Integrating Neo4j with Django using Custom Synchronization for Optimal Control and Reliability
Tags: neo4j, django, python, graphql
Published: 2023-08-26 11:15:02

**Introduction**

In the world of modern application development, managing complex relationships and interconnected data is a common challenge. Django, a high-level Python web framework, provides a powerful Object-Relational Mapping (ORM) system for traditional relational databases like PostgreSQL. However, when it comes to representing and querying graph data, Neo4j stands as a leading graph database. In this blog post, we'll explore how to integrate Neo4j with Django's ORM while using Neo4j's official Python driver, py2neo, and develop custom synchronization code to ensure better control and reliability.

**Why Integrate Neo4j with Django?**

Graph databases like Neo4j excel in representing highly connected data, making them ideal for scenarios such as social networks, recommendation systems, and knowledge graphs. While Django's ORM works seamlessly with relational databases, integrating Neo4j can be beneficial when the data model is inherently graph-like.

**Getting Started: Setting Up Django and Neo4j**

Django Installation: If you're new to Django, you can set it up using pip, a Python package manager:

```
pip install Django

```
Neo4j and py2neo: Install the Neo4j database and py2neo driver using pip:

```
pip install neo4j py2neo
```
Project Setup: Create a new Django project and app:

```
django-admin startproject graph_integration
cd graph_integration
python manage.py startapp graph_app
```
**Defining the Data Models**

1. In this example, let's consider a social networking scenario with users and their friendships. While user data could be stored in PostgreSQL using Django's ORM, the friendship relationships could be stored in Neo4j.

Django Models: Define the User model using Django's ORM in `graph_app/models.py`:

```
from django.db import models

class User(models.Model):
    username = models.CharField(max_length=50)
    # other fields

    def __str__(self):
        return self.username

```

2. Neo4j Nodes and Relationships: Define the User and Friendship nodes in Neo4j using py2neo. Install the neo4j database and set up a connection to it:

```
from py2neo import Graph, Node

graph = Graph("bolt://localhost:7687", user="neo4j", password="your_password")

class UserNode(Node):
    def __init__(self, username):
        super().__init__("User", username=username)

class FriendshipRelationship:
    def __init__(self, user1, user2):
        self.user1 = user1
        self.user2 = user2
        self.type = "FRIEND_OF"

```
**Synchronizing Data Between PostgreSQL and Neo4j**

To ensure consistency and reliability between the two databases, custom synchronization logic needs to be implemented.

Creating Users: When a new user is created in Django, create a corresponding UserNode in Neo4j:

```
def create_django_user_in_neo4j(sender, instance, created, **kwargs):
    if created:
        user_node = UserNode(username=instance.username)
        graph.create(user_node)

models.signals.post_save.connect(create_django_user_in_neo4j, sender=User)

```

2. Creating Friendships: When a friendship is established between Django users, create a FriendshipRelationship in Neo4j:

```
def create_neo4j_friendship(sender, instance, created, **kwargs):
    if created:
        user1_node = UserNode.select(graph, instance.user1.username).first()
        user2_node = UserNode.select(graph, instance.user2.username).first()
        if user1_node and user2_node:
            friendship = FriendshipRelationship(user1_node, user2_node)
            graph.create(friendship)

models.signals.post_save.connect(create_neo4j_friendship, sender=Friendship)

```
**Querying Data**

To query data, you'll use Django's ORM for PostgreSQL and py2neo for Neo4j.

1. Django Queries: Use Django's ORM to query user data from PostgreSQL:

```
users = User.objects.all()

```

2. Neo4j Queries: Use py2neo to query friendship data from Neo4j:

```
query = """
MATCH (user1:User)-[:FRIEND_OF]-(user2:User)
RETURN user1.username, user2.username
"""
results = graph.run(query)

```
**Conclusion**

Integrating Neo4j with Django provides a powerful solution for managing both traditional relational data and graph data within a single application. By using Neo4j's official Python driver, py2neo, and developing custom synchronization code, you can ensure better control and reliability in managing the relationships between your data. This approach allows you to harness the strengths of both databases while building a cohesive and feature-rich application.

Remember that the example provided here is a simplified demonstration. Depending on the complexity of your data model and business logic, you may need to adapt and expand the synchronization code to suit your specific requirements.