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?	{}

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?

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
apoc.trigger.refresh=60000

Table 1. Description
Option Key	Value	Description
apoc.trigger.enabled	true/false, default false	Enable/Disable the feature
apoc.trigger.refresh	number, default 60000	Interval in ms after which a replication check is triggered across all cluster nodes

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 2. 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 3. Results
count
1