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How to manage database triggers

Because Memgraph supports database triggers on CREATE, UPDATE and DELETE operations, GQLAlchemy also implements a simple interface for maintaining these triggers.

important

This feature only works with Memgraph. Neo4j is not supported.

1. Create the trigger

To set up the trigger, first, create a MemgraphTrigger object with all the required arguments:

  • name: str ➡ The name of the trigger.
  • event_type: TriggerEventType ➡ The type of event that will trigger the execution. The options are: TriggerEventType.CREATE, TriggerEventType.UPDATE and TriggerEventType.DELETE.
  • event_object: TriggerEventObject ➡ The objects that are affected with the event_type. The options are: `TriggerEventObject.ALL, TriggerEventObject.NODEandTriggerEventObject.RELATIONSHIP`.
  • execution_phase: TriggerExecutionPhase ➡ The phase when the trigger should be executed in regard to the transaction commit. The options are: BEFORE and AFTER.
  • statement: str ➡ The Cypher query that should be executed when the trigger fires.

Now, let's create a trigger in GQLAlchemy:

from gqlalchemy import Memgraph, MemgraphTrigger
from gqlalchemy.models import (
TriggerEventType,
TriggerEventObject,
TriggerExecutionPhase,
)

db = Memgraph()

trigger = MemgraphTrigger(
name="ratings_trigger",
event_type=TriggerEventType.CREATE,
event_object=TriggerEventObject.NODE,
execution_phase=TriggerExecutionPhase.AFTER,
statement="UNWIND createdVertices AS node SET node.created_at = LocalDateTime()",
)

db.create_trigger(trigger)

The trigger names ratings_trigger will be executed every time a node is created in the database. After the transaction that created the node in question finishes, the Cypher query statement will execute, and in this case, it will set the property created_at of the newly created node to the current date and time.

2. Check the status of a trigger

You can return all of the triggers from the database with the get_Triggers() method:

triggers = db.get_triggers()
print(triggers)

3. Delete the trigger

You can use the drop_trigger() method to delete a trigger:

db.drop_trigger(trigger)