EF Core does not lock table from read

Question

I need to do status check before insert data, but I found EF Core does not lock table from read even I setup isolationlevel.

Here is my code: I need to lock SignTicket table and SignTicketApproval table from read until commit, so that others will not get false data about ticket status. But even I setup the isolation level, I can still read table in SSMS.

I need a table-level lock, because this is a insert-only table, every operation must check the latest record to determine the status of ticket.

Thank you.

using var _context = new EFContext();

using var transaction = _context.Database.BeginTransaction(System.Data.IsolationLevel.Serializable);

var ticket = _context.SignTicket
                     .Include(x => x.SignTicketApproval)
                     .ThenInclude(x => x.Result)
                     .Single(x => x.Id == cancelSignTicketRequest.SignTicketId.ToLong());

if (_signTicketService.GetTicketStatus(ticket) != TicketStatus.Open)
{
    throw new SignTicketStatusException("Ticket status is not open", ticket);
}

// Create new fake approval request and set __Cancel as outcome
var utcNow = DateTime.UtcNow;

var cancelSignoff = new SignTicketApproval()
            {
                AssignedTo = cancelSignTicketRequest.CanceledBy,
                Description = "User cancel",
                CreateTime = utcNow,
                Result = new SignTicketApprovalResult()
                {
                    Canceled = true,
                    ApproverEmail = cancelSignTicketRequest.CanceledBy,
                    CreateTime = utcNow,
                    Outcome = ReservedButton.CancelButton,
                    Comment = cancelSignTicketRequest.Reason
                }
            };

ticket.SignTicketApproval.Add(cancelSignoff);

_context.SaveChanges();
transaction.Commit();