Apoc Trigger in "Phase: After" Never Ends

[neo-technology-build-agent]

Issue by leandrogalrinho
Thursday Mar 19, 2020 at 16:10 GMT
Originally opened as neo4j-contrib/neo4j-apoc-procedures#1453

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Hello,
I've ran into an unexpected behavior and can't figure out what's the source of it. I'm using apoc 3.5.0.9, and I'm trying to have a trigger in "phase: after" that creates a relationship with the node that has been updated with some other node, but this causes the trigger to never end. However, if the trigger is in "phase: before" it all goes as expected.

Expected Behavior

The trigger is supposed to catch the update event and, after the transaction that updates the _executed property commits, it creates a new relationship with the updated node and a new node.

Actual Behavior

However, unless I terminate the query this never seems to end and will leave the graph in the same state it was before the update, except that the _executed property was indeed updated... But neither the node or the new relation is created.

How to Reproduce the Problem

Simple Dataset

CREATE (:TEST {name:'x', _executed:0});
CREATE (:TEST {name:'y', _executed:0});

CALL apoc.trigger.add('triggerTest','UNWIND apoc.trigger.propertiesByKey({assignedNodeProperties},"_executed") as prop
	WITH prop.node as n
	CREATE (z:SON {father:id(n)})
	CREATE (n)-[:GENERATED]->(z)',
{phase:'after'});

Steps

1. Insert dataset and trigger into neo4j.
2. Perform this simple query that updates the _executed property of node x, activating the trigger:

MATCH (a:TEST)
WHERE a.name = 'x'
SET a._executed = a._executed+1

Specifications (Mandatory)

Currently used versions

Versions

• OS: Windows 8.1
• Neo4j: 3.5.14 Enterprise
• Neo4j-Apoc: 3.5.0.9

[neo-technology-build-agent]

Comment by hikemachado
Tuesday May 05, 2020 at 18:35 GMT

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I`m facing similar issue.
I have a trigger for create relationship, in this trigger I need to create another relationship (but different relationship type) for the node.
every time it is triggered for the specific relationshiptype it never ends

trigger definition:

CALL apoc.trigger.add("Cluster_TRG", 
'UNWIND [rel in {createdRelationships} WHERE type(rel) = "IN_CLUSTER"] AS r with r, startNode(r) as nn, endNode(r) as cn match (cn)<-[]-(b) where id(b) <> id(nn)  with nn, b  match (b)-[outR:Depends_On]->(p) with nn, b,  outR, p create (nn)-[nr:Depends_On]->(p) with p call apoc.log.info("Triggert called " + p.Name) return null',
{phase:'after'})

Versions

• OS : Windows 10
• Neo4j : 3.5.5 Community
• Neo4j-Apoc: 3.5.0-11

[neo-technology-build-agent]

Comment by saibhaskerraju
Monday Jun 22, 2020 at 13:36 GMT

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Hi All,
Sincere apologies if this doesn't make sense
I created the below trigger

CALL apoc.trigger.add('increase_followings_and_followers',
'UNWIND $createdRelationships AS rel 
WITH rel, STARTNODE(rel) as follower, ENDNODE(rel) AS followed WITH rel, follower, followed
WHERE TYPE(rel)="HAS_E"
SET follower.followings = 1, followed.followers= 2',
{phase:'before'})

and this is the basic query I am writing

match(p:Post{id:1}) create(c:Comment{id:354}) merge(c)-[:HAS_E]->(p)

I have two scenarios
CASE 1: The Phase in trigger = ' after'
I see new :comment node getting created and attached to :Post node but the query doesn't stop. it keeps on looping
CASE 2: Phase in trigger = ' before '
I don't see new :Comment node not relationship to :Post but query doesn't stop. it keeps on looping

I am running version 4.0.6 and apoc 4.0.0.15

Can someone please let me know what I am missing here.

[neo-technology-build-agent]

Comment by jexp
Tuesday Aug 04, 2020 at 22:51 GMT

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@conker84 could you have a look at this?

[neo-technology-build-agent]

Comment by magaton
Monday Jun 07, 2021 at 13:20 GMT

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I have exactly the same problem.
Neo4j 4.2.4, apoc, 4.2.0.4
When I run cypher within trigger, all is good, the same applies when trigger is set with phase:'before', but it never completes with phase: 'after'.

[neo-technology-build-agent]

Comment by vga91
Wednesday Jun 30, 2021 at 07:34 GMT

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@leandrogalrinho
With the latest Apoc version there is a phase: "afterAsync" to prevent some Transaction errors like this.
Please, could you try with this?