Andy, Rob,
Thanks for the responses.
I'm using Jena 2.11.2 (same version for both TDB and ARQ).
Below are the relevant pieces of code.
Code to delete a graph:
public boolean deleteGraph(String datasetID, String graphName) {
if (!graphName.contentEquals(FusekiConfig.DEFAULT_GRAPH_NAME)) {
if (!graphExists(datasetID, graphName)) {
log.debug("[FusekiProxy] deleteGraph() - graph not found");
return false;
}
}
String directory = DBpath.concat("/" + datasetID);
Dataset dataset = TDBFactory.createDataset(directory);
dataset.begin(ReadWrite.WRITE);
try {
if (graphName.contentEquals(FusekiConfig.DEFAULT_GRAPH_NAME)) {
// special handling for default graph: we replace it with an
empty graph
dataset.getDefaultModel().removeAll();
} else {
dataset.removeNamedModel(graphName);
}
} catch(Exception ex) {
log.error("[FusekiProxy] deleteGraph() - " + ex.toString());
return false;
} finally {
dataset.commit();
dataset.end();
return true;
}
}
Code to retrieve a graph:
public String getGraph(String datasetID, String graphName, String format) {
String directory = DBpath.concat("/" + datasetID);
Dataset dataset = TDBFactory.createDataset(directory);
Model model = null;
OutputStream out = new ByteArrayOutputStream();
try {
dataset.begin(ReadWrite.READ);
if (!graphName.contentEquals(FusekiConfig.DEFAULT_GRAPH_NAME))
model = dataset.getNamedModel(graphName);
else
model = dataset.getDefaultModel();
if (model == null) {
return null;
}
// Converting retrieved graph to desired format.
/.../
} catch(Exception ex) {
log.error("[FusekiProxy getGraph() - " + ex.toString());
return null;
} finally {
dataset.end();
}
return out.toString();
}
As explained in the previous email, when testing the 2 methods above, I could
successfully retrieve a deleted graph (empty).
Following your explanation I added a test to verify that the graph exists in
the getGraph() method.
I now see a correct behaviour. Thanks :)
I see your point about not adding graph management at the dataset level.
I was just mislead by the name removeNamedModel().
I'd recommend adding some explanation in the Javadoc so people don't make the
same assumption.
Thanks a lot,
Hubert
On Aug 23, 2014, at 1:42 AM, Andy Seaborne <[email protected]> wrote:
> Hubert,
>
> A complete, minimal example makes it much easier to answer questions or fix
> bugs.
>
> In TDB, getNamedModel will always return a Model. You can check whether it
> current exists with containsNamedModel.
>
> TDB does not track empty graphs - it just has a set of quads and a set of
> triples.
>
> containsNamedModel => there is at least one quad with the G field begin the
> URI given.
>
> Dataset ds = TDBFactory.createDataset() ;
> boolean b = ds.containsNamedModel("http://example/";) ;
> System.out.println("contains: "+b) ;
> Model m = ds.getNamedModel("http://example/";) ;
> System.out.println("Is model null?: "+(m==null)) ;
>
> Adding management of graph names would be quite a burden, impacting
> efficiency as well as complicating many application tasks.
>
> The general purpose dataset performs the role of being able to incorporate
> any model from any storage system. Adding a model is like adding to a map
> (in fact it is adding to a map!). TDB doesn't do that; adding a model is a
> copy into TDB storage.
>
> Andy
>
> On 23/08/14 05:01, Rob Vesse wrote:
>> Hubert
>>
>> Please show your actual code otherwise we can't tell what (if anything)
>> you might be doing wrong
>>
>> Also versions matter, what versions of ARQ and TDB are you using?
>>
>> Rob
>>
>> On 22/08/2014 16:52, "Hubert A Le Van Gong" <[email protected]> wrote:
>>
>>> Hello,
>>>
>>> For some reason I just can't seem to be able to completely delete a named
>>> model from a dataset...
>>>
>>> I initially thought of simply using removeNamedModel() - didn't work
>>> (model & statements still available).
>>>
>>> I've searched the mailing list and found a similar (old) thread where it
>>> was recommended to do
>>> a removeAll() which I did. This effectively empties the model but a
>>> getNamedModel() will return
>>> the Model (albeit empty).
>>> I even tried to do both removeAll() followed by a removeNameModel() but
>>> no success.
>>>
>>> In case it makes a difference, I'm using TDB.
>>>
>>> What am I doing wrong?
>
> Andy
>
>>>
>>> Cheers,
>>> Hubert
>>>
>>
>>
>>
>>
>
