LINQ to SQL compare nullable in subquery - entity-framework

Question

I fail to translate a sql query to a linq query that could calculate some stock.
This is my test query that I'm trying to convert to a linq query.
SELECT
i.*,
(SELECT COUNT(t.*) FROM tickets t
WHERE t.starttime::time = i.sessionstarttime::time
AND t.starttime::date = '2018-04-06'::date)
as stock
FROM items I
-- note that the hardcoded date ('2018-04-06') is a function parameter
( tl;dr; how would you convert this PostgreSQL query to LINQ? )
My attempts so far are the variations of the following query:
var items = await _context.Items.Select(x => new Item
{
Id = x.Id,
IsTicket = x.IsTicket,
Name = x.Name,
Price = x.Price,
SaleItems = x.SaleItems,
SessionStartTime = x.SessionStartTime,
DateCreated = x.DateCreated,
DateEdit = x.DateEdit,
UserIdCreated = x.UserIdCreated,
UserIdEdited = x.UserIdEdited,
// calculate stock in subquery
Stock = _context.Tickets.Count(
t => t.StartTime.Date == ticketDate
&& x.SessionStartTime.HasValue
&& t.StartTime.Hour == x.SessionStartTime.Value.Hours // this is the part that is failing
&& t.State != TicketState.Canceled)
}).ToListAsync();
t.StartTime is Datetime and x.SessionStartTime is Nullable Timespan
So when I comment the line && t.StartTime.Hour == x.SessionStartTime.Value.Hours everything is fine, but with it I get warnings that it could not be translated and will be evaluated locally. But I don't want to download the whole ticket table just to count them.
The t.StartTime.Hour part is fine, I tried to perform static comparisons with both parameters. t.StartTime.Hour == 5 was translated without any problems, but x.SessionStartTime.Value.Hours == 5 failed to translate.
Also the problematic part in the application output:
([t].StartTime.Hour == Convert([x].SessionStartTime, TimeSpan).Hours))
So I guess that convert part is failing.
So what I'm missing and how I could work around this problem. Any help will be appreciated.
Update:
After experimenting a bit I have found two workarounds, that I wouldn't call the answers.
First I noticed that EF is trying to convert Nullable<TimeSpan> to a regular TimeSpan from the mentioned output: ([t].StartTime.Hour == Convert([x].SessionStartTime, TimeSpan).Hours))
I thought I could prevent that conversion by converting to a string and comparing the strings (I have a feeling this will bite me in the future):
t.StartTime.ToString().Contains(x.SessionStartTime.ToString())
The second workaround is only viable for my scenario since I know the items query is final and I can materialise it without calculated Stock, and then loop through the results and calculate it on a separate query. But this seems to add additional calls to the database and sacrifice some performance.
foreach(var x in items.Where(x=>x.SessionStartTime.HasValue))
{
// accessing the t.StartTime.TimeOfDay property seems to fail the LINQ to SQL as well
var hours = x.SessionStartTime.Value.Hours;
var minutes = x.SessionStartTime.Value.Minutes;
x.Stock = _context.Tickets.Count(t => t.StartTime.Date == ticketDate
&& t.StartTime.Hour == hours
&& t.StartTime.Minute == minutes);
}