Jena Event Handling

[graham <gr...@orangedogsoftware.com>]

Hi

The documentation for Jena event handling says the following: "In the 
current design, listeners are not informed of transaction boundaries, 
and all events are fed to listeners as soon as they happen".

This leads me to a question. I have a piece of code as follows:

     database.begin(ReadWrite.WRITE);
     model = storage.database.getDefaultModel();

     add statement 1 to the model

     add statement 2 to the model
     ...

     add statement N to the model

     database.commit();
     storage.database.end();

I have another piece of code listening for changes in the database model.

How can that listening piece of code reliably detect that *all* 
statements 1 through N have been added to the model, and hence the model 
can be queried for whatever was added?

thanks

graham

Re: Jena Event Handling

[Andy Seaborne <an...@apache.org>]

graham,

Events and transaction isolation doesn't mix.  Why being added, any 
triples aren't visible outside the transaction; transactions can abort 
resulting in no changes.  So a kind of "within transaction" event might 
make some sense (abort aside) but as a general concept it's a bit messy.

The best way to know 1-N have been added is to listen for the commit. 
Use a DatasetGraphWrapper with the underlying DatasetGraph (or write a 
DatasetWrapper - Dataset must be the only abstraction in ARQ without a 
paired wrapper!).

Now you can add code before/after a commit to know when that point has 
been reached.

     Andy

https://afs.github.io/rdf-delta/ is a system for capturing changes.  It 
has a DatasetGraphChanges wheer you can add a listener and get all 
adds/deletes and transaction boundaries. It is not part of Apache Jena. 
It does work with it.

On 06/08/18 04:49, graham wrote:
> Hi
> 
> The documentation for Jena event handling says the following: "In the 
> current design, listeners are not informed of transaction boundaries, 
> and all events are fed to listeners as soon as they happen".
> 
> This leads me to a question. I have a piece of code as follows:
> 
>      database.begin(ReadWrite.WRITE);
>      model = storage.database.getDefaultModel();
> 
>      add statement 1 to the model
> 
>      add statement 2 to the model
>      ...
> 
>      add statement N to the model
> 
>      database.commit();
>      storage.database.end();
> 
> I have another piece of code listening for changes in the database model.
> 
> How can that listening piece of code reliably detect that *all* 
> statements 1 through N have been added to the model, and hence the model 
> can be queried for whatever was added?
> 
> thanks
> 
> graham
> 
>