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GroupBy in subquery with MAX() in C#

I Have this code. It works fine but when I have two same maximal values it appear 2 times. So I need to use OrderBy. But I dont know how. Thanks for any help.
IQueryable<PerformanceRealization> pr = _context.PerformanceRealization
.Where(u => u.Deadline == _context.PerformanceRealization
.Where(x => x.GroupRealizationId == u.GroupRealizationId)
.Max(x => x.Deadline)
)
.Select(u => u);
Here is the SQL code with GROUP BY
SELECT PR.GroupRealizationId
FROM Stores.PerformanceRealization PR
LEFT JOIN Stores.GroupRealization ON Stores.GroupRealization.Id = PR.GroupRealizationId
WHERE PR.Deadline = (SELECT MAX(Deadline)
FROM Stores.PerformanceRealization PR2
WHERE PR.GroupRealizationId = PR2.GroupRealizationId)
GROUP BY PR.GroupRealizationId

You can select the first object from the group
IQueryable<PerformanceRealization> pr2 = pr
.GroupBy(x => x.GroupRealizationId)
.Select(g => g.First());
If you need a specific object from the group, then you can order by another column
IQueryable<PerformanceRealization> pr2 = pr
.GroupBy(x => x.GroupRealizationId)
.Select(g => g.OrderBy(x => x.SomeColumn).First());
for SomeColumn having the smallest value. For the greatest value, use OderByDescending instead.
Of course, you can integrate this approach into the first query:
IQueryable<PerformanceRealization> pr = _context.PerformanceRealization
.Where(u => u.Deadline == _context.PerformanceRealization
.Where(x => x.GroupRealizationId == u.GroupRealizationId)
.Max(x => x.Deadline)
)
.GroupBy(x => x.GroupRealizationId)
.Select(g => g.OrderBy(x => x.SomeColumn).First());
Note, you don't need to have a Select at the end like .Select(u => u). Since it has no effect, you can just drop it.
If your EF Core version cannot handle it (as revealed in a comment), then transition to LINQ-to-Objects with AsEnumerable(), but do the filtering in EF Core to minimize the number of records sent to the front-end:
IQueryable<PerformanceRealization> pr = _context.PerformanceRealization
.Where(u => u.Deadline == _context.PerformanceRealization
.Where(x => x.GroupRealizationId == u.GroupRealizationId)
.Max(x => x.Deadline)
)
.AsEnumerable() // <===== transition from LINQ-to-EF-Core to LINQ-to-Objects
.GroupBy(x => x.GroupRealizationId)
.Select(g => g.OrderBy(x => x.SomeColumn).First());

LINQ expression to filter

I have the following LINQ expression where I am fetching Courses, Students that belong to that Course, then the School's where the Student's goes to. The following LINQ expression works fine.
However, I need to further, filter it where I need to get Students with the City == 'Colarado'. How can I alter the following LINQ to my use case.
_dbContext.Courses
.Where(c => c.Id == Id)
.Include(c => c.Students)
.ThenInclude(c => c.Schools)
.OrderByDescending(c => c.Id)
.ToListAsync();

If you need all courses and only filter students - since EF Core 5.0 you can use filtered include:
_dbContext.Courses
.Where(c => c.Id == Id)
.Include(c => c.Students.Where(s => s.City == "Colarado"))
.ThenInclude(c => c.Schools)
.OrderByDescending(c => c.Id)
.ToListAsync();

You can do the filter in the Where method.
_dbContext.Courses
.Where(c => c.Id == Id && c.Students.All(s => s.City == "Colarado"))
.Include(c => c.Students)
.ThenInclude(c => c.Schools)
.OrderByDescending(c => c.Id)
.ToListAsync();

How can i get List along with child list where child list having some condition in NHibernate

I had written a Query in NHibernate as below:
var queryResult = CurrentSession.QueryOver()
.Where(r => r.StatusId == 1)
.JoinQueryOver(a => a.ActorList)
.Where(s=>s.IsActor==1)
.List()
.Distinct()
.ToList();
I am trying to retrieve only Where(s=>s.IsActor==1), But It Is Getting Records
Where(s=>s.IsActor==0) also...
How can I get only IsActor==1 records?
Thanks in Advance

You need to specify a predicate in the join, so that it is applied to the join not the top where:
(will look something like ...LEFT JOIN actor on actor.Id = p.ActorId AND IsActor = 1)
Actor actorAlias = null;
var queryResult = CurrentSession.QueryOver()
.Where(r => r.StatusId == 1)
.Left.JoinQueryOver(r => r.ActorList, () => actorAlias, a => a.IsActor==1)
.List()
.Distinct()
.ToList();

LinQ to get the latest group of records satisfying a condition

I have below stated 2 tables:
now I want to get the set of Child Table objects for whichever their parent table entries are latest(wr.r.t lastmodified). It should be something like....
List<Child_Table> List = ChildsList.Where(x=>x.name =="pqr" && status == "done")
.Select(x=>x.Parent.lastmodified == recent record).....ToList();

You can use GroupBy on the date, then OrderByDescending on the Key then take the First followed by SelectMany to flatten the results.
var result = ChildsList.Where(x => x.name == "pqr" && x.status == "done")
.GroupBy(x => x.Parent.lastmodified)
.OrderByDescending(g => g.Key)
.First()
.SelectMany(g => g)
.ToList();

You could use a join to accomplish it:
var results = children
.Join(parents.OrderByDescending(p => p.lastmodified).Take(1),
c => c.parent_id,
p => p.id,
(c, p) => c)
.Where(x => x.name == "pqr" && x.status == "done")
.ToList();

nHibernate Subquery-WhereAll displays "not a delegate type"-error

I am trying to create a nHibernate-Query with a subquery following this blog-entry.
My working SQL looks like this:
SELECT *
FROM Product
WHERE Id IN (
SELECT p.Id
FROM Product AS p
INNER JOIN ProductSupplier AS ps
ON ps.ProductId LIKE p.Id
WHERE ps.SupplierProductNumber LIKE '102.02-7100'
GROUP BY p.Id
);
I have to group by the Id because multiple suppliers can have the same productNumber for the same product.
My nHibernate looks as following:
query.WithSubquery.WhereAll(
p => p.Id ==
QueryOver.Of<Product>()
.JoinAlias(x => x.Suppliers, () => productSupplierAlias)
.Where(() => productSupplierAlias.Product.Id == productAlias.Id)
.Where(() => productSupplierAlias.SupplierProductNumber == searchtext)
.Select(p => p.Id));
But my .Select(p => p.Id) displays
cannot convert lambda expression to type 'nHibernate.Creterian.IProjection[]' because it is not a delegate type

I don't think you should be using WhereAll in this case.
Does this work:
query.WithSubquery.WhereProperty(p => p.Id)
.In(QueryOver.Of<Product>()
.JoinAlias(x => x.Suppliers, () => productSupplierAlias)
.Where(() => productSupplierAlias.Product.Id == productAlias.Id)
.Where(() => productSupplierAlias.SupplierProductNumber == searchtext)
.Select(p => p.Id)
);