[rules-users] qualified identifiers in constraints: not commutative?

[Michael Whidden]

Thanks again, but your read of the "small print" perhaps explains why
the parens make (o.q > (o.b.maxQ)) work, but does not explain why
(o.q > o.b.maxQ) does not work while (o.b.maxQ < o.q) does work.


On 12/31/2010 3:18 PM, Wolfgang Laun wrote:
> On 31 December 2010 19:05, Michael Whidden <mwhidden at thebluew.com
> <mailto:mwhidden at thebluew.com>> wrote:
>
>     Thank you! That fixes it, without using getter methods. So did I make a
>     mistake, or is this a workaround for a bug?
>
>
> Very careful reading of the very, very small print in the Expert manual
> section describing the various forms of field constraints will tell you
> that one of the forms of single value restrictions is the "Return Value
> Restriction", a parhenthesized expressiion, which is the form where any
> Java expression is permitted. (The alternatives use either a literal, a
> variable or a qualified identifier. Your construct would qualify
> syntactically for the latter - I'm not sure where the current Drools
> version draws the line; future releases might relax this limitation.)
>
> Seemingly unnecessary parentheses are the distinction for the Drools
> parser to throw the contents into the generated Java code "as is".
>
> -W
>
>
>     These work:
>     $o:Order(q > (b.maxQ))
>     $o:Order($o.q > ($o.b.maxQ))
>     $o:Order(b.maxQ > q)
>     $o:Order($o.b.maxQ > $o.q)
>
>     These don't:
>     $o:Order(q > b.maxQ)
>     $o:Order($o.q > $o.b.maxQ)
>
>     Is this proper behavior, or a bug? I can't find anything in the docs
>     that describes the parens as required when a qualified identifier
>     appears on the right side of a binary operator in a constraint.
>
>
>     On 12/31/2010 11:47 AM, Wolfgang Laun wrote:
>      > Try parenthesizing the right hand side but note that you may have
>     to use
>      > getters to access the fields
>      >     $o:Order($o.q > ($o.getB().getMaxQ() ) )
>      >
>      > It's possible that using dialect "mvel" might be a way to avoid using
>      > the getX() instead of x.
>      >
>      > -W
>      >
>      >
>      > On 31 December 2010 17:30, Michael Whidden <mwhidden at thebluew.com
>     <mailto:mwhidden at thebluew.com>
>      > <mailto:mwhidden at thebluew.com <mailto:mwhidden at thebluew.com>>> wrote:
>      >
>      >     At Mr. Legendre's suggestion, I removed the $o from my
>     constraints, but
>      >     with the same result: (b.maxQ < q) works, but (q > b.maxQ)
>     fails. I get
>      >     the error:
>      > "Unable to create restriction '[QualifiedIndentifierRestr: <
>     b.maxQ ]'
>      >     for field 'quantity' in the rule 'MaxQty'"
>      >
>      >
>      >
>      >     On 12/30/2010 2:32 PM, Michael Whidden wrote:
>      > > I notice an unexpected behavior when creating a technical DRL in
>      >     Guvnor.
>      > >
>      > > If I have a fact with a sub-fact, then binary operators don't
>      >     seem to be
>      > > commutative.
>      > >
>      > > Eg.,
>      > >
>      > > declare Broker
>      > > maxQ: Integer
>      > >
>      > > declare Order
>      > > q: Integer
>      > > b: Broker
>      > >
>      > > The rule
>      > > $o:Order($o.b.maxQ < $o.q)
>      > > validates fine, but
>      > > $o:Order($o.q > $o.b.maxQ)
>      > > returns an error "Unable to create restriction
>      > > '[QualifiedIndentifierRestr: > $o.broker.maxQ ]' for field '$o.q'
>      >     in the
>      > > rule"
>      > >
>      > > I'm new, so I want to make sure I'm not missing something obvious
>      >     here...
>      >
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