We Keep Coding

LINQ - query on query results (some complex one)

Need some help in writing LINQ from the following SQL.
The main problem is double grouping.
I'm stacked in the second grouping
group by s.[e-year], s.[e-month]
Don't know how to implement.
Thanks a lot.
select s.[e-year], s.[e-month], count(s.projectid) 'projects entranced',
---------------------------------------------
(select count(subquery.CustomerTypeID) from
(select count(ap.ProjectID) as 'count', c.CustomerTypeID FROM Logging_ProjectsEntrances] pe
inner join users u on pe.userid = u.userid
inner join Companies c on u.CompanyId = c.CompanyID
inner join AssignedProjects up on pe.ProjectID = up.ProjectID
inner join Projects p on up.ProjectID = p.ProjectID
where ap.ProductID = 1 and year(pe.EntranceDate) = s.[e-year] and MONTH(pe.entrancedate) = s.[e-month] and c.CustomerTypeID = 2
group by ap.ProjectID, c.CustomerTypeID) subquery
group by subquery.CustomerTypeID
)
--------------------------------------------
from
(
select YEAR(pe.EntranceDate) as 'e-year', MONTH(pe.EntranceDate) as 'e-month', up.ProjectID as 'projectid'
FROM Logging_ProjectsEntrances pe
inner join AssignedProjects ap on pe.ProjectID = ap.ProjectID
inner join Projects p on ap.ProjectID = p.ProjectID
where ap.ProductID = 1
group by year(pe.EntranceDate), month(pe.EntranceDate), ap.ProjectID
) as s
group by s.[e-year], s.[e-month]
order by s.[e-year] desc , s.[e-month] desc

For translating SQL to LINQ query comprehension:
Translate FROM subselects as separately declared variables.
Translate each clause in LINQ clause order, translating monadic operators (DISTINCT, TOP, etc) into functions applied to the whole LINQ query.
Use table aliases as range variables. Use column aliases as anonymous type field names.
Use anonymous types (new { ... }) for multiple columns.
Left Join is simulated by using a into join_variable and doing another from from the join variable followed by .DefaultIfEmpty().
Replace COALESCE with the conditional operator and a null test.
Translate IN to .Contains() and NOT IN to !...Contains()
SELECT * must be replaced with select range_variable or for joins, an anonymous object containing all the range variables.
SELECT fields must be replaced with select new { ... } creating an anonymous object with all the desired fields or expressions.
Proper FULL OUTER JOIN must be handled with an extension method.
Note: Your SQL query is using a SQL trick (SELECT x ... GROUP BY x) to perform the equivalent of a DISTINCT, which should be used as it expresses the intent more clearly.
So, for your SQL query:
var subq = (from pe in projectsEntrances
join ap in assignedProjects on pe.ProjectID equals ap.ProjectID
join p in projects on ap.ProjectID equals p.ProjectID
where ap.ProductID == 1
select new { e_year = pe.EntranceDate.Year, e_month = pe.EntranceDate.Month, ap.ProjectID }).Distinct();
var ans = from s in subq
group s by new { s.e_year, s.e_month } into sg
orderby sg.Key.e_year descending, sg.Key.e_month descending
select new { sg.Key.e_year, sg.Key.e_month, ProjectsEntranced = sg.Count() };

LINQ Left and Right Join Query

This is my sql query, how can I generate this query into LINQ:
SELECT
TimeTable.StartTime,
sum(Booking.Quantity) as Total
FROM PromotionSlot
RIGHT JOIN TimeTable
ON PromotionSlot.StartHour = TimeTable.StartTime
LEFT JOIN Booking
ON PromotionSlot.ID = Booking.PromotionSlotID
GROUP BY TimeTable.StartTime
Result:
|StartTime |Total|
---------------------
9 NULL
10 NULL
11 2
12 2
13 NULL
14 NULL
15 NULL
16 NULL
17 NULL
18 NULL
19 NULL
20 NULL
21 NULL
This is what I attempted, I'm not sure that the structure of the linq is correct with my SQL query. But I faced error about The cast to value type 'Int32' failed because the materialized value is null. Either the result type's generic parameter or the query must use a nullable type. Please guide me, thank you all in advance!
var bookingdata =
(from ps in dc.PromotionSlots
join t in dc.TimeTables on ps.StartHour equals t.StartTime into Ts
join bo in dc.Bookings on ps.ID equals bo.PromotionSlotID into Bs
from time in Ts.DefaultIfEmpty()
from book in Bs.DefaultIfEmpty()
group new {time,book} by time.StartTime into NewGroup
select new dataView
{
StartTime = NewGroup.Key,
numBookings = NewGroup.Select(a => a.book!=null? a.book.Quantity: 0).Sum()
}).ToList();
Here is my dataView model
public class dataView
{
public int? StartTime { get; set; }
public int? numBookings { get; set; }
}
UPDATED:
changed StartTime in my dataView model to int? and this is the result by using console.log()
Format: #:console.log("* " + "#item.StartTime" + ":" + "#item.numBookings");
* :0
* 10:0
* 11:2
* 12:2
I found out the reason why the above console.log() will appear this result. I tried to change my SQL Query RIGHT JOIN TimeTable to LEFT JOIN TimeTable. The return result totally the same like the output from my LINQ.

I think the problem you're hitting is that in ad-hoc query results, any column value can be null (eg., the Total column in your results example has mixed values, int and null). But C# is not so lenient, an a null value cannot be stuffed into a integer value.
I think that in your dataView type, the numBookings property is probably set to int, and an int type in C# is not nullable.
I believe if you change it to a nullable int, like:
public int? numBookings { get; set; }
then that may fix your error. If not that, then the following might work:
numBookings = NewGroup.Select(a => a.book!=null ? (a.book.Quantity ?? 0): 0).Sum() ?? 0
But I am not sure about this last one.
UPDATE
What if you update your LINQ query to use LEFT JOIN for both joins, like so:
var bookingdata = (
from t in dc.TimeTables
join ps in dc.PromotionSlots on t.StartTime equals ps.StartHour into Ts
from time in Ts.DefaultIfEmpty()
join bo in dc.Bookings on time.ID equals bo.PromotionSlotID into Bs
from book in Bs.DefaultIfEmpty()
group new {time, book} by time.StartTime into NewGroup
select new dataView
{
StartTime = NewGroup.Key,
numBookings = NewGroup.Select(a => a.book!=null? a.book.Quantity: 0).Sum()
}
).ToList();
Does this make the results more consistent with the SQL query?

How to retrieve all columns from table1 and matching columns from table2(Left outer join) using Linq

I have to retrieve all the columns from table1 and matching columns from table2. I have a stored procedure as :
alter Procedure [dbo].[usp_Property]
#UserId bigint =null
As
Begin
select P.PID, P.PropertyName, P.SBUArea, P.ListedOn,
P.Availability, P.Price, F.UserID, F.PID as FavProjId
from dbo.Property P left outer join dbo.Favorite F
on (F.PID=P.PID And F.UserID=#UserId)
I want to get Linq query for the same. So far I tried with something like
//User Id comes from session..
//var userId
var result=(from p in Properties
join f in Favorites
on p.PID equals f.PID into r
from r1 in r.DefaultIfEmpty()
where r1.UserID==userId
select new
{
p.PID,
p.PropertyName,
p.SBUArea, p.ListedOn,
r1.UserId
});
Can anyone please correct me. I want to use left outer join or any other alternate thing here.

If I beautify your SP's code, I get this:
DECLARE #UserId int
SET #UserId = 12435
SELECT
P.PID
,P.PropertyName
,P.SBUArea
,P.ListedOn
,P.Availability
,P.Price
,F.UserID
,F.PID AS FavProjId
FROM Property AS P
LEFT JOIN Favorite AS F
ON (F.PID=P.PID AND F.UserID = #UserId)
Now I wonder if you need that UserId in the WHERE clause of the SQL, or really in the join.
But anyway, here the LINQ-equivalent of exactly that SQL:
System.Int64 __UserId = 12435;
var query = (
from P in Repo.Property
from F in Repo.Favorite
.Where(fav=> fav.PID == P.PID && fav.UserID == __UserId)
.DefaultIfEmpty() // <== makes join left join
select new
{
PID = P.PID
,PropertyName = P.PropertyName
,SBUArea = P.SBUArea
,ListenOn = P.ListedOn
,Availabiity = P.Availability
,Price = P.Price
,UserId = F.UserID
,FavProjId = F.PID
}
);
var data = (query).ToList();

Use anonymous objects in your selection
var result = from t in table1
join x in table2
on t.id equals x.id
select new { id = t.id, col1 = t.col1, col2 = x.col2 }

If you will put the where clause after join you may get null reference exception because DefaultIfEmpty returns default value for non matching rows. You can filter the records before joining itself like this:-
var result=(from p in Properties
join f in Favorites.Where(x => x.UserID == userId)
on p.PID equals f.PID into r
from r1 in r.DefaultIfEmpty()
select new
{
p.PID,
p.PropertyName,
p.SBUArea,
p.ListedOn,
r1.UserId
});
Please note you need to access properties of Favorites using r1.
Update:
As far as I have understood you need all records from Property table and only matching rows from Favorite table. But you have a filter on your Favorite table so the ultimate data source will differ. Let me make my point clear by this example:-
Suppose you have following data in Property table:-
PID PropertyName Availability Price
1 aaa true 20
2 bbb false 10
3 ccc true 50
4 ddd false 80
5 eee true 55
6 fff false 70
and Favorite table like this:-
FID PID UserId
1 4 1001
2 2 1005
3 5 1007
And let's say you want all records for UserId 1005, then the result should contain all the property Id's from 1 till 6 even if UserId 1005 doesn't match for property Id's 4 & 2 right? So the query above is as per this understanding. Check this Fiddle with same example and output.

left join in Linq query

I'm trying to do a left join, not an inner join in a linq query. I have found answers related to using DefaultIfEmpty() however I can't seem to make it work. The following is the linq query:
from a in dc.Table1
join e in dc.Table2 on a.Table1_id equals e.Table2_id
where a.Table1_id == id
orderby a.sort descending
group e by new
{
a.Field1,
a.Field2
} into ga
select new MyObject
{
field1= ga.Key.Field1,
field2= ga.Key.Field2,
manySubObjects = (from g in ga select new SubObject{
fielda= g.fielda,
fieldb= g.fieldb
}).ToList()
}).ToList();
The query only gives me the rows from table 1 that have a corresponding record in table 2. I would like every record in table 1 populated into MyObject and a list of 0-n corresponding records listed in manySubObjects for each MyObject.
UPDATE:
I tried the answer to the question that is a "possible duplicate", mentioned below. I now have the following code that does give me one record for each item in Table1 even if there is no Table2 record.
from a in dc.Table1
join e in dc.Table2 on a.Table1_id equals e.Table2_id into j1
from j2 in j1.DefaultIfEmpty()
where a.Table1_id == id
orderby a.sort descending
group j2 by new
{
a.Field1,
a.Field2
} into ga
select new MyObject
{
field1= ga.Key.Field1,
field2= ga.Key.Field2,
manySubObjects = (from g in ga select new SubObject{
fielda= g.fielda,
fieldb= g.fieldb
}).ToList()
}).ToList();
However, with this code, when there is no record in table2 I get "manySubObject" as a list with one "SubObject" in it with all null values for the properties of "SubObject". What I really want is "manySubObjects" to be null if there is no values in table2.

In reply to your update, to create the null listing, you can do a ternary in your assignment of manySubObjects.
select new MyObject
{
field1= ga.Key.Field1,
field2= ga.Key.Field2,
manySubObjects =
(from g in ga select g).FirstOrDefaut() == null ? null :
(from g in ga select new SubObject {
fielda= g.fielda,
fieldb= g.fieldb
}).ToList()
}).ToList();
Here is a dotnetfiddle that tries to do what you're attempting. https://dotnetfiddle.net/kGJVjE
Here is a subsequent dotnetfiddle based on your comments. https://dotnetfiddle.net/h2xd9O
In reply to your comments, the above works with Linq to Objects but NOT with Linq to SQL. Linq to SQL will complain that it, "Could not translate expression ... into SQL and could not treat as a local expression." That's because Linq cannot translate the custom new SubObject constructor into SQL. To do that, you have to write more code to support translation into SQL. See Custom Method in LINQ to SQL query and this article.
I think we've sufficiently answered your original question about left joins. Consider asking a new question about using custom methods/constructors in Linq to SQL queries.

I think the desired Result that you want can be given by using GroupJoin()
The code Below will produce a structure like so
Field1, Field2, List < SubObject > null if empty
Sample code
var query = dc.Table1.Where(x => Table1_id == id).OrderBy(x => x.sort)
.GroupJoin(dc.Table2, (table1 => table1.Table1_id), (table2 => table2.Table2_id),
(table1, table2) => new MyObject
{
field1 = table1.Field1,
field2 = table1.Field2,
manySubObjects = (table2.Count() > 0)
? (from t in table2 select new SubObject { fielda = t.fielda, fieldb = t.fieldb}).ToList()
: null
}).ToList();
Dotnetfiddle link
UPDATE
From your comment I saw this
ga.Select(g = > new SubObject(){fielda = g.fielda, fieldb = g.fieldb})
I think it should be (depends on how "ga" is built)
ga.Select(g => new SubObject {fielda = g.fielda, fieldb = g.fieldb})
Please update your question with the whole query, it will help solve the issue.
** UPDATE BIS **
sentEmails = //ga.Count() < 1 ? null :
//(from g in ga select g).FirstOrDefault() == null ? null :
(from g in ga select new Email{
email_to = g.email_to,
email_from = g.email_from,
email_cc = g.email_cc,
email_bcc = g.email_bcc,
email_subject = g.email_subject,
email_body = g.email_body }).ToList()
Should be:
sentEmails = //ga.Count() < 1 ? null :
((from g in ga select g).FirstOrDefault() == null) ? null :
(from g in ga select new Email{
email_to = g.email_to,
email_from = g.email_from,
email_cc = g.email_cc,
email_bcc = g.email_bcc,
email_subject = g.email_subject,
email_body = g.email_body }).ToList()
Checks if the group has a First, if it doesn't the group doesn't have any records so the Action.Name for a Time Stamp has no emails to send. If the First isn't null the loop throw the group elements and create a list of Email,

var results =
(
// Use from, from like so for the left join:
from a in dc.Table1
from e in dc.Table2
// Join condition goes here
.Where(a.Id == e.Id)
// This is for the left join
.DefaultIfEmpty()
// Non-join conditions here
where a.Id == id
// Then group
group by new
{
a.Field1,
a.Field2
}
).Select(g =>
// Sort items within groups
g.OrderBy(item => item.sortField)
// Project required data only from each item
.Select(item => new
{
item.FieldA,
item.FieldB
}))
// Bring into memory
.ToList();
Then project in-memory to your non-EF-model type.

Left Join in Linq and using the variable for other joins

I am stuck with the error "value cannot be null. parameter name row" when I use Left join in Linq for DataSet.
Following is the data and the linq query.
DataRowCollection - items (Columns - Item_id, SKU, Quantity)
DataRowCollection - promotions (Columns - Item_id, Promotion_Id)
DataRowCollection - components (Columns - Component_id, Promotion_id)
DataRowCollection - amounts (Columns - Component_id, Amount_Text, currency)
var q =
from Item in items
join promotion in promotions
on Item.Field<int>("Item_id") equals promotion.Field<int?>("Item_id") into promo
from promotion in promo.DefaultIfEmpty()
join disccomponent in components
on promotion.Field<int>("Promotion_Id") equals disccomponent.Field<int?>("Promotion_Id")
join discamounts in amounts
on disccomponent.Field<int>("Component_id") equals discamounts.Field<int?>("Component_id")
where disccomponent.Field<string>("Type") == "Principal"
select new
{
SKU = Item.Field<string>("SKU"),
Quantity = Item.Field<string>("Quantity"),
DiscountAmount = discamounts.Field<string>("Amount_Text"),
DiscountCurrency = discamounts.Field<string>("currency")
};
I need to get the following:
SKU, Qty and Discount details for items which have discount
SKU, Qty for items which do not have any discount
The code worked without left outer join when all items had discount, but if any item does not have any discount it skips that item and hence I had to use the left outer join.
Any help is highly appreciated. Please let me know if any clarification is needed.
Thanks in advance.

I think you are trying to access properties on a null discamounts. Perhaps your select new should look something like this...
select new
{
SKU = Item.Field<string>("SKU"),
Quantity = Item.Field<string>("Quantity"),
DiscountAmount = discamounts == null ? "" : discamounts.Field<string>("Amount_Text"),
DiscountCurrency = discamounts == null ? "" : discamounts.Field<string>("currency")
};

Give your join a name by using into and use DefaultIfEmpty on it. Something like this (look at the last join and from expression in the statement)
var q =
from Item in items
join promotion in promotions
on Item.Field<int>("Item_id") equals promotion.Field<int?>("Item_id") into promo
from promotion in promo.DefaultIfEmpty()
join disccomponent in components
on promotion.Field<int>("Promotion_Id") equals disccomponent.Field<int?>("Promotion_Id")
join discamounts in amounts
on disccomponent.Field<int>("Component_id") equals discamounts.Field<int?>("Component_id") into DiscamountJoin
from discamount in DiscamountJoin.DefaultIfEmpty()
where disccomponent.Field<string>("Type") == "Principal"
select new
{
SKU = Item.Field<string>("SKU"),
Quantity = Item.Field<string>("Quantity"),
DiscountAmount = discamount.Field<string>("Amount_Text"),
DiscountCurrency = discamount.Field<string>("currency")
};

Thanks everyone for your help. I made this work by splitting it into 2 different linq queries below.
The first query gets the promotion data in a var
var promoData =
from promotion in promotions
join component in components
on promotion.Field<int>("Promotion_Id") equals component.Field<int?>("Promotion_Id")
join amount in amounts
on component.Field<int>("Component_id") equals amount.Field<int?>("Component_id")
where component.Field<string>("Type") == "Principal"
select new
{
Item_id = promotion.Field<int?>("Item_id"),
Promotion_id = promotion.Field<int>("Promotion_Id"),
DiscountAmount = amount == null ? "" : amount.Field<string>("Amount_Text"),
DiscountCurrency = amount == null ? "" : amount.Field<string>("currency")
};
The second query uses the promotions var to simplify the query and get the resuls
var q =
from Item in items
join promotion in promoData
on Item.Field<int>("Item_id") equals promotion.Item_id into promo
from promoJoin in promo.DefaultIfEmpty()
select new
{
SKU = Item.Field<string>("SKU"),
Quantity = Item.Field<string>("Quantity"),
DiscountAmount = promoJoin != null ? promoJoin.DiscountAmount : "0",
DiscountCurrency = promoJoin != null ? promoJoin.DiscountCurrency : ""
};
This approach works perfectly and I get all the items whether they have promotions or not. I am still thinking whether doing the same was possible in a single query :)
For now marking this as an answer, if anyone comes up with some other better way will mark that.