[rules-users] Null pointers and field level validation

[Ronald Albury]

I have been experimenting with using the same set of rules for both record
validation (when a completed record come to us from a 3rd party) and field
validation (when the record is filled out via a web app).  I don't want to
have two separate sets of rule validation (twice the maintenance, twice the
confusion).  I have no problems with the record validation, but some issues
with field validation that I would like to get input on.

First - the idea for the field validation is to use Ajax to send the field
contents to the server when the field looses focus, so that we can provide
rapid feedback to the user if they have entered a field incorrectly.  Most
of the intra-field validation will take place at the end of the user input,
when the form is submitted.

The fact that Drools has lots of null protection was very helpful ... I
could partially fill in a sub-record with the field input, submit it to the
rules engine, and only those rules accessing a filled-in (non-null) field
would be evaluated.  I am interested in feedback on this concept.

The general issue I'm having with my experiment is that not all
null-security is created equal.
   1) if I have a Boolean field then Drools throws an exception if the rule
is based on that field and the field is null.  I found a work around by
testing if the field is equal to true.
   2) if I have a String field then Drools throws an exception if that
field is tested with 'matches'.  The only work around I've come up with is
to use a null-protected utility method instead of the built-in 'matches'.
   3) if I have a String field then Drools throws an exception if that
field is tested with 'in'. Here again, the only work around I've come up
with is a utility method.

Is my concept flawed from the start? Any suggestions on addressing the
issues mentioned above?  Any suggestions on issues I have yet to encounter?

Thanks
   Ron
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