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Add 'where' clausures dynamically to linq query

I have this linq query:
var query = (from dc in context.Table1.Include(d => d.Doc)
join u in _context.Table2 on dc.IDDoc equals u.IDDoc
where dc.ID == id && u.IDUser == user.IDUser
select dc)
.Union(from dc in context.Table1.Include(d => d.Doc)
join p in _context.Table3 on dc.IDDoc equals p.IDDoc
where dc.ID == id
select dc);
And I want to add more where conditions dynamically depends of a list (List ids)
What I want to achieve is something like this:
Imagine that I have a List ids = new(){1, 2, 5, 27);
What I want to do is to add that info into this part of the query to have something like this:
.Union(from dc in context.Table1.Include(d => d.Doc)
join p in _context.Table3 on dc.IDDoc equals p.IDDoc
where dc.ID == id && p.ID == 1 || p.ID == 2 || p.ID == 5 || p.ID = 27
select dc)
But if next time list is List ids = new(){4}, query should look like:
.Union(from dc in context.Table1.Include(d => d.Doc)
join p in _context.Table3 on dc.IDDoc equals p.IDDoc
where dc.ID == id && p.ID == 4
select dc)
Is it even possible? If not, what would be a possible solution?
Thank you
EDIT: I made up with this query because I have no clue about how to add it to my main query.
What I really have is this:
var mainQuery = _context.RootTable
.Include(i => i.Items).ThenInclude(dc => dc.Docs)
.Include(i => i.Items).ThenInclude(sg => sg.Signs)
.FirstOrDefault(m => m.ID== id);
And what I want to do is to filter the ".ThenInclude(dc => dc.Docs) with the other query. I can't figure out how to do it in a better and efficient way that with two sepparate queries.

Use Enumerable.Contains:
List<int> ids = new(){4};
....
.Union(from dc in context.Table1.Include(d => d.Doc)
join p in _context.Table3 on dc.IDDoc equals p.IDDoc
where dc.ID == id && ids.Contains(p.ID) // here
select dc)
....

How to groupby with inner join using linq lamba expression

I'm trying to convert a sql stored proc to linq. I'm having issues with the groupby and inner joins.
Here is what I've tried:
var r = _context.Table1
.GroupBy(x => new { x.OptionId, x.Years, x.Strike })
.Join(_context.Table2,
oc => oc.OptionId, o => o.OptionId, (oc, o) => new
{
OptionsCosts = oc,
Options = o
}).Where(x => x.Options.OptionType == 1
&& x.Options.QualifierId != null
&& x.Options.CreditingMethod != "xxx")
.Select(y => new DataModel.Table1()
{
Years = y.Select(a => a.OptionsCosts.Years).FirstOrDefault(),
Strike = y.Select(a => a.OptionsCosts.Strike).FirstOrDefault(),
Value = y.Select(a => a.OptionsCosts.Value).FirstOrDefault(),
ChangeUser = y.Select(a => a.OptionsCosts.ChangeUser).FirstOrDefault(),
ChangeDate = DateTime.Now,
OptionId = y.Select(a => a.OptionsCosts.OptionId).FirstOrDefault()
});
Here is the SQL that I'm trying to convert:
SELECT o2.OptionId, o2.Years, o2.Strike, SUM(d2.Weights) as 'TotalWeight', COUNT(*) as 'Counts'
FROM Table1 o2
INNER JOIN #Dates d2 --this is a temp table that just holds dates. I was thinking just a where statement could do it???
ON d2.EffectiveDate = o2.EffectiveDate
INNER JOIN Table2 od2
ON od2.OptionId = o2.OptionId
AND od2.OptionType = 1
AND od2.qualifierid is null
AND od2.CreditingMethod <> 'xxx' --28095
GROUP BY o2.OptionId,o2.Years, o2.Strike
My data is way off so I'm sure I'm doing something wrong.

var table1=_context.Table1
.groupBy(o2=> new{
o2.OptionId
, o2.Years
, o2.Strike
})
.select(s=> new{
s.key.OptionId
, s.key.Years
, s.key.Strike
,TotalWeight=s.sum(x=>x.Weights)
,Counts=o2.count(c=>c.OptionId)
}).tolist();
var result=table1
.Join(_context.Table2,oc => oc.OptionId, o => o.OptionId, (oc, o) => new{ OptionsCosts = oc, Options = o })
.Where(x => x.Options.OptionType == 1
&& x.Options.QualifierId != null
&& x.Options.CreditingMethod != "xxx")
.select(x=> new {
x.oc.OptionId, x.oc.Years, x.oc.Strike, x.oc.TotalWeight, x.oc.Counts
}).tolist();

Small advise, when you rewriting SQL queries, use LINQ Query syntax which is close to SQL and more effective to avoid errors.
var dates = new List<DateTime>() { DateTime.Now }; // fill list
var query =
from o2 in _context.Table1
where dates.Contains(o2.EffectiveDate)
from od2 in _context.Table1.Where(od2 => // another way to join
od2.OptionId == o2.OptionId
&& od2.OptionType == 1
&& od2.qualifierid == null
&& od2.CreditingMethod != "xxx")
group o2 by new { o2.OptionId, o2.Years, o2.Strike } into g
select new
{
g.Key.OptionId,
g.Key.Years,
g.Key.Strike,
Counts = g.Count()
// SUM(d2.Weights) as 'TotalWeight', -this one is not available because dates in memory
};
If you are on start and trying to rewrite procedures on LINQ - EF Core is bad idea. Too limited IQueryable support and usually you will fight for each complex LINQ query.
Try linq2db which has temporary tables support and your stored proc can be rewritten into identical LINQ queries. Or you can use linq2db.EntityFrameworkCore to extend EF Core functionality.
Disclaimer. I’m creator of this extension and one from linq2db creators.

How to do this query using expression in LINQ?

select t.*
from Task t
inner join Project p on a.ProjectId = t.ProjectId
where p.ProjectTypeId IN ( select ptg.ProjectTypeId
from UserGroup ug
inner join ProjectTypeGroup ptg on ug.GroupId = ptg.GroupId
where ug.UserId = 1 -- MUTABLE VALUE
)

In the attempt query given by you, I don't see Task being used.
Since there is no relation between your sub-query and your main query, you should split them in to two queries:
var projTypeIds = (from ug in UserGroup
join ptg in ProjectTypGroup on ug.GroupId equals ptg.GroupId
where ug.UserId == 1
select ptg.ProjectTypeId).ToList()
Once you have your output, check for .Contains
var task = (from t in Task
join p in Project on p.ProjectId equals t.ProjectId
where projTypeIds.Contains(p.ProjectTypeId)
select t).FirstOrDefault();
I assume you need only one object from this query hence used .FirstOrDefault(), if you are expecting a list using .ToList()

You can use this.
from t in Task
join p in Project
on t.ProjectId equals p.ProjectId
let subQ = ( from ug in UserGroup
join ptg in ProjectTypeGroup
on ug.GroupId equals ptg.GroupId
where ug.UserId == 1
select ptg.ProjectTypeId)
where subQ.Contains(p.ProjectTypeId)
select t
or you can use this.
int loggedUserId = 1;
var _userGroups =
UserGroup.Join(ProjectTypeGroup,
t => t.GroupId, p => p.GroupId,
(t, p) => new {t, p})
.Where(n => n.t.UserId == loggedUserId)
.Select(s => s.p.ProjectTypeId);
var projectTypeIds =
Task.Join(Project,
t => t.ProjectId, p => p.ProjectId,
(t, p) => new {t, p})
.Where(n => _userGroups.Contains(n.p.ProjectTypeId) )
.Select(n => n.t);
projectTypeIds.ToList();

How can I write a linq query for this?

I need to write following query in Linq to SQL but not sure what is the best way of doing, given it has two derived tables. Any suggestions.
SELECT A.ID
FROM
(
SELECT *
FROM Orders
WHERE ProductID = 5
) A
JOIN
(
SELECT CustomerID, MAX(Price) Price
FROM Orders
WHERE ProductID = 5
GROUP BY CustomerID
) B
ON A.CustomerID = B.CustomerID and A.Price = B.Price

var b = (
from o in db.Orders
where o.ProductID == 5
group o by o.CustomerID into og
select new {
CustomerID = og.Key
Price = Max(og.Price)
}
);
var a = (
from o in db.Orders
join p in b on new {a.CustomerID, a.Price} equals
new {b.CustomerID, b.Price}
where o.ProductID == 5
select a.ID
);
var r = a.ToString();
These two links are invaluable when forming things like this:
http://code.msdn.microsoft.com/101-LINQ-Samples-3fb9811b
http://msdn.microsoft.com/en-us/vstudio/bb688085

Can you simplify this with LINQ, especially if you use method syntax instead of query syntax.
orders.Where(o => o.ProductID == 5)
.GroupBy(o => o.CustomerID)
.SelectMany(g => g.Where(o => o.Price == g.Max(m => m.Price)));
My advice when writing LINQ, do not simply attempt to convert a SQL statement exactly. Think about the desired result and develop a solution designed for LINQ.

Something along these lines:
var result = from a in context.Orders
join b in (context.Orders.Where(o => o.ProductID == 5).GroupBy(o => o.CustomerID).Select(g => new { CustomerID = g.Key, Price = g.Max(o => o.Price)))
on new {a.CustomerID, a.Price} equals new {b.CustomerID, b.Price}
where a.ProductID == 5
select a.ID;

Efficient way to sub Queries in Linq

here is my linq code:
BOOK entity = db.BOOKS
.Where(s => s.ID == (from p in db.LIBRARY
from b in db.BOOKS
where (p.ID == 123) && (p.idpage == b.idpage)
select b.fields));
My actual oracle code is:
SELECT DISTINCT BOOKS.ID
FROM LIBRARY,BOOKS
WHERE LIBRARY.ID = 123 AND LIBRARY.ID = BOOKS.ID
But its showing the error in s.ID that..
Delegate 'System.Func Project.Models.BOOKS,int,bool' does not take 1 arguments
Why does this happen? Are there any workarounds?

Your SQL is using a join, so you can do the same thing in LINQ. Either of these approaches will suffice:
// join
var query = (from b in db.BOOKS
join p in db.LIBRARY on b.IdPage equals p.IdPage
where p.ID == 123
select b.Id).Distinct();
// 2 from statements (SelectMany) can also be used as a join
var query = (from b in db.BOOKS
from p in db.LIBRARY
where p.ID == 123 && b.IdPage == p.IdPage
select b.Id).Distinct();
// fluent syntax
var query = db.BOOKS
.Where(b => db.LIBRARY.Any(p =>
p.ID == 123 && b.IdPage == p.IdPage))
.Select(b => b.Id)
.Distinct();

s.ID is comparing to an Enumerable, so you get the error.
At the end of the LINQ query, add a SingleOrDefault().

Your subquery returns a sequence of values, not a single values, so you can't compare it to a scalar property like ID. You should use First on the result of the subquery to get the first result (or Single if there should be only one)
BOOK entity = db.BOOKS
.Where(s => s.ID == (from p in db.LIBRARY
from b in db.BOOKS
where (p.ID == 123) && (p.idpage == b.idpage)
select b.fields).First());

You should be able to use the navigation properties on your BOOKS class to do something like this:
var bookIds = db.BOOKS.Where(b => b.LIBRARIES.Any(l => l.ID == 123))
.Select(b => b.ID)