memgraph/docs/user_technical/quick-start.md

Quick Start

This chapter outlines several ways to execute openCypher queries on Memgraph, but first it's important to outline several technologies Memgraph uses.

OpenCypher

Memgraph supports the openCypher query language which has been developed by Neo4j. The language is currently going through a vendor-independent standardization process. It's a declarative language developed specifically for interaction with graph databases.

Bolt

Clients connect to Memgraph using the Bolt protocol. Bolt was designed for efficient communication with graph databases. Memgraph supports Version 1 of the protocol. Official Bolt protocol drivers are provided for multiple programming languages:

• Java
• Python
• JavaScript
• C#

It's also possible to interact with Memgraph using Neo4j's command-line tool, which is the easiest way for executing openCypher queries on Memgraph.

Graph Gists

A nice looking set of small graph examples could be found here. You can take any use-case and try to execute the queries against Memgraph. We welcome your feedback!

neo4j-client Example

The command-line neo4j-client can be installed as described on the official website.

The client can be started and connected to Memgraph with the following shell command:

neo4j-client bolt://<IP_ADDRESS>:<PORT> --insecure --user u --pass p

Where <IP_ADDRESS> and <PORT> should be replaced with the network location where Memgraph is reachable. The --insecure option specifies that SLL should be disabled (Memgraph alpha does not support SSL). --user and --pass parameter values are ignored by Memgraph (alpha is single-user), but need to be provided for the client to connect automatically.

After the client has started it should present a command prompt similar to:

neo4j-client 2.1.3
Enter `:help` for usage hints.
Connected to 'neo4j://neo@127.0.0.1:7687' (insecure)
neo4j>

At this point it is possible to execute openCypher queries on Memgraph. Each query needs to end with the ; (semicolon) character. For example:

CREATE (u:User {name: "Your Name"})-[:Likes]->(m:Software {name: "Memgraph"});

followed by:

MATCH (u:User)-[r]->(x) RETURN u, r, x;

Python Driver Example

Neo4j officially supports Python for interacting with an openCypher and Bolt compliant database. For details consult the official documentation and the GitHub project. Following is a basic usage example:

from neo4j.v1 import GraphDatabase, basic_auth

# Initialize and configure the driver.
#   * provide the correct URL where Memgraph is reachable;
#   * use an empty user name and password, and
#   * disable encryption (not supported).
driver = GraphDatabase.driver("bolt://localhost:7687",
                              auth=basic_auth("", ""),
                              encrypted=False)

# Start a session in which queries are executed.
session = driver.session()

# Execute openCypher queries.
# After each query, call either `consume()` or `data()`
session.run('CREATE (alice:Person {name: "Alice", age: 22})').consume()

# Get all the vertices from the database (potentially multiple rows).
vertices = session.run('MATCH (n) RETURN n').data()
# Assuming we started with an empty database, we should have Alice
# as the only row in the results.
only_row = vertices.pop()
alice = only_row["n"]

# Print out what we retrieved.
print("Found a vertex with labels '{}', name '{}' and age {}".format(
  alice['name'], alice.labels, alice['age'])

# Remove all the data from the database.
session.run('MATCH (n) DETACH DELETE n').consume()

# Close the session and the driver.
session.close()
driver.close()

Java Driver Example

The details about Java driver can be found on GitHub.

The example below is equivalent to Python example. Major difference is that Config object has to be created before the driver construction. Encryption has to be disabled by calling withoutEncryption method against the Config builder.

import org.neo4j.driver.v1.*;
import org.neo4j.driver.v1.types.*;
import static org.neo4j.driver.v1.Values.parameters;
import java.util.*;

public class JavaQuickStart {
    public static void main(String[] args) {
        // Initialize driver.
        Config config = Config.build().withoutEncryption().toConfig();
        Driver driver = GraphDatabase.driver("bolt://localhost:7687",
                                             AuthTokens.basic("",""),
                                             config);
        // Execute basic queries.
        try (Session session = driver.session()) {
            StatementResult rs1 = session.run("MATCH (n) DETACH DELETE n");
            StatementResult rs2 = session.run(
                "CREATE (alice: Person {name: 'Alice', age: 22})");
            StatementResult rs3 = session.run( "MATCH (n) RETURN n");
            List<Record> records = rs3.list();
            Record record = records.get(0);
            Node node = record.get("n").asNode();
            System.out.println(node.get("name").asString());
        } catch (Exception e) {
            System.out.println(e);
            System.exit(1);
        }
        // Cleanup.
        driver.close();
    }
}

Javascript Driver Example

The details about Javascript driver can be found on GitHub.

The Javascript example below is equivalent to Python and Java examples. SSL can be disabled by passing {encrypted: 'ENCRYPTION_OFF'} during the driver construction.

Here is an example related to Node.js. Memgraph doesn't have integrated support for Web Socket which is required during the execution in any web browser. If you want to run openCypher queries from a web browser, websockify has to be up and running. Requests from web browsers are wrapped into Web Socket messages, and a proxy is needed to handle the overhead. The proxy has to be configured to point out to Memgraph's Bolt port and web browser driver has to send requests to the proxy port.

var neo4j = require('neo4j-driver').v1;
var driver = neo4j.driver("bolt://localhost:7687",
                          neo4j.auth.basic("neo4j", "1234"),
                          {encrypted: 'ENCRYPTION_OFF'});
var session = driver.session();

function die() {
  session.close();
  driver.close();
}

function run_query(query, callback) {
  var run = session.run(query, {});
  run.then(callback).catch(function (error) {
    console.log(error);
    die();
  });
}

run_query("MATCH (n) DETACH DELETE n", function (result) {
  console.log("Database cleared.");
  run_query("CREATE (alice: Person {name: 'Alice', age: 22})", function (result) {
    console.log("Record created.");
    run_query("MATCH (n) RETURN n", function (result) {
      console.log("Record matched.");
      var alice = result.records[0].get("n");
      console.log(alice.labels[0]);
      console.log(alice.properties["name"]);
      session.close();
      driver.close();
    });
  });
});

Limitations

Memgraph is currently in alpha stage, and has a number of limitations we plan to remove in future versions.

Single query length

The maximum length of a query that can be sent from a driver in Python is 16378 characters, from a driver in Java 8184 and from a driver in JavaScript 1392 characters.

Multiple-Query Transactions

Even though Memgraph is a transactional database engine, transactions containing multiple queries are not yet supported. In other words, explicit transaction start and stop aren't yet supported. A transaction is created and committed implicitly for each executed query. If query execution fails, the transaction is aborted.

Multiple Users & Authorization

Memgraph is currently single-user only. There is no way to control user privileges. The default user has read and write privileges over the whole database.

Multiple Databases

Currently, a single Memgraph process exposes only one database that is implicitly used. To use multiple databases, it is necessary to launch multiple Memgraph processes.

Secure Sockets Layer (SSL)

Secure connections are not supported in alpha. For this reason each client driver needs to be configured not to use encryption. Consult driver-specific guides for details.

Node and edge IDs

Unique node and edge IDs are returned by the Bolt protocol to the client. In Memgraph these IDs are not guaranteed to be persistent during the whole database lifetime. They should never be used for any client side logic outside a single query/transaction scope.