是否可以检索RDF4J事务的更新语句

Question

我正在努力支持"干式运行"；SPARQL上的功能使用RDF4J更新查询。我想通知用户将要插入/删除的语句，最好是从当前事务中获取语句。我在想：

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.");

有没有办法用RDF4J做到这一点？

Answer 1

(从https://github.com/eclipse/rdf4j/discussions/3163(

你可以用SailConnectionListener做一些类似的事情。不过，访问这个的方式有点笨拙。这里有一个例子：

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");
}

正如您所看到的，我们需要将RepositoryConnection强制转换为特定类型以检索底层SailConnection，然后我们还需要将该SailConnection强制转换为NotifyingSailConnection，以便能够在其上注册SailConnectionListener。此侦听器将接收单个语句的预提交添加和删除事件。运行上述代码将产生以下控制台输出：

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