Projections.Conditional - How to use it?

Question

Anyone knows how to use Projections.Conditional to produce something like "case ... when..."

The following code gives a wrong query:

IProjection isError = Projections.Conditional( Expression.Eq( "event.LogLevel", eLogLevel.Fatal.ToString( ) ), Projections.Constant( 1 ), Projections.Constant( 0 ) );

ICriteria criteria = Session.CreateCriteria( typeof( LogEvent ), "event" )
  .Add( Restrictions.Eq( "event.ApplID", "LogEventViewer" ) )
  .SetProjection( Projections.ProjectionList( )
    .Add( Projections.GroupProperty( "event.ApplID" ) )
    .Add( Projections.RowCount( ), "TotalCount" )
    .Add( Projections.Sum( isError ), "ErrorCount" )
  );

The produced statement is incomplete and the order of the parameters is wrong.

exec sp_executesql N'
  SELECT this_.strApplID as y0_
    , count(distinct this_.lngLogEventID) as y1_ 
    , sum((case when this_.strLogLevel = ? then ? else ? end)) as y2_
    , this_.strApplID as y3_ 
  FROM qryLogEvent this_ 
  WHERE this_.strApplID = @p0 
  GROUP BY this_.strApplID' 
,N'@p0 nvarchar(5),@p1 int,@p2 int,@p3 nvarchar(14)'
,@p0=N'Fatal',@p1=1,@p2=0,@p3=N'LogEventViewer' 

what is the correct way to use Projections.Conditional?

Answer 1

UPDATE: The issue (NH1911) is now marked as fixed in version 2.1.1.GA. Try checking that one out!

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It seems to be the use of named and positional parameters together. It does seem to be a bug, as you must have concluded too:

https://nhibernate.jira.com/browse/NH-1911

Projections.Constant uses positional and the Restriction.Eq uses named parameters. That messes up the order as desribed here, though this issue should have been fixed:

https://forum.hibernate.org/viewtopic.php?f=25&t=985944&start=0