I am trying to support "dry run" functionality on SPARQL update queries using RDF4J. I want to inform the user of the statements that will be inserted/deleted, ideally by getting the statements from the current transaction. I'm thinking something like:
conn.begin();
Update query = conn.prepareUpdate(queryString);
query.execute();
// Print statements in the transaction
System.out.println("Dry run completed.");
conn.rollback();
System.out.println("Dry run rolled back.");
Is there a way to do this with RDF4J?
(copied from https://github.com/eclipse/rdf4j/discussions/3163 )
You can do something along those lines with a SailConnectionListener
. The way to access this is a little bit clunky though. Here's an example:
Repository rep = new SailRepository(new MemoryStore());
try (SailRepositoryConnection conn = (SailRepositoryConnection) rep.getConnection()) {
NotifyingSailConnection sailConn = (NotifyingSailConnection) conn.getSailConnection();
sailConn.addConnectionListener(new SailConnectionListener() {
@Override
public void statementRemoved(Statement removed) {
System.out.println("removed: " + removed);
}
@Override
public void statementAdded(Statement added) {
System.out.println("added: " + added);
}
});
conn.begin();
conn.add(FOAF.PERSON, RDF.TYPE, RDFS.CLASS);
String update = "DELETE { ?p a rdfs:Class } INSERT { ?p rdfs:label \"Person\" } WHERE { ?p a rdfs:Class }";
conn.prepareUpdate(update).execute();
System.out.println("executed");
conn.rollback();
System.out.println("transaction aborted");
}
As you can see we need to cast the RepositoryConnection
to a specific type to retrieve the underlying SailConnection
, and then we further need to cast that SailConnection
to a NotifyingSailConnection
to be able to register a SailConnectionListener
on it. This listener will receive pre-commit added and removed events for individual statements. Running the above code would produce the following console output:
added: (http://xmlns.com/foaf/0.1/Person, http://www.w3.org/1999/02/22-rdf-syntax-ns#type, http://www.w3.org/2000/01/rdf-schema#Class)
removed: (http://xmlns.com/foaf/0.1/Person, http://www.w3.org/1999/02/22-rdf-syntax-ns#type, http://www.w3.org/2000/01/rdf-schema#Class) [null]
added: (http://xmlns.com/foaf/0.1/Person, http://www.w3.org/2000/01/rdf-schema#label, "Person")
executed
transaction aborted