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Linq query for top parents by number of childs, including this number

In my model, there are entities Article and Tag in many-to-many relation through table ArticleTag.
I want to select "trending tags" - tags with most articles in last X days, and I want this count too.
Basically, I need help creating EF Linq query equivalent to this SQL query, with ideal result being Dictionary<Tag, int>
SELECT TOP 50
t.Id, t.Name, count(*)
FROM ArticleTag at
JOIN Article a ON a.Id = at.ArticleId
JOIN Tag t ON t.Id = at.TagId
WHERE a.DateCreated > '2019-10-01'
GROUP BY t.Id, t.Name
ORDER BY count(*) DESC
Can this be done without having ArticleTag as DbSet in DbContext (since it is not really an entity, and I dont need it besides this query).

You have to use navigation properties for this query and do not need to know anything about ArticleTag table.
var query =
from a in ctx.Articles
from t in a.Tags
where a.DateCreated > someDate
group t by new { t.Id, t.Name } into g
orderby g.Count() descending
select new
{
g.Key.Id,
g.Key.Name,
Count = g.Count()
};
var result = query
.Take(50)
.ToDictionary(x => new Tag { Id = x.Id, Name = x.Name }, x => x.Count);

How to write subquery with the any quantifier using linq?

I have a problem with using any in linq I do not know how to do it correctly.
I have to write this in linq:
SELECT ename, job, deptno
FROM emp
WHERE sal > ANY
(
SELECT DISTINCT sal
FROM emp
WHERE deptno = 30
);
I write only this:
var min = (from emp in Emps
where emp.Deptno == 30
select emp.Sal
).Distinct();
var result = (from emp in Emps
where min.Any() > emp.Sal
select new
{
emp.Ename
});

Linq doesn't have an any/some operator in the way Sql Server does.
var salariesInTargetDepartment = Emps
.Where(x => x.Deptno == 30)
.Select(x => x.Sal)
.Distinct()
.ToList(); // the ToList is not required, but seeing you're going to be executing
// against this query many times, it will be better to cache the results.
var matchingEmployees = Emps
.Where(emp => salariesInTargetDepartment
.Any(target => emp.Sal > target)
);
The where clause in the second statement says "Only include this record if this record's Sal property is greater than at least one entry in the salariesInTargetDepartment collection."

Concentrating a join into a single column in linq query

I have the following query:
var query = (from wo in _dbContext.WorkOrder
join opr in _dbContext.Operation
on wo.operationID equals opr.operationID
where wo.orderid == selectedorderid
select new {wo.orderid, wo.workOrderID, wo.itemID, wo.operationID, opr.operationName, wo.operationCode}).ToList();
I also have another table,which joins with workorder table,and returns multiple values.
What I want to do is,I want to join the table and get a single column of it as a concentrated column in my query such as (id1,id2,id3) etc. How can I achieve this?

What about:
var query = (from wo in _dbContext.WorkOrder
join opr in _dbContext.Operation
on wo.operationID equals opr.operationID
where wo.orderid == selectedorderid
select new {wo.orderid, wo.workOrderID, wo.itemID, wo.operationID, opr.operationName, wo.operationCode}).ToList();
var orders = queryGroupBy(i => i.workOrderID)
.Select(i => new {WorkOrderId = i.workOrderID, ConcatinatedIds = String.Join(", ", i.Select(j => j.operationID))})
.ToList();

LINQ: Group by aggregate but still get information from the most recent row?

Let's say I have a table that holds shipping history. I'd like to write a query that counts the amount of shipments per user and gets the shipping name from the most recent entry in the table for that user.
Table structure for simplicity:
ShipmentID
MemberID
ShippingName
ShippingDate
How do I write a LINQ C# query to do this?

It sounds like might want something like:
var query = from shipment in context.ShippingHistory
group shipment by shipment.MemberID into g
select new { Count = g.Count(),
MemberID = g.Key,
MostRecentName = g.OrderByDescending(x => x.ShipmentDate)
.First()
.ShipmentName };

Not really a LINQ answer, but personally, I'd be dropping to SQL for that, to make sure it isn't doing any N+1 etc; for example:
select s1.MemberID, COUNT(1) as [Count],
(select top 1 ShippingName from Shipping s2 where s2.MemberID = s1.MemberID
order by s2.ShippingDate desc) as [LastShippingName]
from Shipping s1
group by s1.MemberID
You can probably do LINQ something like (untested):
var qry = from row in data
group row by row.MemberId into grp
select new {
MemberId = grp.Key,
Count = grp.Count(),
LastShippingName =
grp.OrderByDescending(x => x.ShippingDate).First().ShippingName
};

How to use group by and having count in Linq

I am having trouble trying to convert the following query from SQL to Linq, in particular with the having count and group by parts of the query:
select ProjectID
from ProjectAssociation
where TeamID in ( select TeamID
from [User]
where UserID in (4))
group by ProjectID
having COUNT(TeamID) = (select distinct COUNT(TeamID)
from [User]
where UserID in (4))
Any advice on how to do so would be much appreciated.

var groups = from pa in ProjectAssociation
let teamIds = User.Where(u => u.UserID == 4).Select(u => u.TeamID)
where teamIds.Contains(pa.TeamID)
group pa by pa.ProjectID;
var result = from g in groups
let count = User.Where(u => u.UserID == 4).Select(u => u.TeamID).Distinct().Count()
where g.Count() == count
select g.Key;
Or maybe more optimal:
var teamIds = User.Where(u => u.UserID == 4).Select(u => u.TeamID).AsEnumerable();
var groups = ProjectAssociation.Where(pa => teamIds.Contains(pa.TeamID)
.GroupBy(pa => pa.ProjectID);
var result = from g in groups
let count = teamIds.Distinct().Count()
where g.Count() == count
select g.Key;
By the way, i think that by
select distinct COUNT(TeamID)
you meant:
select COUNT(distinct TeamID)

There is a tool (cheap) that will convert queries like this for you. It's called Linqer. I own a copy and have found that it's able to convert event the most complex of queries. The URL is http://www.sqltolinq.com/
It's not free, but it's pretty inexpensive and has a 30 day trial.