[jbosscache-dev] VAM integration in JDBCCL - updating an empty node from database results on a put() on Collections.emptyMap()

[Manik Surtani]

On 14 Dec 2006, at 20:42, Galder Zamarreno wrote:

> Hi,
>
> I'm in the process of integrating VersionAwareMarshaller with  
> JBDCCacheLoader and I've found an issue in TreeCacheMarshaller200.  
> unmarshallMap().
>
> Let's say I make a put (single key/value pair) in the cache which  
> results in an insert of a marshalled map in the db. I then call  
> remove(key) which results on the map still being in the db but  
> containing no data.
>
> If I evict the data from memory and call put() again, unmarshallMap 
> () would return Collections.emptyMap() which returns an immutable  
> empty map. When I try putting my new data into the map, it throws  
> java.lang.UnsupportedOperationException which is expected as the  
> map is immutable.
>
> I had a quick chat with Brian and the first solution was to check  
> for isEmpty() but as Brian pointed out,
>
> "If VAM is meant to be a general purpose tool, it needs to work in  
> a general purpose way, if code that uses it needs to understand  
> it's internal details and code around them, that's improper"
>
> He also said: "well VAM is just assuming that the only purpose of  
> the map is to be an argument in a put call.  if VAM is to be  
> general purpose it can't make such assumptions, or needs to expose  
> an API to turn them on/off per request"
>
> I think Brian is right. Currently, JDBCCL checks values from  
> JDBCCL.loadNode() based on the contract of this method, and  
> therefore, should not really now what could come from VAM.
>
> Thoughts?

I'd treat TCM200.unmarshallMap() returning Collections.emptyMap() as  
a bug!  It should return a *usable* map even if it is empty.  I  
probably used this as a short-sighted optimisation.

	if (mapSize == 0) return new HashMap(); //much better/more  
generically usable!



>
> Galder Zamarreño
> Sr. Software Maintenance Engineer
> JBoss, a division of Red Hat
>
> IT executives: Red Hat still #1 for value http://www.redhat.com/ 
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>
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