[rules-users] null POJO attribute causing template issues -- is there a better way?

[Wolfgang Laun]

In my opinion, the best technique is to implement the fact classes in
a way that avoids null as a return value for any attribute. In your
case, the caveat might be set to the empty string ("") and that would
solve your problem nicely.

-W



On 30/01/2012, dunnlow <dunnlow at yahoo.com> wrote:
> Hi,
> I'm using a template to validate information in my POJO.  I've got a row for
> the different valid possibilities.
>
> My template rule (in guvnor) looks like:
>
> WHEN
> There is a MyBean[$mb] with:
>     itemname matches templateItemName
>     cost greater than templateCost
>     caveat matches templateCaveat
> THEN
> . 8<
>
> (I have columns in my template for templateItemName, templateCost and
> templateCaveat).
>
> Almost always, I don't care about the value in $mb.caveat, so I have a ".*"
> in the entry for that row.  This works fine as long as $mb bean has a caveat
> (ie, $mb.caveat !=null).  But when caveat is null the check for caveat
> matches templateCaveat (where templateCaveat = ".*") fails.  I tried the
> regex ".*|null" but that doesn't work either, which I suppose isn't so
> surprising (although I never see a NPE error msg).
>
> Modifying the template like this doesn't work:
>
>     itemname matches templateItemName
>     cost greater than templateCost
>     any of the following:
>           caveat==null
>           caveat matches templateCaveat
>
> because when a null valued caveat comes in, this then matches both the rule
> I want to fire and the lone one or two with a constraint on that field
> (something other than ".*").  I know I can set the salience so that the rows
> with ".*" fire first, but that seems REALLY ugly.
>
> I also considered putting in a rule with a high salience that adds a dummy
> caveat if one doesn't exist, but this still seems somewhat ugly.
>
> What I'd like to do is have a constraint such as: if caveat matches
> templateCaveat or (if caveat is null and templateCaveat does not match ".*")
>
> Does anyone have any insight about the best way to implement this?
>
> Thank you,
> -J
>
>
>
>
>
> --
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> http://drools.46999.n3.nabble.com/null-POJO-attribute-causing-template-issues-is-there-a-better-way-tp3701360p3701360.html
> Sent from the Drools: User forum mailing list archive at Nabble.com.
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