Add constraints to neo4j node based on node property value

Question

I am adding constraints to a neo4j database using Cypher constraints and want to create a constraint which only applies to a subset of a node type.

I can create a constraint that a foo field must exist on Entity with

CREATE CONSTRAINT ON (e:Entity) ASSERT EXISTS (e.foo)

but instead, I want to constrain only nodes with a given field. e.g

CREATE CONSTRAINT ON (e:Entity {constrain_flag:true) ASSERT EXISTS (e.foo)

For example, I may have two nodes like

(e:Entity { foo: 'bar' , constrain_flag: true }) and

(e:Entity { constrain_flag: false })

I only want the constraint that e.foo must exist to apply to the Entity where constrain_flag = true, so both of these should be allowed. However,

(e:Entity { constrain_flag: false }) should throw an exception.

Is there a way to do this currently with cypher and neo4j?

Thanks in advance!

cybersam cybersam · Accepted Answer · 2020-05-29T16:16:26

Instead of adding a flag property, you can just add an additional label (say, ConstrainedEntity) to Entity nodes that should be constrained. Queries can continue to use just the Entity label.

For example:

CREATE CONSTRAINT ON (ce:ConstrainedEntity) ASSERT EXISTS (ce.foo)

To create a "flagged" Entity:

CREATE (e:Entity:ConstrainedEntity {id: 111, foo: 'bar'})

To "flag" an existing Entity:

MATCH (e:Entity)
WHERE e.id = 123
SET e:ConstrainedEntity

Add constraints to neo4j node based on node property value

1 Answers