Hello again guys,
with this query i get a list of nodes ordered by date. I need to create a relationship named "SEQUENCE" between each result, so the 1st is connected to the 2nd, the 2nd to the 3rd and so on.
How can i do that just by using cypher ?
MATCH (pg1:Perception_Group)
RETURN pg1.date
ORDER BY pg1.date ASC
trying this one from Mark Needham's website (Neo4j: Cypher - Creating relationships between a collection of nodes / Invalid input '[': | Mark Needham), but not working (getting "Error occurred: Type mismatch: expected Path but was List (line 5, column 30 (offset: 106)) "FOREACH(i in RANGE(0, length(pgs)-2) |" ^)
MATCH (pg:Perception_Group)
WITH pg
ORDER BY pg.date
WITH COLLECT(pg) AS pgs
FOREACH(i in RANGE(0, length(pgs)-2) |
FOREACH(pg1 in [pgs[i]] |
FOREACH(pg2 in [pgs[i+1]] |
CREATE UNIQUE (pg1)-[:SEQUENCE]->(pg2))))
Well. made these changes and it is working. Any suggestions ?
MATCH (pg:Perception_Group)
WITH pg
ORDER BY pg.date
WITH COLLECT(pg) AS pgs
FOREACH(i in RANGE(0, size(pgs)-2) |
FOREACH(pg1 in [pgs[i]] |
FOREACH(pg2 in [pgs[i+1]] |
MERGE (pg1)-[:SEQUENCE]->(pg2))))
Hello there,
I recreated your test and it is working indeed. Not sure if you still expect suggestions (as you asked), or it was a typo...
Anyway, as Mark already explained, the (still) necessary hack here is with the two intermediate FOREACH clauses. What each of them does is simply access a list element and return it as a node. This is because MERGE (or CREATE) do not accept indexed list items in their patterns, just nodes.
Hope it helps,
Chris
Hi Chris,
thank you for your comment and for taking the time to recreate my test. It made me understand better the trick involved.
I always need other people's comments or suggestions, because with them i am able to learn cypher faster by getting all the tips and insights you guys share 
Also i am always concerned with performance and everyone's comments may show me better ways to do queries.
Cheers
José Salvador