Mapstore refactoring

[sunye]

Now, MapDB and BerkeleyDB have a common code for Stores.

[gdaniel]

Can you pull the current version of master and integrate the changes I have made in DirectWrite[XX]Store? These changes are related to #54 #55, and #56 (mostly toArray and eObject methods).

[gdaniel]

@sunye nice work, I only have one concern on Store names: you simplified Store names in map-core module, which may be a good idea, but this naming convention is not followed in the sub-modules. For example DirectWriteMapDBStore extends MapStore, which may be confusing, especially because MapStore extends AbstractDirectWriteStore.

I would suggest to follow the existing convention and rename core-level stores DirectWriteMapStore, DirectWriteMapListsStore ...

@yvernageau what do you think?

Renaming all the existing DirectWrite stores (not only in Map) could be interesting, especially because all low-level stores use a direct write approach, but I think this can be done later on master.

[yvrng]

Indeed, great work!

I'm pretty agree with the naming problem, and I'm agree with its solution too.
Because the DirectWrite stores are the real implementation of a PersistentStore, and that without them, there is no link between a resource and a backend, I think that the ideal would be to simplify the DirectWrite feature at the core level. But, the confusion would then be present there, because all stores don't extends the DirectWrite feature, they simply decorate them.
So I suggest adding the notion of DirectWrite in the class names, until we find a better idea.

However, I'm agree by the simplification of the name of PersistenceBackends.

[sunye]

MapDBDirectStore and BerkeleyDBDirectStore are now empty classes and should be deleted.

I didn't keep the prefix "DirectWrite" because as long as I understand, all stores directly write things. Moreover AbstractPersistentStore is an empty class and has only 1 concrete subclass, AbstractDirectWriteStore.

I propose to remove all the "DirectWrite" prefixes and only use it if we indeed have stores with a different behavior.

[gdaniel]

@sunye There is a Read-only store in the HBase module. For now it extends DirectWriteHBaseStore, which is an issue, but I am not sure removing the prefix of other stores is interesting.

Anyway for now we need to be consistent. I propose to keep the DirectWrite prefix, merge the pull request with the updated names, and then decide what we should do about store names for all the backends (the PR here only concerns Map-based implementations).