apoc.lock.nodes

Procedure APOC Core

apoc.lock.nodes([nodes]) acquires a write lock on the given nodes

Signature

apoc.lock.nodes(nodes :: LIST? OF NODE?) :: VOID

Input parameters

Name	Type	Default
nodes	LIST? OF NODE?	null

Name

Type

Default

nodes

LIST? OF NODE?

null

Usage Examples

The examples in this section are based on the following sample graph:

CREATE (:Person {name:'Alex'})
CREATE (:Email {address:'alex@somewhere.com'});

We want to create exactly one HAS_EMAIL relationship between these nodes. We can use the MERGE clause to help us do this, but the MERGE clause isn’t thread safe, so we could have a situation where two nodes write the HAS_EMAIL relationship at the same time.

We can prevent this race condition by using the apoc.lock.nodes procedure, as shown below:

MATCH (p:Person {name:'Alex'})
MATCH (e:Email {address:'alex@somewhere.com'})
CALL apoc.lock.nodes([p,e])
MERGE (p)-[rel:HAS_EMAIL]->(e)
RETURN rel;

Table 1. Results
rel
[:HAS_EMAIL]