Graph database tutorial

Neo4j, a most popular Graph database

This article shares very first step of Graph database tutorial for beginners.

Sample code

https://github.com/maclt/sample-graphdb

Overview

Glossary

Neo4j … open-source graph database management system designed to store, query, and manage data in the form of graphs. Neo4j graph database is composed of 2 concepts.

1. Node … an entity or object in the graph.

2. Relationship … connects two nodes and represents the relationship or association between them. ¹

Cypher Query Language (CQL)² … a declarative query language similar to SQL but designed for graph databases.

Prerequisites

• Go 1.23.3

• Docker or equivalent

Step 1. Prepare Docker image

Download docker image and run the container³

$ docker pull neo4j

$ docker run \
    --publish=7474:7474 --publish=7687:7687 \
    --volume=$HOME/neo4j/data:/data \
    neo4j

Neo4j has GUI called Neo4j Browser⁴. Once you started the docker container, you can access to http://localhost:7474/browser/ .

The default username is “neo4j”.

On the Neo4j browser, you can set up the password for the database. In the sample code, the password is “password”.

Step 2. Initiate Gin

In this article I do NOT explain about Gin. Please refer the official document by Gin⁵.

If you are not familiar with Gin, here I share 2 commands to start the server.

$ go mod download // download the packages

$ go run main.go // run the server which exposes REST API

Step 3. Dependency Injection for DB Connection

In mod.go file, you see a neo4j-go-driver (link) which enable the Gin server to connect to the Neo4j database.

📄 mod.go

module maclt/graphdb/neo4j

go 1.23.3

require (
	...
	github.com/neo4j/neo4j-go-driver/v5 v5.27.0 // indirect
        ...
)

With neo4j-go-driver, the dependency injection struct is implemented in database/database.go file.

📄 database/database.go

package database

import (
	"context"
	"log"

	"github.com/neo4j/neo4j-go-driver/v5/neo4j"
)

type DatabaseDriver struct {
	Driver neo4j.DriverWithContext
}

// Constructor function to create a new database driver instance
func Connect() *DatabaseDriver {
	uri := "bolt://localhost:7687" // Bolt protocol
	username := "neo4j"
	password := "password"

	// Create a driver instance
	driver, err := neo4j.NewDriverWithContext(uri, neo4j.BasicAuth(username, password, ""))
	if err != nil {
		log.Fatalf("Failed to create driver: %v", err)
	}

	// Return the driver instance
	return &DatabaseDriver{Driver: driver}
}

// Close function to close the database driver
func (d *DatabaseDriver) Close(c context.Context) {
	if err := d.Driver.Close(c); err != nil {
		log.Printf("Failed to close Neo4j driver: %v", err)
	}
}

Bolt protocol⁶ is a lightweight, binary, and efficient protocol used for communication between Neo4j clients and servers. It supports streaming result and TLS based secure communication.

Step 4. Create node

This is the CQL to create a User node.

CREATE (u:User {name: $name}) RETURN u

• CREATE … define the action

• (u:User {name: $name}) … define the information of the node to create. u is alias of the user which was created (similar to AS keyword in SQL).

• RETURN u … define the value to return as the result

You can create the node via REST API endpoint POST /users. On the Neo4j browser, you see the result below.

Step 5. Create relationship

This is the CQL to create a relationship to connect 2 User nodes.

MATCH (a:User {name: $name1}), (b:User {name: $name2})
CREATE (a)-[:MARRY]->(b), (b)-[:MARRY]->(a)

• MATCH (a:User {name: $name1}), (b:User {name: $name2}) … find 2 User nodes which matches to the condition searched by the name attribute.

• CREATE … create 2 relationships below

  • (a)-[:MARRY]->(b) … create MARRY relationship from a to b

  • (b)-[:MARRY]->(a) ... create MARRY relationship from b to a

You can create the relationships via REST API endpoint POST /marriage. On the Neo4j browser, you see the result below.

Main References

• Neo4j

---

1. In some other graph databases, relationship is called edge.

2. Overview - Cypher Manual

3. neo4j - Official Image | Docker Hub

4. Neo4j Browser - Neo4j Browser

5. Gin Web Framework

6. Bolt Protocol documentation - Bolt Protocol