Over a million developers have joined DZone.
{{announcement.body}}
{{announcement.title}}

neo4j/cypher: CREATE with Optional Properties

DZone's Guide to

neo4j/cypher: CREATE with Optional Properties

· Java Zone ·
Free Resource

Verify, standardize, and correct the Big 4 + more– name, email, phone and global addresses – try our Data Quality APIs now at Melissa Developer Portal!

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.

Developers! Quickly and easily gain access to the tools and information you need! Explore, test and combine our data quality APIs at Melissa Developer Portal – home to tools that save time and boost revenue. 

Topics:

Published at DZone with permission of

Opinions expressed by DZone contributors are their own.

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}