I'd bluffed myself into thinking that I'd solved this but actually I
hadn't. This is my cypher:
MATCH (fromCard:Card { name: {fromCardName}}),(toCard:Card{ name:
{toCardName}})
MERGE (fromCard:Card)-[r:DECK_INCIDENCE]->(toCard:Card)
SET r.passCount = coalesce(r.passCount, 0) +1
For each pair of cards I end up creating a relationship in both directions,
for example the first time fromCard='HEARTS' and toCard='SPADES',
HEARTS->SPADES is created with passCount 1, then when fromCard='SPADES' and
toCard='HEARTS' SPADES->HEARTS is created with passCount 1. The desired
behaviour is that there is only one "bidirectional" relationship. The
direction is really not important, all I'm modelling is the strength of the
relationship i.e. the number of times that this combination of cards is
"passed" (note that I've used Hearts and Spades here purely for
explanation, I in fact have ~20k domain-specific cards)
I tried without the arrow
MATCH (fromCard:Card { name: {fromCardName}}),(toCard:Card{ name:
{toCardName}})
MERGE (fromCard:Card)-[r:DECK_INCIDENCE]-(toCard:Card)
SET r.passCount = coalesce(r.passCount, 0) +1
but that gives me: Only directed relationships are supported in CREATE,
while MATCH allows to ignore direction.
So I'm stuck here. It's important that relationships are created lazily,
i.e. the first time a 'pass' is registered, as for may pairs of cards they
will never be related at all. So how can I use the semantics of a merge to
create a relationship where the property passCount can be incremented (or
coalesced if null) regardless of the direction?
On Wednesday, February 12, 2014 12:55:19 PM UTC, Peter Neubauer wrote:
>
> Cool Ben.
>
> G: neubauer.peter
> S: peter.neubauer
> P: +46 704 106975
> L: http://www.linkedin.com/in/neubauer
> T: @peterneubauer
>
> Neo4j 2.0.0 - (graphs)-[:FOR]->(everyone)
> Kids LAN creative party in Malmö - Kidscraft ICE
>
>
> On Wed, Feb 12, 2014 at 1:45 PM, Ben Titmarsh
> <[email protected]<javascript:>>
> wrote:
> > Ah my mistake! Didn't qualify my match with the property that I was
> > matching on! This works:
> >
> > MATCH (fromCard:Card { name: {fromCardName}}),(toCard:Card{ name:
> > {toCardName}})
> >
> > MERGE (fromCard:Card)-[r:DECK_INCIDENCE]->(toCard:Card)
> > SET r.deckCount = coalesce(r.deckCount, 0) +1
> >
> > On Wednesday, February 12, 2014 11:56:32 AM UTC, Ben Titmarsh wrote:
> >>
> >> Hi Guys,
> >>
> >> I am aware that Neo4J doesn't have a concept of a bidirectional
> >> relationship and I believe that's causing me a problem when using
> MERGE.
> >> Here is my Cypher:
> >>
> >> MATCH (fromCard:Card),(toCard:Card)
> >> MERGE (fromCard:Card)-[r:DECK_INCIDENCE]->(toCard:Card)
> >> SET r.deckCount = coalesce(r.deckCount, 0) +1
> >>
> >> So say I have a collection of 4 cards:
> >> "Hearts","Diamonds","Clubs","Spades"
> >>
> >> The first time I create the relationship between Hearts and Diamonds,
> i.e.
> >> Hearts -> Diamonds. However, the next time the cards are in a
> different
> >> order and when I attempt to MERGE Diamonds -> Hearts a new relationship
> is
> >> created because no relationship exists in that direction. This is not
> what
> >> I want, I need to increment the deckCount property on the relationship
> >> regardless of the direction and don't want to have to manage two
> >> relationships per card.
> >>
> >> I cannot guarantee the order of cards and in essence I need to model a
> >> Bidirectional Relationship. How can I achieve what I need using MERGE?
> >>
> >> Cheers,
> >> Ben.
> >
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