NoSQL Zone is brought to you in partnership with:

Mark is a graph advocate and field engineer for Neo Technology, the company behind the Neo4j graph database. As a field engineer, Mark helps customers embrace graph data and Neo4j building sophisticated solutions to challenging data problems. When he's not with customers Mark is a developer on Neo4j and writes his experiences of being a graphista on a popular blog at http://markhneedham.com/blog. He tweets at @markhneedham. Mark is a DZone MVB and is not an employee of DZone and has posted 553 posts at DZone. You can read more from them at their website. View Full User Profile

neo4j/cypher: CREATE with Optional Properties

06.22.2013
| 4159 views |
  • submit to reddit

I’ve written before about using the cypher CREATE statement to add inferred information to a neo4j graph and sometimes we want to do that but have to deal with optional properties while creating our new relationships.

For example let’s say we have the following people in our graph with the ‘started’ and ‘left’ properties representing their tenure at a company:

CREATE (person1 { personId: 1, started: 1361708546 })
CREATE (person2 { personId: 2, started: 1361708546, left: 1371708646 })
CREATE (company { companyId: 1 })

We want to create a ‘TENURE’ link from them to the company including the ‘started’ and ‘left’ properties when applicable and might start with the following query:

START person = node:node_auto_index('personId:1 personId:2'), 
      company = node:node_auto_index('companyId:1') 
CREATE person-[:TENURE_AT { started: person.started, left: person.left }]-company 
RETURN person, company

which throws an exception because not all people have a ‘left’ property:

Error: org.neo4j.cypher.EntityNotFoundException: The property 'left' does not exist on Node[1]

We tweak our query a bit to make the property optional:

START person = node:node_auto_index('personId:1 personId:2'), 
      company = node:node_auto_index('companyId:1') 
CREATE person-[:TENURE_AT { started: person.started, left: person.left? }]-company 
RETURN person, company

which still doesn’t work:

Error: java.lang.IllegalArgumentException: Null parameter, key=left, value=null

After looking at this for a while Alistair pointed out that we should just split the updating of the optional property from the creation of the relationship so we end up with the following:

START person = node:node_auto_index('personId:1 personId:2'), 
      company = node:node_auto_index('companyId:1') 
CREATE person-[tenure:TENURE_AT { started: person.started }]-company 
WITH person, tenure, company
WHERE HAS(person.left)
SET tenure.left = person.left 
RETURN person, company

The code is on the console if you want to see how it works.

Published at DZone with permission of Mark Needham, author and DZone MVB. (source)

(Note: Opinions expressed in this article and its replies are the opinions of their respective authors and not those of DZone, Inc.)