Neo4j: Running a graph database with Docker and the Cypher query language

Introduction

Compared with RDMS (Relational Database Management System), which takes data objects as the main part, the relationship between entities and entities in graph database plays a main role and is expressed as triples. Graph databases can provide many superior performances, especially when there are many interrelated data entities in the data.

Neo4j is one of the earliest graph database systems, and this article examines it.

Neo4j uses Cypher Query language and cypher-shell tool for query work, and accesses Neo4j database through common Web browser with built-in UI. Additionally, Neo4j supports REST APIs.

Neo4j has a paid version and a free community version with some limitations (no clustering, no online backup, only one user database, no scaling, etc.). In this article, we'll launch the Neo4j Community Edition using Docker, briefly introduce its query language through examples, and how to perform backup and restore.

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Running Neo4j with Docker

$ docker run --rm --name neo4j -p 7474:7474 -p 7687:7687 neo4j:latest
…
Directories in use:
home: /var/lib/neo4j
config: /var/lib/neo4j/conf
logs: /logs
plugins: /var/lib/neo4j/plugins
import: /var/lib/neo4j/import
data: /var/lib/neo4j/data
certificates: /var/lib/neo4j/certificates
run: /var/lib/neo4j/run
Starting Neo4j.
…
2020–07–27 10:11:30.394+0000 INFO Bolt enabled on 0.0.0.0:7687.
2020–07–27 10:11:31.640+0000 INFO Remote interface available at [http://localhost:7474/](http://localhost:7474/)
2020–07–27 10:11:31.640+0000 INFO Started

Check it out - open your browser, go to http://localhost:7474, and use the default login Username: neo4j, Password: neo4j 

administrator password

Set a new password: --env NEO4J_AUTH

$ docker run --rm --name neo4j --env NEO4J_AUTH=neo4j/pass -p 7474:7474 -p 7687:7687 neo4j:latest
Changed password for user ‘neo4j’.
…

cypher-shell

To work with the database, either through the REST API or a native tool — cypher-shell.

$ docker exec -ti neo4j cypher-shell -u neo4j -p pass
Connected to Neo4j 4.1.0 at neo4j://localhost:7687 as user neo4j.
Type :help for a list of available commands or :exit to exit the shell.
Note that Cypher queries must end with a semicolon.
neo4j@neo4j>

Neo4j configuration file

The main configuration file is located in $NEO4J_HOME/conf/neo4j.conf path, for example /var/lib/neo4j/conf/neo4j.conf

root@65d8061ac13e:/var/lib/neo4j# head /var/lib/neo4j/conf/neo4j.conf
\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*
Neo4j configuration
For more details and a complete list of settings, please see
\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*
The name of the default database
dbms.default_database=neo4j

Redefine any settings - mount the new configuration file to the /conf directory.

All settings of neo4j.conf can be found here .

To get the current configuration from the shell - use dbms.listConfig() to call:

neo4j@neo4j> CALL dbms.listConfig()
YIELD name, value
WHERE name STARTS WITH ‘dbms.default’
RETURN name, value
ORDER BY name
LIMIT 3;

+ — — — — — — — — — — — — — — — — — — — — — — — — -+
| name | value |
+ — — — — — — — — — — — — — — — — — — — — — — — — -+
| “dbms.default_advertised_address” | “localhost” |
| “dbms.default_database” | “neo4j” |
| “dbms.default_listen_address” | “0.0.0.0” |
+ — — — — — — — — — — — — — — — — — — — — — — — — -+
3 rows available after 216 ms, consumed after another 13 ms

cypher-shell and CQL

Next let's operate with actual data.

CREATE

Create a node

neo4j@neo4j> create (test);
0 rows available after 56 ms, consumed after another 0 ms
Added 1 nodes

DELETE

delete node

neo4j@neo4j> MATCH (test) DETACH DELETE test;
0 rows available after 32 ms, consumed after another 0 ms
Deleted 1 nodes

To delete all records from the database - use (n)

neo4j@neo4j> MATCH (n) detach delete n;

Labels

Create a node labeled label1 whose Properties contains two keys — key1 and key2

neo4j@neo4j> create (node1:label1 {key1: “value1”, key2: “value2”} );
0 rows available after 47 ms, consumed after another 0 ms
Added 1 nodes, Set 2 properties, Added 1 labels

result

neo4j@neo4j> MATCH (node1) RETURN node1;
+ — — — — — — — — — — — — — — — — — — — — — — +
| node1 |
+ — — — — — — — — — — — — — — — — — — — — — — +
| (:label1 {key1: “value1”, key2: “value2”}) |
+ — — — — — — — — — — — — — — — — — — — — — — +

or by using RETURN - get the node in the same query immediately after creation

neo4j@neo4j> CREATE (node2:label2 {key1: “value1”, key2: “value2”} ) RETURN node2;
+ — — — — — — — — — — — — — — — — — — — — — — +
| node2 |
+ — — — — — — — — — — — — — — — — — — — — — — +
| (:label2 {key1: “value1”, key2: “value2”}) |
+ — — — — — — — — — — — — — — — — — — — — — — +

Use MATCH(n) RETURN n to display all matching results in the browser

Relations

New relationships can be created between any new nodes or between already existing nodes.

Create a relation between new nodes - -[r:RelationName]->

neo4j@neo4j> create (node3:label3 {key1: “value1”, key2: “value2”}) -[r:RelationName]-> (node4:label4{key1: “value1”, key2: “value2”}) RETURN node3, node4;
+ — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — -+
| node3 | node4 |
+ — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — -+
| (:label3 {key1: “value1”, key2: “value2”}) | (:label4 {key1: “value1”, key2: “value2”}) |
+ — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — -+
1 row available after 88 ms, consumed after another 8 ms
Added 2 nodes, Created 1 relationships, Set 4 properties, Added 2 labels

Create relationships between existing nodes - use MATCH to match these nodes

neo4j@neo4j> MATCH (node3:label3), (node4:label4) CREATE (node3) -[r:RelationName2]-> (node4) RETURN node3, node4;
+ — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — -+
| node3 | node4 |
+ — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — -+
| (:label3 {key1: “value1”, key2: “value2”}) | (:label4 {key1: “value1”, key2: “value2”}) |
+ — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — -+
1 row available after 124 ms, consumed after another 9 ms
Created 1 relationships

Backup && Restore

Data is stored in $NEO4J_HOME/data, which is actually a symlink to /data. view catalog

root@65d8061ac13e:/var/lib/neo4j# ls -l /var/lib/neo4j/data
lrwxrwxrwx 1 root root 5 Jul 23 09:01 /var/lib/neo4j/data -> /data
root@65d8061ac13e:/var/lib/neo4j# ls -l /data/
total 12
drwxrwxrwx 4 neo4j neo4j 4096 Jul 27 11:19 databases
drwxr-xr-x 2 neo4j neo4j 4096 Jul 27 11:19 dbms
drwxrwxrwx 4 neo4j neo4j 4096 Jul 27 11:19 transactions

Database files are stored in the databases directory, where two default databases can be found - system and neo4j, which can be found via show databases

neo4j@neo4j> show databases;
+ — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — +
| name | address | role | requestedStatus | currentStatus | error | default |
+ — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — +
| “neo4j” | “localhost:7687” | “standalone” | “online” | “online” | “” | TRUE |
| “system” | “localhost:7687” | “standalone” | “online” | “online” | “” | FALSE |
+ — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — +

 The system database is used for the system itself, while nedo4j is the default user database.

Neo4j dump

Create a new directory for saving data

$ mkdir -p /tmp/neo4/{data,logs}

Restart Neo4j, mount these directories into

$ docker run --rm --name neo4j --env NEO4J_AUTH=neo4j/pass -p 7474:7474 -p 7687:7687 -v /tmp/neo4/data/:/data -v /tmp/neo4/logs/:/logs neo4j:latest
Changed password for user ‘neo4j’.
Directories in use:
home: /var/lib/neo4j
config: /var/lib/neo4j/conf
logs: /logs
plugins: /var/lib/neo4j/plugins
import: /var/lib/neo4j/import
data: /var/lib/neo4j/data
certificates: /var/lib/neo4j/certificates
run: /var/lib/neo4j/run
…

view data

$ ll /tmp/neo4/data/databases/
total 0
drwxr-xr-x 2 7474 7474 720 Jul 27 16:07 neo4j
-rw-r — r — 1 7474 7474 0 Jul 27 16:07 store_lock
drwxr-xr-x 3 7474 7474 740 Jul 27 16:07 system

connect, create new data

$ docker exec -ti neo4j cypher-shell -u neo4j -p pass
neo4j@neo4j> create (test:tobackup);
0 rows available after 131 ms, consumed after another 0 ms
Added 1 nodes

To create a database dump, you first need to stop the instance (because the community version does not have an online backup function), otherwise the following error will appear

root@771f04312148:/var/lib/neo4j# neo4j-admin dump --database=neo4j --to=/data/backups/
The database is in use. Stop database ‘neo4j’ and try again.

 therefore

$ docker stop neo4j

Restart it, but this time add the bash command to prevent the Neo4j service from starting

$ docker run -ti --rm --name neo4j --env NEO4J_AUTH=neo4j/pass -p 7474:7474 -p 7687:7687 -v /tmp/neo4/data/:/data -v /tmp/neo4/logs/:/logs neo4j:latest bash
neo4j@6d4e9854bc1d:~$

Create a dump

neo4j@015ba14bdba2:~$ mkdir /data/backup
neo4j@015ba14bdba2:~$ neo4j-admin dump --database=neo4j --to=/data/backup/
Done: 34 files, 250.8MiB processed.

Check

neo4j@015ba14bdba2:~$ ls -l /data/backup/
total 12
-rw-r — r — 1 neo4j neo4j 9971 Jul 27 13:46 neo4j.dump

recover

Create a new directory for the second Neo4j instance  

$ mkdir -p /tmp/neo4–2/{data,logs}

Copy the backup directory from the first directory

$ sudo cp -r /tmp/neo4/data/backup/ /tmp/neo4–2/data/

Run the service as usual, mount /tmp/neo4-2, replacing the port and its name

$ docker run — rm — name neo4j-2 — env NEO4J_AUTH=neo4j/pass -p 7475:7474 -p 7688:7687 -v /tmp/neo4–2/data/:/data -v /tmp/neo4–2/logs/:/logs neo4j:latest

Connect and check data

$ docker exec -ti neo4j-2 cypher-shell -u neo4j -p pass
Connected to Neo4j 4.1.0 at neo4j://localhost:7687 as user neo4j.
Type :help for a list of available commands or :exit to exit the shell.
Note that Cypher queries must end with a semicolon.
neo4j@neo4j> match (n) return n;
+ — -+
| n |
+ — -+
+ — -+

OK -- nothing here, because it's a brand new database.

To exit, stop it and use bash to run:

$ docker run -ti --rm --name neo4j-2 --env NEO4J_AUTH=neo4j/pass -p 7475:7474 -p 7688:7687 -v /tmp/neo4–2/data/:/data -v /tmp/neo4–2/logs/:/logs neo4j:latest bash

neo4j@b0f324cb7c9b:~$

Use the --force key to load the dump into the database, since the default neo4j database already exists:

neo4j@7bca892e9538:~$ neo4j-admin load --from=/data/backup/neo4j.dump --database=neo4j --force
Done: 34 files, 250.8MiB processed.

Exit, restart again in the normal way, start the Neo4j process

$ docker run -ti --rm --name neo4j-2 --env NEO4J_AUTH=neo4j/pass -p 7475:7474 -p 7688:7687 -v /tmp/neo4–2/data/:/data -v /tmp/neo4–2/logs/:/logs neo4j:latest

connect, check

neo4j@neo4j> match (n) return n;
+ — — — — — — -+
| n |
+ — — — — — — -+
| (:tobackup) |
+ — — — — — — -+

The data is in place - all done.