[rules-users] Type Declaration upgrade

[Mark Proctor]

On 14/02/2011 18:10, Edson Tirelli wrote:
>
>    The current version of Drools does not support dynamic changes in 
> "type declarations" and I don't see this changing anytime soon. The 
> reason is that not only the actual fact would require changes, but the 
> actual knowledge base would require changes as several nodes might be 
> referencing the old class.
>
>    So, to update a fact type you need to recreate the knowledge base. 
> This is the same, BTW, than changing one of your fact classes in your 
> application jars... you need to recompile the knowledge base or you 
> will end up with class cast exceptions, sooner or later.
Longer term there are two ways to achieve this
1) type declarations can only be modified if there is no data on them 
and the existing rules are still valid after the change, i.e. it will 
not effect the current state.

2) If ther eare existing facts a migration script must be provided that 
handles the mapping as all beans would need to be copied to the new type 
declaration.

Mark
>
>     Edson
>
> 2011/2/14 delete <boyun.yuriy at gmail.com <mailto:boyun.yuriy at gmail.com>>
>
>
>     Hi.
>     I have such declaration of type
>     declare Contact
>      firstName : String
>     end
>
>     then I want to add new property to this type. so the  next version is
>     declare Contact
>      firstName : String
>      newField : String
>     end
>
>     this type declaration is in separate drl file.
>     then I add this new type to current KnowledgeBase.
>     but when I execute knowledgeBase.getFactType("test.package",
>     "Contact");
>     I get old version of Contact.
>
>     During debugging I found the place where is should be upgraded in the
>     KnowledgeBase.
>     org.drools.common.AbstractRuleBase.mergePackage
>     there is
>     // merge the type declarations
>            if ( newPkg.getTypeDeclarations() != null ) {
>                // add type declarations
>                for ( TypeDeclaration type :
>     newPkg.getTypeDeclarations().values() ) {
>                    // @TODO should we allow overrides? only if the
>     class is not
>     in use.
>                    if ( !pkg.getTypeDeclarations().containsKey(
>     type.getTypeName() ) ) {
>                        // add to package list of type declarations
>                        pkg.addTypeDeclaration( type );
>                    }
>                }
>            }
>
>     so according this comments it's not possible to upgrade Type on
>     the fly.
>
>     Am I missing something?
>     Does someone had such problems or know the workaround.
>
>     Thanks in advance,
>     Yuriy
>
>     --
>     View this message in context:
>     http://drools-java-rules-engine.46999.n3.nabble.com/Type-Declaration-upgrade-tp2491975p2491975.html
>     Sent from the Drools - User mailing list archive at Nabble.com.
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>
>
>
>
> -- 
>   Edson Tirelli
>   JBoss Drools Core Development
>   JBoss by Red Hat @ www.jboss.com <http://www.jboss.com>
>
>
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