[rules-users] Identity, equality, hashing and indexing

[Bruno Freudensprung]

Hi Thomas,

Thanks for your answer! You actually describe the behavior what I was 
hoping for :-).

Bruno.

Swindells, Thomas a écrit :
> Drools only cares about facts, not the fields within it - when you tell Drools you have updated a fact object then it re-evaluates all the rules that uses the fact, you don't tell it which fields have actually changed. Therefore you can have inter-related fields without any problems.
>
> I don't know for sure but I think that when you use update to tell drools the object has been updated it will update the hashcode to the new value and so maintain the checking of equality.
>
> Thomas
>
>   
>> -----Original Message-----
>> From: rules-users-bounces at lists.jboss.org [mailto:rules-users-
>> bounces at lists.jboss.org] On Behalf Of Bruno Freudensprung
>> Sent: 08 December 2010 14:00
>> To: Rules Users List
>> Subject: [rules-users] Identity, equality, hashing and indexing
>>
>> Hi,
>>
>> I have some existential questions about Drools Expert's magic :-).
>>
>> When reading the documentation it is clear that, by default, facts are
>> stored in an IdentityHashMap. If I understand things correctly it means
>> that the objects I put in the working memory don't have to implement the
>> hashCode() and equals() method. They should implement them only if I
>> tell Drools to use the "equality mode".
>>
>> So here is my first question: in equality mode, if a fact field is used
>> by the hashCode method, and if that field is modified by a rule action,
>> should I expect a weird behavior since facts are stored in a HashMap?
>>
>> When digging into rules-users' archives I also found posts of Mark
>> Proctor, talking about field indexing and alpha node hashing, that lead
>> to my second question: should I expect a weird behavior if 2 fields are
>> related to each other?
>> For instance (not a good example but it gives an idea): a Person type
>> has a getFirstName() method, a getLastName() method and a getName()
>> method that return the concatenation of getFirstName() and getLastName().
>> Is it problematic if one rule has a "Person(name == "John Doe")" fact in
>> its LHS and if another rule modifies the "firstName" of that Person fact
>> (John -> Jane)?
>> Does it depend on the equality vs. identity mode (I don't think so...
>> unless the field itself is a also a fact)?
>>
>> Many thanks in advance for your answers,
>> Best regards,
>>
>> Bruno.
>>
>>
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>> https://lists.jboss.org/mailman/listinfo/rules-users
>>     
>
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