[dna-dev] Recent changes to the connector framework

[Randall Hauch]

I just finished working on some big changes to the connector  
framework.  All the detail regarding the issue and the design can be  
found in DNA-281 (https://jira.jboss.org/jira/browse/DNA-281).   
However, this is a fairly significant change, so I wanted to let  
everyone know what's going on.  (The commit email was actually too  
big, which is another reason for this email).

The problem stems from not having a perfect mapping between a  
connector and the notion of a JCR workspace.  When we came up with the  
initial connector design, we'd hoped that a connector would map to a  
JCR workspace, and that we could just create multiple sources  
(instances of connectors) when we need multiple workspaces.   
Unfortunately, some of the workspace-level operations in JCR don't  
work too well with this.  In particular, creating workspaces would  
have entailed setting up new RepositorySource instances, which is  
difficult if you have to also set up the back end system, like a  
database.  To really fix this, we need a connector to be able to have  
multiple workspaces and to support creating, cloning, and destroying  
workspaces.

Normally, this would be that much of a surprise.  We've always  
followed the evolutionary approach to design and development.  So this  
change wouldn't really be that special - if it weren't for the size of  
the change.  The connector API is affected, which means that each  
connector implementation is affected.  Also, the Graph API is affected  
because we need to expose these new operations.  And this meant that  
every code that used the Graph API may be affected, since they now  
need to possibly have some notion of a workspace.  All in all, a lot  
of code has been impacted by this.  And I spent several days trying  
different approaches that were incremental, and nothing worked.  I had  
no choice but to make all the changes at once.

Interestingly, while making the changes, I discovered a bug in the  
federation code (DNA-282), and a number of existing test cases fail.   
And of course the Getting Started repository example fails because it  
relies up the federation connector.  So, rather than complicate an  
already mess of a commit set, I decided to temporarily remove these  
two projects from the build.

Similarly, I have local changes to the JCR project to support writing  
(which was the ultimate reason why support for workspaces was needed  
in the first place).  And these changes aren't quite complete enough  
to commit, yet I didn't want to spent a lot of time fixing test cases  
that I'll be making changes to.  So this project was also pulled from  
the build, too.

My apologies for the state of the project, and for this massive  
commit.  I dislike these large changes with a passion, but just  
couldn't figure out a way to get around it.  But everything compiles,  
and all tests (except those listed above) run successfully.

For those of you working on connector implementations, feel free to  
look at the in-memory connector, the JBoss Cache connector, or the JPA  
Store connector.   Specifically, look in the RequestProcessor  
implementation classes in the connectors, since that's where all the  
interesting stuff is.  Of course, some of the source implementations  
have properties that define the names of "predefined workspaces" and a  
"default workspace", and that may be of use to you.  These all support  
multiple workspaces, but in slightly different ways.  I think the  
notion of workspaces would work really well in a couple of our  
connectors, including SVN and JDBC metadata.  Of course, if you have  
any questions, please post to this list.

Best regards,

Randall
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