Neo4j and PHP: A Powerful Combination for Graph Databases

Neo4j, a leading graph database, excels at managing highly interconnected data, making it ideal for applications involving business, social, knowledge, interest, and media graphs. This post explores Neo4j and demonstrates its use with PHP. A subsequent post will detail building a Silex-powered graph application.

Graph databases are crucial for companies dealing with complex relationships. The graph model's flexibility and graph databases' efficient storage and retrieval make them a powerful solution. Neo4j's proven ability to handle massive, interconnected datasets makes it a top choice. Its value is evident in applications like enhancing customer experiences and facilitating complex map editing.

A Quick Introduction to Graph Databases and Neo4j

A graph consists of nodes (entities) linked by relationships. In the property graph model, nodes and relationships are labeled and can have properties.

Image via Wikipedia

A graph database optimizes operations on connected data. Dedicated storage structures for nodes and relationships ensure high performance, eliminating the need for costly join operations during query execution.

Consider a social application where users follow each other. Users are represented as nodes with labels and properties.

Relationships, with types and properties, define connections between nodes, adding semantic meaning to the data.

The visual representation of this data naturally lends itself to graph databases.

Cypher: Neo4j's Query Language

Neo4j uses Cypher, a declarative query language emphasizing readability and expressiveness. Cypher focuses on what to retrieve, not how. Key clauses include:

• MATCH: Finds graph patterns.
• WHERE: Filters results.
• RETURN: Specifies the output format.
• CREATE: Creates nodes and relationships.
• MERGE: Matches existing patterns or creates new ones.

Cypher uses parentheses for nodes (e.g., (m:Movie)) and arrows for relationships (e.g., --> or -[ :LOVES ]->).

A query to retrieve Hannah Hilpert and her followers:

MATCH (user:User {name:'Hannah Hilpert'})-[r:FOLLOWS]->(follower)
RETURN user, follower

Neo4j and PHP

Neo4j runs as a server with an accessible HTTP API for querying and manipulating data. You can download Neo4j from http://ipnx.cn/link/25989f1da5598dd89e7134affeca8697 or use a service like GrapheneDB. The Neo4j Browser (http://ipnx.cn/link/0806a60e2e5466094ab2652bef28a251) provides a visual interface.

Neoxygen Components

Neoxygen offers open-source PHP components for interacting with Neo4j. NeoClient provides a robust client for the Neo4j HTTP API.

Installation and Configuration

Add the neoclient dependency to your composer.json:

{
  "require": {
    "neoxygen/neoclient":"~2.1"
  }
}

Configure the connection:

use Neoxygen\NeoClient\ClientBuilder;

$client = ClientBuilder::create()
  ->addConnection('default', 'http', 'localhost', 7474)
  ->build();

For GrapheneDB, use a secure connection:

<?php
use Neoxygen\NeoClient\ClientBuilder;

$connUrl = parse_url('http://master.sb02.stations.graphenedb.com:24789/db/data/');
$user = 'master';
$pwd = 's3cr3tP@ssw0rd';

$client = ClientBuilder::create()
  ->addConnection('default', $connUrl['scheme'], $connUrl['host'], $connUrl['port'], true, $user, $password)
  ->build();

Enable automatic response formatting:

$client = ClientBuilder::create()
  ->addConnection('default', 'http', 'localhost', 7474)
  ->setAutoFormatResponse(true)
  ->build();

Building a Sample Application

Let's create users and FOLLOWS relationships. A CREATE query:

CREATE (user:User {name:'Kenneth'}) RETURN user

PHP code to create a user:

$query = 'CREATE (user:User {name:"Kenneth"}) RETURN user';
$result = $client->sendCypherQuery($query)->getResult();
$user = $result->getSingleNode();
$name = $user->getProperty('name');

Creating a relationship:

$query = 'MATCH (user1:User {name:{name1}}), (user2:User {name:{name2}}) CREATE (user1)-[:FOLLOWS]->(user2)';
$params = ['name1' => 'Kenneth', 'name2' => 'Maxime'];
$client->sendCypherQuery($query, $params);

Using Graphgen to create multiple users and relationships simplifies the process. Import the generated graph into your database.

A Cypher query for friendship suggestions:

MATCH (user:User {firstname: {firstname}})-[:FOLLOWS]->(followed)-[:FOLLOWS]->(suggestion)
WHERE user <> suggestion
  AND NOT (user)-[:FOLLOWS]->(suggestion)
RETURN user, suggestion, count(*) as occurrence
ORDER BY occurrence DESC
LIMIT 10

Conclusion

This post introduced graph databases, Neo4j, and Cypher, showing how to use Neo4j with PHP. The next post will build a complete Silex application. The provided FAQs offer further details and best practices.

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