trigger_write_write_conflict

Write-write conflict with Memgraph triggers demonstration

This example demonstrates how to use Memgraph triggers (both BEFORE COMMIT and AFTER COMMIT) with the Neo4j Python driver (neo4j) to simulate real-world data mutation and side-effects using concurrent transactions.

🧠 What This Example Does

The script performs the following actions:

1. Connects to a running Memgraph instance using the Neo4j Python driver.

2. Creates a global node that serves as the target of trigger-generated relationships.

3. Creates a BEFORE COMMIT trigger that automatically creates an edge from every newly created node to the global node.

4. Uses two separate sessions to simulate concurrent transactions:

   • One modifies the global node in a transaction that remains open.
   • The other creates a node to test whether the trigger can access the global node (it can't if it's uncommitted).

5. Drops the BEFORE COMMIT trigger, then repeats the same process with an AFTER COMMIT trigger.

6. Validates the behavior of both trigger types by reading relationships created in the graph.

🚀 How to Run Memgraph with Docker

To run Memgraph Enterprise using Docker:

docker run -it --rm -p 7687:7687 memgraph/memgraph:3.2.0

🛠 Requirements

Install the required Python dependency with:

pip install neo4j

Your requirements.txt should include:

neo4j

🧪 How to Run the Script

Make sure Memgraph is running, then execute:

python3 memgraph_trigger_demo.py

🔁 Trigger Behavior

• BEFORE COMMIT triggers:

  • Run inside the same transaction that caused the event.
  • Cannot see changes made in uncommitted transactions (i.e., isolation applies).

• AFTER COMMIT triggers:

  • Run after the original transaction commits.
  • Can access the full committed graph state.

This script showcases both trigger types and how transaction isolation affects their behavior.

📂 File Structure

memgraph_trigger_demo.py    # Python script that sets up and tests triggers
requirements.txt            # Python dependencies
README.md                   # This file

🔖 Version Compatibility

Tested with:

• Memgraph v3.2
• Neo4j Python Driver v5.16.0+

🏢 Enterprise or Community?

This example works with Memgraph Community Edition.

💬 Need Help?

Reach out to us on the Memgraph Discord server — we’re happy to help!