Expression type 'NhSumExpression' is not supported by this SelectClauseVisitor

问题

I have a query that I can run in LinqPad, but not in NHibernate LINQ. I found a similar bug on NHibernate Jira NHibernate NH-2865, but I think this perhaps a different bug and I'm looking for possible alternatives.

The query that works in LinqPad using default LINQ to SQL is like this:

from ticket in LotteryTickets
  group tiket by ticket.ticketType into g

 select new
 {
     TicketType = g.Key,
     TotalWinningTickets = g.Count(b => b.WinAmount != 0),
     TotalWon = g.Sum(b => b.WinAmount * b.ticketWeight),
     TotalTickets = g.Count(),
 }

There are various other ways to count the TotalWinningTickets such as TotalWinningTickets = g.Sum(t => t.WinAmount > 0 ? 1 : 0) or g.Sum(t => t.WinAmount == 0 ? 0 : 1)

Now, with NHibernate LINQ I have been unable to get this working without changing my underlying db table. My alternative was to add a table column called HasWon and I set it to 0 for false and 1 for true. This does work, but I'm left feeling there is a better way other than modifying the db table. Perhaps a subselect using a calculated field. My NHibernate LINQ ended up looking like this:

from ticket in session.Query<Ticket>()
group ticket by ticket.TicketType into g
select new ReportRow
{
    TicketType = g.Key,
    TotalWinningBets = g.Sum(t => t.HasWon),
    TotalTickets = g.Count(),
    TotalWon = g.Sum(t => t.WinAmount * t.WagerWeight)
};

What I'm effectively trying to do is multiple Select COUNT in my NHibernate query, but based on different criteria. The strangest this is that NHibernate converts all my Count(t => t.???) incorrectly into COUNT(*) in the generated SQL.

LinqPad generates SQL that works this way: SELECT SUM( (CASE WHEN [t1].[WinAmount] > @p3 THEN @p4 ELSE @p5 END)) AS [value]

Hoping there is a better way.

来源：https://stackoverflow.com/questions/15015662/expression-type-nhsumexpression-is-not-supported-by-this-selectclausevisitor

标签

nhibernate

linq-to-nhibernate