apoc.trigger.add

Procedure APOC Core

add a trigger kernelTransaction under a name, in the kernelTransaction you can use {createdNodes}, {deletedNodes} etc., the selector is {phase:'before/after/rollback'} returns previous and new trigger information. Takes in an optional configuration.

Signature

apoc.trigger.add(name :: STRING?, kernelTransaction :: STRING?, selector :: MAP?, config = {} :: MAP?) :: (name :: STRING?, query :: STRING?, selector :: MAP?, params :: MAP?, installed :: BOOLEAN?, paused :: BOOLEAN?)

Input parameters

Name Type Default

name

STRING?

null

kernelTransaction

STRING?

null

selector

MAP?

null

config

MAP?

{}

Output parameters

Name Type

name

STRING?

query

STRING?

selector

MAP?

params

MAP?

installed

BOOLEAN?

paused

BOOLEAN?

Enable Triggers

By default triggers are disabled. We can enable them by setting the following property in apoc.conf:

apoc.conf
apoc.trigger.enabled=true

Usage Examples

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

CREATE (:Counter {count:0})
CREATE (f:Foo);

Let’s create a trigger that keeps a count of the number of nodes that have been deleted:

CALL apoc.trigger.add(
  'count-removals',
  'MATCH (c:Counter)
   SET c.count = c.count + size([f IN $deletedNodes WHERE id(f) > 0])',
  {}
);
Table 1. Results
name query selector params installed paused

"count-removals"

MATCH (c:Counter) SET c.count = c.count + size([f IN $deletedNodes WHERE id(f)  0])

{}

{}

TRUE

FALSE

We’ll now delete the Foo node:

MATCH (f:Foo)
DELETE f;
Results
0 rows available after 20 ms, consumed after another 0 ms
Deleted 1 nodes

And finally, let’s check that the count property on our Counter node has been incremented:

MATCH (c:Counter)
RETURN c.count as count;
Table 2. Results
count

1