Triggers

Overview

A trigger is a mechanism that automatically executes predefined operations in response to specific events on nodes or edges. Triggers can be set to run before or after events such as insertion, update, or deletion of data. They allow you to enforce business rules, maintain data integrity, or perform auxiliary operations without manual intervention, ensuring that logic tied to DML operations is executed consistently and automatically.

Showing Triggers

To show triggers in the current graph:

SHOW TRIGGER

To show node triggers in the current graph:

SHOW NODE TRIGGER

To show edge triggers in the current graph:

SHOW EDGE TRIGGER

Each trigger provides the following essential metadata:

Creating Trigger

To create a trigger AutoUpperCase for Student nodes that converts the name property to uppercase before insertion:

CREATE TRIGGER "AutoUpperCase" ON NODE "Student" 
COMMENT "Converts name to uppercases before insertion" 
BEFORE INSERT CALL "
  $entity CALL {
    LET entity.name = upper(entity.name)
  }
"

This trigger automatically converts the name property of a Student node to uppercase before insertion:

INSERT (n:Student {name: "John Doe"}) RETURN n.name

Result:

To create a trigger AutoStaus for ENROLLED_IN edges, automatically setting the status property to "active" before insertion:

CREATE TRIGGER "AutoStaus" ON EDGE "ENROLLED_IN"
COMMENT "Sets status to true"
BEFORE INSERT CALL "
  $entity CALL {
    LET entity.status = 'active'
  }
"

This trigger automatically sets the status property of an ENROLLED_IN edge to "active" before insertion:

MATCH (s:Student {name: "JOHN DOE"}), (c:Course {name: "Science"})
INSERT (s)-[e:ENROLLED_IN]->(c)
RETURN e.status

Result:

Dropping Trigger

To drop the node trigger AutoUpperCase:

DROP NODE TRIGGER AutoUpperCase

To drop the edge trigger AutoStaus:

DROP EDGE TRIGGER AutoStaus

Note: Dropping a node or edge schema will also remove any triggers associated with that schema.