[rules-dev] need advice re null handling

[Michael Neale]

Felipe - yes that is consistent.

But what about:

Fact( field != 3 )
now if field is null, its certainly not equal to 3, but should this be true?
or because of null, it is always false?

In SQL, it would always be false.

On 3/16/07, Felipe Piccolini <felipe.piccolini at bluesoft.cl> wrote:
>
> I think Im not agree with that... the question here is about how the Rule
> languaje will treat an expresionmade by a businness agent to the rules...
> so when a rule has a condition writen like this:
>      Fact( field > 3)
>   this is asking : Is there a fact of type Fact which has a field and the
> value of that value is greater that 3..
>
> So, if the Fact actually exists and for 'some reason' its field "field"
> has a value which is not greater than 3
> (the rule doesn't need to know why the value is not 3, or is 0, or null or
> whatever) then the condition must
> return (or been evaluated as) false. Its responsability for the DAO or
> fill implementation of the fact to put the
> right value on its fields, the values that MEAN something. If its null it
> is possible that the value was never
> setted or initialized, or maybe it means something else. If a bussiness
> guy wants to ask for been null
>    Fact( field == null)
> then that question is a meaningfull one, dont let programmers decide what
> it means. If I wanna to ask for
> being greater that 3, and it has no value, then the answer is NO, "it is
> NO greather than 3".
>
> well... this is just my humile opinion btw....
>
>
>
> On 15-03-2007, at 13:03, Tom Gonzalez wrote:
>
> We handle it as it can't be anything else but null cause null is returned
> when an access fails or some error occurs. This keeps it from falling into a
> valid evaluation and possibly a subtle bug going uncaught.
>
> Tom G
>
>  ------------------------------
> *From:* rules-dev-bounces at lists.jboss.org [
> mailto:rules-dev-bounces at lists.jboss.org<rules-dev-bounces at lists.jboss.org>]
> *On Behalf Of *Mark Proctor
> *Sent:* Thursday, March 15, 2007 12:42 PM
> *To:* Rules Dev List
> *Subject:* Re: [rules-dev] need advice re null handling
>
> Its not about giving it up, its how we handle when those fields are null,
> do we treat it like a primitive and assume its 0, or do we say it can't be
> equal to anything else but null.
>
> In the following example neither y or z is defined, thus y is null and z
> is 0;
>
> int x = 0;
> Integer y;
> in z;
> x == y // is false;
> x == z // is true
> y == null // is true
>
> Mark
>
> Tom Gonzalez wrote:
>
> The flexibility provided by an Object is very valuable. We use Integer and
> String objects all over the place today in our facts with drools. I would
> hate to give it up.
>
> Tom G
>
>  ------------------------------
> *From:* rules-dev-bounces at lists.jboss.org [
> mailto:rules-dev-bounces at lists.jboss.org<rules-dev-bounces at lists.jboss.org>]
> *On Behalf Of *Mark Proctor
> *Sent:* Thursday, March 15, 2007 6:29 AM
> *To:* Rules Dev List
> *Subject:* Re: [rules-dev] need advice re null handling
>
> if bar is an integer it will be 0, if its an Integer it will be null. The
> Q is do we make Integer work like the primitive, or do we make it work like
> an Object.
>
> Mark
> Michael Neale wrote:
>
> http://jira.jboss.com/jira/browse/JBRULES-627
>
> OK, this much is clear:
>
> Foo(field == null) can be true if field is null.
>
> but, what about Foo(field > 3), and field is null? should that be false?
> what about Foo(field != 3) - should that be true?
>
> in SQL, null will always result in a false condition, unless you
> explicitly use null.
>
> Thoughts?
>
> Michael.
>
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>
>                                                                         *Felipe
> Piccolini M.*
> felipe.piccolini at bluesoft.cl
>
>
>
>
>
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