Neo4j- questions on Syntax apoc trigger

问题

I have the following APOC trigger which contains a apoc procedure. This works as desired but I am wondering if I used a lot of WITH statements, is that the way to go? or is there a better way to refactor this code. I am still new to neo4j so not sure.

The control flow- Whenever the Enrollment node is created, it creates an SPerson node and depending on the size(number of SPerson nodes) it creates an enrolled or waitlist(if size>3, and deletes enrolled relation) relation with the course node.

CALL apoc.trigger.add('loadEnrollments',   
"UNWIND apoc.trigger.nodesByLabel($assignedLabels, 'Enrollment') AS node
 MERGE (p1:SPerson { name: node.name, cell: node.cell, created_at: node.created_at})
 WITH p1, node
 MATCH (c:Course {name: 'Paradigm Shifting 101'})
 WITH node
 MATCH (n:SPerson)
 WITH node, COUNT(n) as size
 CALL apoc.do.when(
 size>3,
 'MATCH(p1:SPerson),(c:Course) 
 WHERE p1.name=node.name
 CREATE (p1)-[:Waitlist]->(c)
 WITH p1,c 
 MATCH (e:Enrollment) DETACH DELETE e',
 'MATCH(p1:SPerson),(c:Course) 
 WHERE p1.name=node.name
 CREATE (p1)-[:Enrolled]->(c)
 WITH p1,c 
 MATCH (e:Enrollment) DETACH DELETE e', {node:node}) YIELD value
 DETACH DELETE node", 
 
 { phase: 'after' });

回答1:

You should:

minimize the number of rows of data that have to be processed for a query, and
not repeat operations unnecessarily.

With those rules in mind, this query may work (efficiently) for you:

CALL apoc.trigger.add(
  'loadEnrollments',
  "
  CALL apoc.cypher.doIt('MATCH (e:Enrollment) DETACH DELETE e', {}) YIELD value
  WITH value
  MATCH (n:SPerson)
  WITH COUNT(n) as size
  MATCH (c:Course {name: 'Paradigm Shifting 101'})
  UNWIND apoc.trigger.nodesByLabel($assignedLabels, 'Enrollment') AS node
  MERGE (p1:SPerson {name: node.name, cell: node.cell, created_at: node.created_at})
  DETACH DELETE node
  CALL apoc.create.relationship(p1, CASE WHEN size > 3 THEN 'Waitlist' ELSE 'Enrolled' END, {}, c) YIELD rel
  ",
  { phase: 'after' }
);

来源：https://stackoverflow.com/questions/62943204/neo4j-questions-on-syntax-apoc-trigger

标签

neo4j

cypher

neo4j-apoc