Thanks for the reply.
What's funny is I have an identical piece of code that uses
Iterator<Node> neo4jNodeList = theDB.findNodes(newLabel);
instead of
Iterator<Node> neo4jNodeList = theDB.findNodes(newLabel, key, value);
and it works fine. Everything else is the same and the getNext code is
the same call. So maybe there is something wrong with the second call to
findNodes.
Very strange ...
Howard
On 8/19/16 4:13 PM, 'Michael Hunger' via Neo4j wrote:
You have to iterate inside the or at least a transaction
Von meinem iPhone gesendet
Am 19.08.2016 um 20:25 schrieb Howard Lander <[email protected]
<mailto:[email protected]>>:
Hi all
Hi all
Thanks in advance for the attention and any suggestions. I hope my
explanation of the issue is clear enough.
As noted in the subject line, I'm upgrading my java based project to
Version 3 of the embedded API. Unfortunately, I'm getting the
following error:
SEVERE: exception in hasNext: The statement has been closed.
Code is below, but here's the explanation. In order to provide a
layer of isolation in between my application code and the database
code (in this case Neo4j), I'm using the DAO pattern. I'm assigning
the ResourceIterator I'm getting back from the findNodes call to a
variable in the user level iterator I'm defining. According to this
page
(https://neo4j.com/docs/java-reference/current/javadocs/org/neo4j/graphdb/Transaction.html)
"All |ResourceIterables|
<https://neo4j.com/docs/java-reference/current/javadocs/org/neo4j/graphdb/ResourceIterable.html> that
where returned from operations executed inside a transaction will be
automatically closed when the transaction is committed or rolled
back. Note however, that the |ResourceIterator|
<https://neo4j.com/docs/java-reference/current/javadocs/org/neo4j/graphdb/ResourceIterator.html> should
be |closed|
<https://neo4j.com/docs/java-reference/current/javadocs/org/neo4j/graphdb/ResourceIterator.html#close--> as
soon as possible if you don't intend to exhaust the iterator"
That's clear enough and seems to explain why I am getting the
exception. But there has to be some way to return an iterator for
later use. At least I hope so. The other choice that comes to mind
would be to store all of the nodes in user memory so my user level
interface can iterate through them, and that would be a bit
problematic. I'll note that this code (which used to use the
GlobalGraphOperations class) worked in Neo4j 2. but maybe that was a
bug in Neo4j 2? Note that I have tried not closing the transaction
(or even using a transaction at all).
Any ideas?
Here's the actual source of the problem: It's in my definition of an
iterator for the user visible structure representing nodes.
public boolean hasNext() {
// Wrap the neo4j iterator
boolean hasN = false;
GraphDatabaseService theDB =
Neo4jDAOFactory.getTheNetworkDB();
Transaction tx = theDB.beginTx();
try {
hasN = nodeIterator.hasNext();
} catch (Exception e) {
// should send this back using the message logs eventually
this.logger.log (Level.SEVERE, "exception in hasNext:
" + e.getMessage(), e);
} finally {
tx.close();
}
return hasN;
}
But it doesn't make sense without also looking at:
public Iterator<NetworkNodeTransferObject>
getNetworkNodes(String nameSpace, String key, Object value){
Neo4jNetworkNodeDAOIterator theIterator = null;
GraphDatabaseService theDB = Neo4jDAOFactory.getTheNetworkDB();
Transaction tx = theDB.beginTx();
try {
Label newLabel = Label.label(nameSpace);
Iterator<Node> neo4jNodeList = theDB.findNodes(newLabel,
key, value);
theIterator = new Neo4jNetworkNodeDAOIterator();
theIterator.nodeIterator = neo4jNodeList;
} catch (Exception e) {
// should send this back using the message logs eventually
this.logger.log (Level.SEVERE, "exception in
getNetworkNodes: " + e.getMessage(), e);
} finally {
tx.close();
}
return theIterator;
}
Thanks
Howard
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Howard Lander <mailto:[email protected]>
Senior Research Software Developer
Renaissance Computing Institute (RENCI) <http://www.renci.org>
The University of North Carolina at Chapel Hill
Duke University
North Carolina State University
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