We Keep Coding

Fast join on Multiple IEnumerable

Whith s_records, q_records, d_records, i_records all of type IEnumerable<MyRecord>, querytwo works just as expected. But what if I want to join multiple IEnumerable on the same equality of the same fields?
var querytwo = from a in s_records
join b in q_records
on a.date equals b.date
select new { s_line = a.line, q_line = b.line };
Console.WriteLine(querytwo.Count());
This query doesn't work I am trying to do the same as in querytwo, but join on multiple IEnumerable<MyRecord>:
var query = from a in s_records
join b in q_records
join c in d_records
join d in i_records
on a.date equals b.date equals c.date equals d.date
select new { s_line = a.line, q_line = b.line, d_line = c.line, i_line = d.line };

Your syntax is to off to some extent. it should be:
var querytwo = from a in s_records
join b in q_records on a.date equals b.date
join c in d_records on b.date equals c.date
join d in i_records on c.date equals d.date
select new {
s_line = a.line,
q_line = b.line,
d_line = c.line,
i_line = d.line
};

How to change query to Entity Framework

I want to change this SQL query to Entity Framework query:
SELECT
dbo.ClassTiming.StartTime,
dbo.ClassTiming.EndTime,
dbo.Employee.StaffName,
dbo.Department.DepartmentName,
dbo.Class.ClassName,
dbo.Section.SectionName,
dbo.WeekDay.DayName
FROM dbo.Timetable
INNER JOIN dbo.ClassTiming
ON dbo.Timetable.ClassTimingId = dbo.ClassTiming.Id
INNER JOIN dbo.Employee
ON dbo.Timetable.StaffId = dbo.Employee.StaffID
INNER JOIN dbo.Department
ON dbo.Timetable.DepartmentId = dbo.Department.id
INNER JOIN dbo.Section
ON dbo.Timetable.SectionID = dbo.Section.ID
INNER JOIN dbo.Class
ON dbo.Timetable.ClassID = dbo.Class.ID
INNER JOIN dbo.WeekDay
ON dbo.Timetable.WeekDayId = dbo.WeekDay.Id

This should work
var db = new YourDbContext();
var result = (from t in db.Timetables
join c in db.ClassTimings on t.ClassTimingId equals c.Id
join e in db.Employees on t.StaffId equals e.StaffID
join d in db.Departments on t.DepartmentId equals d.Id
join s in db.Sections on t.SectionID equals s.Id
join cl in db.Classes on t.ClassID equals cl.Id
join w in db.WeekDays on t.WeekDayId equals w.Id
select
new { c.StartTime,
c.EndTime, e.StaffName,
d.DepartmentName,
cl.ClassName,
s.SectionName,
w.DayName
}
).ToList();

Adding a Condition to a LINQ join

I'm working with the following linq query:
var docList = from c in container.DocumentDeliveryPreferences
join o in container.Documents on c.DocumentId equals o.DocumentId
select new { o.Name, o.DocumentType, c.CustomerId };
How can I modify this to select only Documents where c.CustomerId equals X(some paramenter)?

You could try something the following:
var docList = from c in container.DocumentDeliveryPreferences
join o in container.Documents
on c.DocumentId equals o.DocumentId
where c.CustomerId == X
select new { o.Name, o.DocumentType, c.CustomerId };
where X is your parameter.

LINQ to Entities multiple join

Hi im trying to replicate this mysql query
SELECT a.id, a.title, a.description, a.categories_id, c.name, d.title
FROM ads AS a
INNER JOIN locations AS b
ON a.locations_id = b.id
INNER JOIN areas AS c
ON b.areas_id = c.id
INNER JOIN categories AS d
ON a.categories_id = d.id
WHERE a.title LIKE '%mini%'
AND c.name = 'Fyn'
LIMIT 10
and here is it in LINQ
var query = (from a in db.ads
join b in db.locations on a.locations_id equals b.id
join c in db.areas on b.id equals c.id
join d in db.categories on a.categories_id equals d.id
where a.title.Contains(searchQuery) && c.name.Equals(area)
select new {
a.id,
a.title,
a.description,
category = d.title
}).Take(10);
it doesn't show any error but it's not returning any data.

You have mistake in third line:
join c in db.areas on b.id equals c.id
should be
join c in db.areas on b.areas_id equals c.id

Convert special SQL query to Linq

do you know how write this SQL Query to linq ?
SELECT *
FROM
a
INNER JOIN b
ON a.FkSubmissionId = b.Id
RIGHT JOIN c
ON a.FkItemId = c.Id
WHERE
(b.FkUserId = '...' OR b.FkUserId is null)
and
(c.FkTenderId = 2)
I use Linquer and the best I have from the tool is that :
Linq :
from
items in _context.Items
from
si in _context.si
join s in _context.s
on new { fki = si.fki } equals new { fki = s.Id }
into
submissions_join
from
s in submissions_join.DefaultIfEmpty()
...
Result in SQL :
SELECT *
FROM
[Items] AS [t0]
CROSS JOIN [SubmissionsItems] AS [t1]
LEFT OUTER JOIN [Submissions] AS [t2]
ON [t1].[FkSubmissionId] = [t2].[Id]
WHERE
(([t2].[FkUserId] = #p0) OR (([t2].[FkUserId]) IS NULL))
AND
([t0].[FkTenderId] = #p1)
So the final result it not what I get from the query I need...
Thank you for your help !!!

Try this:
var part1 =
from x in a
join y in b on x.FkSubmissionId equals y.Id
where b.FkUserId = "..."
select new {x, y};
var part2 =
from c in z
where c.FkTenderId == 2
join xy in part1
on z.Id equals xy.x.FkItemId
into xys
from xy in xys.DefaultIfEmpty()
select new {xy.x, xy.y, z};

I would reorder your query so you can use a left join instead of a right join
var query = from c in context.C
from a in context.A.Where(x => c.Id == x.FkItemId)
.DefaultIfEmpty()
join b in context.B on a.FkSubmissionId equals b.id
where b.FkUserId == '...' || b.FkUserId == null
where c.FkTenderId == 2
select new {
a,
b,
c
};