Thanks Craig,
I'd like to clarify my question (I don't think it changes your answer
though).
I wanted all messages visible to me created by users I follow. Thus, the
FOLLOWS relationship is not enough. I'd need to see messages that are
visible to me and then check if they were created by users I follow, or I'd
need to see messages created by users I follow and then see if they're
visible to me.
I assume your last example still yields the result I'm looking for. Could
you describe what actually happens here though? I'm unclear on what the
traversal looks like. Would it first traverse every outgoing FOLLOWS
relationship from the viewer, yielding other users, and then traverse all
the CREATED relationships to get to messages?
Also, given very large numbers of FOLLOWS and CREATED relationships (with
say, a twitter graph), how is this made efficient?
Sorry for all the basic questions but I couldn't find this information in
the docs. If there's something I should be reading before posting these
questions, please point me to it.
Thanks!
Lincoln
On Wed, Mar 17, 2010 at 7:06 AM, Craig Taverner <cr...@amanzi.com> wrote:
> I'm uncertain about one ambiguity in your model, you are able to find
> messages through FOLLOWS and IS_VISIBLE_BY. These will give two different
> sets, and my first impression was that FOLLOWS gives you the right answer.
> In other words you want to query for 'all messages by users I follow'? In
> that case you do not need IS_VISIBLE_BY. However, if there are messages by
> people you follow, but are not allowed to see, then you also need the
> IS_VISIBLE_BY. But I would still reconsider linking directly from the
> viewer
> to the message for that case. I'd rather have the messages linked to some
> categorization structure for things like 'public', 'private', etc.
>
> Anyway, here are some suggestions for the various approaches above:
> *'all messages by users I follow'*
> val msgs = viewer.traverse(
> Order.BREADTH_FIRST, StopEvaluator.END_OF_GRAPH,
> (tp: TraversalPosition) => IsMessage(tp.currentNode()),
> Rels.FOLLOWS, Direction.OUTGOING,
> Rels.CREATED, Direction.OUTGOING)
>
> *'all messages visible to me'*
> val msgs = viewer.traverse(
> Order.BREADTH_FIRST, StopEvaluator.END_OF_GRAPH,
> ReturnableEvaluator.ALL_BUT_START_NODE,
> Rels.IS_VISIBLE_BY, Direction.INCOMING)
>
> *'all messages, visible to me, by people I follow'*
> val msgs = viewer.traverse(
> Order.BREADTH_FIRST, StopEvaluator.END_OF_GRAPH,
> (tp: TraversalPosition) => {
> val msg = tp.currentNode()
> IsMessage(msg) && IsVisibleBy(msg,viewer)
> },
> Rels.FOLLOWS, Direction.OUTGOING,
> Rels.CREATED, Direction.OUTGOING)
>
> Of course I assume you make the utility functions IsMessage(node: Node) and
> IsVisibleBy(msg: Node, user: Node), and these will test the existance of
> properties and relations as appropriate to make the decision.
>
>
> On Wed, Mar 17, 2010 at 6:32 AM, Lincoln <linxbet...@gmail.com> wrote:
>
> > Hi, I've just started looking at Neo4j and I'm quite intrigued. However,
> > the cognitive dissonance that I've grown so used to in modeling storage
> is
> > proving to be a bit difficult to let go at this early stage :)
> >
> > I was hoping that if someone could help me through an example I would be
> > able to grok how to properly structure my data and query it in Neo4j.
> >
> > Nodes:
> > Message( text: String )
> > User( id: Long )
> >
> > Relationships:
> > CREATED
> > FOLLOWS
> > IS_VISIBLE_BY
> >
> > So I might have a graph with entries like so:
> >
> > User(1) --> CREATED --> Message("i woke up late today")
> > User(2) --> CREATED --> Message("hello")
> > User(3) --> CREATED --> Message("ugh, i hate mondays")
> >
> > User(1) --> FOLLOWS --> User(2)
> >
> > Let's also say all messages are visible to User 1.
> >
> > Message("i woke up late today") --> IS_VISIBLE_BY --> User(1)
> > Message("hello") --> IS_VISIBLE_BY --> User(1)
> > Message("ugh, i hate mondays") --> IS_VISIBLE_BY --> User(1)
> >
> > So, I can do a simple traversal for visible:
> >
> > val graphDb = new EmbeddedGraphDatabase( "path/to/neo4j-db" )
> > val index = new LuceneIndexService( graphDb )
> > val viewer = index.getSingleNode("id", 1)
> > val msgs = viewer.traverse( Order.BREADTH_FIRST,
> > StopEvaluator.END_OF_GRAPH,
> > ReturnableEvaluator.ALL_BUT_START_NODE, Rels.IS_VISIBLE_BY,
> > Direction.INCOMING)
> > msgs.toList.map(_.toJson).mkString("{ msgs : [", ",", "] }") // assuming
> i
> > have the relevant functions
> >
> > But let's say that this is going to return too many messages. Just
> because
> > all the messages are possibly visible to me, doesn't mean I want to see
> > them
> > all. So, I'd like to additionally filter by the FOLLOWS relationship.
> I'd
> > like to express "get all messages that are visible and were created by a
> > user that I follow." Can someone show me an example of how to do that?
> >
> > I'm guessing that you need to implement a custom ReturnableEvaluator, but
> I
> > don't understand how you traverse multiple relationships at the same
> time.
> >
> > Thanks,
> > Lincoln
> > _______________________________________________
> > Neo mailing list
> > User@lists.neo4j.org
> > https://lists.neo4j.org/mailman/listinfo/user
> >
> _______________________________________________
> Neo mailing list
> User@lists.neo4j.org
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>
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