int',#p__linq__0=36
I want to change COUNT(1) AS [A1] to COUNT([Extent4].[PlayerId]) AS [A1]
so it can return correct data.
I have no idea how to change the LinQ
Trophy = grp.Count()
so that it can count PlayerId of PlayerTableWinning instead of COUNT(1)
Updated: #Ivan Stoev
By adding the g into the group.
group new { p, s, g }
And sum the group
Trophy = grp.Sum(item => item.w != null ? 1 : 0)
It return the correct answer. However, it is using SUM instead of count. The SQL query generated is as below:
exec sp_executesql N'SELECT
[GroupBy1].[K2] AS [PlayerId],
CAST( [GroupBy1].[K1] AS int) AS [C1],
[GroupBy1].[K4] AS [NickName],
[GroupBy1].[K3] AS [UserName],
[GroupBy1].[A1] AS [C2]
FROM ( SELECT
[Filter1].[K1] AS [K1],
[Filter1].[K2] AS [K2],
[Filter1].[K3] AS [K3],
[Filter1].[K4] AS [K4],
SUM([Filter1].[A1]) AS [A1]
FROM ( SELECT
[Extent1].[Seat] AS [K1],
[Extent2].[PlayerId] AS [K2],
[Extent2].[UserName] AS [K3],
[Extent2].[NickName] AS [K4],
CASE WHEN ( NOT (([Extent4].[GameTableId] IS NULL) AND ([Extent4].[PlayerId] IS NULL) AND ([Extent4].[GameRoundId] IS NULL))) THEN 1 ELSE 0 END AS [A1]
FROM [dbo].[tbl_PlayerTableSeat] AS [Extent1]
INNER JOIN [dbo].[tbl_Player] AS [Extent2] ON [Extent1].[PlayerId] = [Extent2].[PlayerId]
INNER JOIN [dbo].[tbl_GameVirtualTable] AS [Extent3] ON [Extent1].[GameVirtualTableId] = [Extent3].[GameVirtualTableId]
LEFT OUTER JOIN [dbo].[tbl_PlayerTableWinning] AS [Extent4] ON ([Extent1].[PlayerId] = [Extent4].[PlayerId]) AND ([Extent3].[GameTableId] = [Extent4].[GameTableId])
WHERE [Extent1].[GameVirtualTableId] = #p__linq__0
) AS [Filter1]
GROUP BY [K1], [K2], [K3], [K4]
) AS [GroupBy1]',N'#p__linq__0 int',#p__linq__0=36

The only (but significant) difference between SQL COUNT(field) and COUNT(1) is that the former is excluding the NULL values, which when applied to the normally required field from the right side of a left outer join like in your case produces a different result when there are no matching records - the former returns 0 while the latter returns 1.
The "natural" LINQ equivalent would be Count(field != null), but that unfortunately is translated to a quite different SQL by the current EF query provider. So in such cases I personally use the closer equivalent expression Sum(field != null ? 1 : 0) which produces a much better SQL.
In order to apply the above to your query, you'll need an access to w inside the grouping, so change
group new { p, s }
to
group new { p, s, w }
and then use
Trophy = grp.Sum(item => item.w != null ? 1 : 0)

Creating Linq from SQL with OrderBy and GroupBy

I have the following table structure.
TableA TableB TableC
- MID - PID - PID
- NAME - INIT_DATE - MID
This is the SQL Query that I need to translate into Linq
SELECT TOP 10 TableA.NAME,
COUNT(TableB.INIT_DATE) AS [TOTALCOUNT]
FROM TableC
INNER JOIN TableA ON TableC.MID = TableA.MID
LEFT OUTER JOIN TableB ON TableC.PID = TableB.PID
GROUP BY TableA.NAME
ORDER BY [TOTALCOUNT] DESC
I tried to reproduce the above query with this Linq query:
iqModel = (from tableC in DB.TableC
join tableA in DB.TableA on tableC.MID equals tableA.MID
select new { tableC, tableA } into TM
join tableB in DB.TableB on TM.tableC.PID equals J.PID into TJ
from D in TJ.DefaultIfEmpty()
select new { TM, D } into MD
group MD by MD.TM.tableA.NAME into results
let TOTALCOUNT = results.Select(item=>item.D.INIT_DATE).Count()
orderby TOTALCOUNT descending
select new SelectListItem
{
Text = results.Key.ToString(),
Value = TOTALCOUNT.ToString()
}).Take(10);
But I think I am doing something wrong.
The Output of the LINQ and SQL is not same. I think up to JOIN or GROUPBY it is Correct.
EDIT :-
I have also tried the following Linq query but still it's not working correctly.
var iqModel = (from c in DB.TableC
join a in DB.TableA on c.MID equals a.MID
join b in DB.b on c.PID equals b.PID into b_join
from b in b_join.DefaultIfEmpty()
select new SelectListItem { Text = a.NAME, Value = b.INIT_DATE != null ? b.INIT_DATE.ToString() : string.Empty });
var igModel = iqModel.GroupBy(item => item.Text);
var result = igModel.OrderByDescending(item => item.Select(r => r.Value).Count());
I want to understand what am I doing wrong and how can it be fixed.
I am newbie to LINQ to SQL I think in above LINQ I really made it complicated by adding more select.

I think the difference is caused by the fact that the SQL COUNT(field) function does not include NULL values. There is no direct equivalent construct in LINQ, but it could be simulated with Count(e => e.Field != null) or like this (which seems to produce better SQL):
var query =
(from a in db.TableA
join c in db.TableC on a.MID equals c.MID
join b in db.TableB on c.PID equals b.PID into joinB
from b in joinB.DefaultIfEmpty()
group b by a.Name into g
let TOTALCOUNT = g.Sum(e => e.INIT_DATE != null ? 1 : 0)
orderby TOTALCOUNT descending
select new SelectListItem { Text = g.Key, Value = TOTALCOUNT }
).Take(10);
which generates the following SQL
SELECT TOP (10)
[Project1].[C2] AS [C1],
[Project1].[Name] AS [Name],
[Project1].[C1] AS [C2]
FROM ( SELECT
[GroupBy1].[A1] AS [C1],
[GroupBy1].[K1] AS [Name],
1 AS [C2]
FROM ( SELECT
[Join2].[K1] AS [K1],
SUM([Join2].[A1]) AS [A1]
FROM ( SELECT
[Extent1].[Name] AS [K1],
CASE WHEN ([Extent3].[INIT_DATE] IS NOT NULL) THEN 1 ELSE 0 END AS [A1]
FROM [dbo].[TableAs] AS [Extent1]
INNER JOIN [dbo].[TableCs] AS [Extent2] ON [Extent1].[MID] = [Extent2].[MID]
LEFT OUTER JOIN [dbo].[TableBs] AS [Extent3] ON [Extent2].[PID] = [Extent3].[PID]
) AS [Join2]
GROUP BY [K1]
) AS [GroupBy1]
) AS [Project1]
ORDER BY [Project1].[C1] DESC

I assume, that you not see "group by" command at resulting query, instead of it "distinct" command is used. Am I right?
First query makes distinct by TableA.NAME and then calculates COUNT(TableB.INIT_DATE) with the help of subquery like this:
select distinct1.Name, (select count() from *join query* where Name = distinct1.Name)
from (select distinct Name from *join query*) as distinct1
If so, not worry about it. Because conversion from linq to real t-sql script sometimes very unpredictable (you can not force them to be equal, only when query is very simple), but both queries are equivalent one to another and return same results (compare them to make sure).

Optimising LINQ-to-SQL queries

I have a very heavy LINQ-to-SQL query, which does a number of joins onto different tables to return an anonymous type. The problem is, if the amount of rows returned is fairly large (> 200), then the query becomes awfully slow and ends up timing out. I know I can increase the data context timeout setting, but that's a last resort.
I'm just wondering if my query would work better if I split it up, and do my comparisons as LINQ-to-Objects queries so I can possibly even use PLINQ to maximise the the processing power. But I'm that's a foreign concept to me, and I can't get my head around on how I would split it up. Can anyone offer any advice? I'm not asking for the code to be written for me, just some general guidance on how I could improve this would be great.
Note I've ensured the database has all the correct keys that I'm joining on, and I've ensured these keys are up to date.
The query is below:
var cons = (from c in dc.Consignments
join p in dc.PODs on c.IntConNo equals p.Consignment into pg
join d in dc.Depots on c.DeliveryDepot equals d.Letter
join sl in dc.Accounts on c.Customer equals sl.LegacyID
join ss in dc.Accounts on sl.InvoiceAccount equals ss.LegacyID
join su in dc.Accounts on c.Subcontractor equals su.Name into sug
join sub in dc.Accountsubbies on ss.ID equals sub.AccountID into subg
where (sug.FirstOrDefault() == null
|| sug.FirstOrDefault().Customer == false)
select new
{
ID = c.ID,
IntConNo = c.IntConNo,
LegacyID = c.LegacyID,
PODs = pg.DefaultIfEmpty(),
TripNumber = c.TripNumber,
DropSequence = c.DropSequence,
TripDate = c.TripDate,
Depot = d.Name,
CustomerName = c.Customer,
CustomerReference = c.CustomerReference,
DeliveryName = c.DeliveryName,
DeliveryTown = c.DeliveryTown,
DeliveryPostcode = c.DeliveryPostcode,
VehicleText = c.VehicleReg + c.Subcontractor,
SubbieID = sug.DefaultIfEmpty().FirstOrDefault().ID.ToString(),
SubbieList = subg.DefaultIfEmpty(),
ScanType = ss.PODScanning == null ? 0 : ss.PODScanning
});
Here's the generated SQL as requested:
{SELECT [t0].[ID], [t0].[IntConNo], [t0].[LegacyID], [t6].[test], [t6].[ID] AS [ID2], [t6].[Consignment], [t6].[Status], [t6].[NTConsignment], [t6].[CustomerRef], [t6].[Timestamp], [t6].[SignedBy], [t6].[Clause], [t6].[BarcodeNumber], [t6].[MainRef], [t6].[Notes], [t6].[ConsignmentRef], [t6].[PODedBy], (
SELECT COUNT(*)
FROM (
SELECT NULL AS [EMPTY]
) AS [t10]
LEFT OUTER JOIN (
SELECT NULL AS [EMPTY]
FROM [dbo].[PODs] AS [t11]
WHERE [t0].[IntConNo] = [t11].[Consignment]
) AS [t12] ON 1=1
) AS [value], [t0].[TripNumber], [t0].[DropSequence], [t0].[TripDate], [t1].[Name] AS [Depot], [t0].[Customer] AS [CustomerName], [t0].[CustomerReference], [t0].[DeliveryName], [t0].[DeliveryTown], [t0].[DeliveryPostcode], [t0].[VehicleReg] + [t0].[Subcontractor] AS [VehicleText], CONVERT(NVarChar,(
SELECT [t16].[ID]
FROM (
SELECT TOP (1) [t15].[ID]
FROM (
SELECT NULL AS [EMPTY]
) AS [t13]
LEFT OUTER JOIN (
SELECT [t14].[ID]
FROM [dbo].[Account] AS [t14]
WHERE [t0].[Subcontractor] = [t14].[Name]
) AS [t15] ON 1=1
ORDER BY [t15].[ID]
) AS [t16]
)) AS [SubbieID],
(CASE
WHEN [t3].[PODScanning] IS NULL THEN #p0
ELSE [t3].[PODScanning]
END) AS [ScanType], [t3].[ID] AS [ID3]
FROM [dbo].[Consignments] AS [t0]
INNER JOIN [dbo].[Depots] AS [t1] ON [t0].[DeliveryDepot] = [t1].[Letter]
INNER JOIN [dbo].[Account] AS [t2] ON [t0].[Customer] = [t2].[LegacyID]
INNER JOIN [dbo].[Account] AS [t3] ON [t2].[InvoiceAccount] = [t3].[LegacyID]
LEFT OUTER JOIN ((
SELECT NULL AS [EMPTY]
) AS [t4]
LEFT OUTER JOIN (
SELECT 1 AS [test], [t5].[ID], [t5].[Consignment], [t5].[Status], [t5].[NTConsignment], [t5].[CustomerRef], [t5].[Timestamp], [t5].[SignedBy], [t5].[Clause], [t5].[BarcodeNumber], [t5].[MainRef], [t5].[Notes], [t5].[ConsignmentRef], [t5].[PODedBy]
FROM [dbo].[PODs] AS [t5]
) AS [t6] ON 1=1 ) ON [t0].[IntConNo] = [t6].[Consignment]
WHERE ((NOT (EXISTS(
SELECT TOP (1) NULL AS [EMPTY]
FROM [dbo].[Account] AS [t7]
WHERE [t0].[Subcontractor] = [t7].[Name]
ORDER BY [t7].[ID]
))) OR (NOT (((
SELECT [t9].[Customer]
FROM (
SELECT TOP (1) [t8].[Customer]
FROM [dbo].[Account] AS [t8]
WHERE [t0].[Subcontractor] = [t8].[Name]
ORDER BY [t8].[ID]
) AS [t9]
)) = 1))) AND ([t2].[Customer] = 1) AND ([t3].[Customer] = 1)
ORDER BY [t0].[ID], [t1].[ID], [t2].[ID], [t3].[ID], [t6].[ID]
}

Try moving the subcontractor join up higher and push the where clause along with it. That way you're not unnecessarily making joins which would fail at the end.
I would also modify the select for the subcontractor id, so you don't get the Id of a potentially null value.
var cons = (from c in dc.Consignments
join su in dc.Accounts on c.Subcontractor equals su.Name into sug
where (sug.FirstOrDefault() == null || sug.FirstOrDefault().Customer == false)
join p in dc.PODs on c.IntConNo equals p.Consignment into pg
join d in dc.Depots on c.DeliveryDepot equals d.Letter
join sl in dc.Accounts on c.Customer equals sl.LegacyID
join ss in dc.Accounts on sl.InvoiceAccount equals ss.LegacyID
join sub in dc.Accountsubbies on ss.ID equals sub.AccountID into subg
let firstSubContractor = sug.DefaultIfEmpty().FirstOrDefault()
select new
{
ID = c.ID,
IntConNo = c.IntConNo,
LegacyID = c.LegacyID,
PODs = pg.DefaultIfEmpty(),
TripNumber = c.TripNumber,
DropSequence = c.DropSequence,
TripDate = c.TripDate,
Depot = d.Name,
CustomerName = c.Customer,
CustomerReference = c.CustomerReference,
DeliveryName = c.DeliveryName,
DeliveryTown = c.DeliveryTown,
DeliveryPostcode = c.DeliveryPostcode,
VehicleText = c.VehicleReg + c.Subcontractor,
SubbieID = firstSubContractor == null ? "" : firstSubContractor.ID.ToString(),
SubbieList = subg.DefaultIfEmpty(),
ScanType = ss.PODScanning == null ? 0 : ss.PODScanning
});

Linq Combine Left Join Data

Say I have the following database:
Users
-------
UserId (PK)
UserName
Roles
-----
RoleId (PK)
RoleName
UserRoles
---------
UserId (PK)
RoleId (PK)
Users 1-M UserRoles M-1 Roles
Using LinqToSQL, I want to return the following set:
[User1], [Role1, Role2, Role3]
[User2], [Role2, Role3]
[User3], []
Etc...
What is the most efficient way to create this LinqToSql Query?
In addition, if I want to create a filter to return only users that have Role1, what would that entail?
Thx.

Define "efficient". But otherwise...
from u in dataContext.Users
select new { User = u, Roles = u.UserRoles.Select(ur => ur.Role) }
And filtering users by RoleID:
from u in dataContext.Users
where u.UserRoles.Any(ur => ur.RoleID == 1)
select u
Or by some other Role attribute, say, Name:
from u in dataContext.Users
where u.UserRoles.Any(ur => ur.Role.Name == "Role 1")
select u
Combining it all together:
from u in dataContext.Users
select new
{
User = u,
Roles = from ur in u.UserRoles
where ur.RoleID == 1 || ur.Role.Name == "Role 1"
select ur.Role
}

This is the single query that I would construct to get your desired result set all at once
from u in Users
join ur in UserRoles on u.UserId equals ur.UserId
join r in Roles on ur.RoleId equals r.RoleId
group r by u into grouping
select grouping
It produces the following SQL:
SELECT [t0].[UserId], [t0].[Username]
FROM [Users] AS [t0]
INNER JOIN [UserRoles] AS [t1] ON [t0].[UserId] = [t1].[UserId]
INNER JOIN [Roles] AS [t2] ON [t1].[RoleId] = [t2].[RoleId]
GROUP BY [t0].[UserID], [t0].[Username]
GO
-- Region Parameters
DECLARE #x1 Int = 2
-- EndRegion
SELECT [t2].[RoleId], [t2].[RoleName]
FROM [Users] AS [t0]
INNER JOIN [UserRoles] AS [t1] ON [t0].[UserId] = [t1].[UserId]
INNER JOIN [Roles] AS [t2] ON [t1].[RoleId] = [t2].[RoleId]
WHERE #x1 = [t0].[UserId]
#Pavel's looks like it produces a better SQL statement:
SELECT [t0].[UserId], [t0].[Username], [t2].[RoleId], [t2].[RoleName] (
SELECT COUNT(*)
FROM [UserRoles] AS [t3]
INNER JOIN [Roles] AS [t4] ON [t4].[RoleId] = [t3].[RoleId]
WHERE [t3].[UserId] = [t0].[UserId]
) AS [value]
FROM [Users] AS [t0]
LEFT OUTER JOIN ([UserRoles] AS [t1]
INNER JOIN [Roles] AS [t2] ON [t2].[RoleId] = [t1].[RoleId]) ON [t1].[UserId] = [t0].[UserId]
ORDER BY [t0].[UserId], [t1].[UserRoleId], [t2].[RoleId]
In terms of efficient, testing is going to be the best way to figure out what most performant approach is for your situation.

How to limit a LINQ left outer join to one row

I have a left outer join (below) returning results as expected. I need to limit the results from the 'right' table to the 'first' hit. Can I do that somehow? Currently, I get a result for every record in both tables, I only want to see one result from the table on the left (items) no matter how many results I have in the right table (photos).
var query = from i in db.items
join p in db.photos
on i.id equals p.item_id into tempPhoto
from tp in tempPhoto.DefaultIfEmpty()
orderby i.date descending
select new
{
itemName = i.name,
itemID = i.id,
id = i.id,
photoID = tp.PhotoID.ToString()
};
GridView1.DataSource = query;
GridView1.DataBind();

This will do the job for you.
from i in db.items
let p = db.photos.Where(p2 => i.id == p2.item_id).FirstOrDefault()
orderby i.date descending
select new
{
itemName = i.name,
itemID = i.id,
id = i.id,
photoID = p == null ? null : p.PhotoID.ToString();
}
I got this sql when I generated it against my own model (and without the name and second id columns in the projection).
SELECT [t0].[Id] AS [Id], CONVERT(NVarChar,(
SELECT [t2].[PhotoId]
FROM (
SELECT TOP (1) [t1].[PhotoId]
FROM [dbo].[Photos] AS [t1]
WHERE [t1].[Item_Id] = ([t0].[Id])
) AS [t2]
)) AS [PhotoId]
FROM [dbo].[Items] AS [t0]
ORDER BY [t0].[Id] DESC
When I asked for the plan, it showed that the subquery is implemented by this join:
<RelOp LogicalOp="Left Outer Join" PhysicalOp="Nested Loops">

What you want to do is group the table. The best way to do this is:
var query = from i in db.items
join p in (from p in db.photos
group p by p.item_id into gp
where gp.Count() > 0
select new { item_id = g.Key, Photo = g.First() })
on i.id equals p.item_id into tempPhoto
from tp in tempPhoto.DefaultIfEmpty()
orderby i.date descending
select new
{
itemName = i.name,
itemID = i.id,
id = i.id,
photoID = tp.Photo.PhotoID.ToString()
};
Edit: This is Amy B speaking. I'm only doing this because Nick asked me to. Nick, please modify or remove this section as you feel is appropriate.
The SQL generated is quite large. The int 0 (to be compared with the count) is passed in via parameter.
SELECT [t0].X AS [id], CONVERT(NVarChar(MAX),(
SELECT [t6].Y
FROM (
SELECT TOP (1) [t5].Y
FROM [dbo].[Photos] AS [t5]
WHERE (([t4].Y IS NULL) AND ([t5].Y IS NULL)) OR (([t4].Y IS NOT NULL) AND ([t5].Y IS NOT NULL) AND ([t4].Y = [t5].Y))
) AS [t6]
)) AS [PhotoId]
FROM [dbo].[Items] AS [t0]
CROSS APPLY ((
SELECT NULL AS [EMPTY]
) AS [t1]
OUTER APPLY (
SELECT [t3].Y
FROM (
SELECT COUNT(*) AS [value], [t2].Y
FROM [dbo].[Photos] AS [t2]
GROUP BY [t2].Y
) AS [t3]
WHERE (([t0].X) = [t3].Y) AND ([t3].[value] > #p0)
) AS [t4])
ORDER BY [t0].Z DESC
The execution plan reveals three left joins. At least one is trivial and should not be counted (it brings in the zero). There is enough complexity here that I cannot clearly point to any problem for efficiency. It might run great.

You could do something like:
var q = from c in
(from s in args
select s).First()
select c;
Around the last part of the query. Not sure if it will work or what kind of wack SQL it will produce :)

Use an inner query. Include DefaultIfEmpty for the case of no photo and orderby for the case of more than one. The following example takes the photo with the greatest id.
var query =
from i in db.items
let p = from p in db.photos where i.id == p.item_id orderby p.id select p).DefaultIfEmpty().Last()
orderby i.date descending
select new {
itemName = i.name,
itemID = i.id,
id = i.id,
photoID = p.PhotoID
};
If you need to handle the case of no photo specially, you can omit DefaultIfEmpty and use FirstOrDefault/LastOrDefault instead.