nosql

NoSQL

Neo4j console

Neo4j provides an online REPL (read--evaluate--print loop) console at http://console.neo4j.org/ to experiment with Cypher. A preloaded graph database is available at http://console.neo4j.org/r/39s1je.

• Delete root node if necessary.

  START n=node(0) 
  DELETE n
  

• Get all subjects.

  START n=node(*) 
  RETURN n
  

• Subjects with at least 4 credits that have an exam.

  START n=node(*) 
  WHERE n.credits >= 4 AND n.exam = true 
  RETURN n
  

• Subjects that are required to complete before some other subject.

  START n=node(*) 
  MATCH n-[r:ALAIRASRA_EPUL]->() 
  WHERE n.credits >= 4 AND n.exam = true 
  RETURN DISTINCT n
  

  Warning: don't forget the colon.

• Subjects that are not required to complete before any other subject.

  START n=node(*) 
  MATCH n-[r?:ALAIRASRA_EPUL]->() 
  WHERE n.credits >= 4 AND n.exam = true AND r IS NULL 
  RETURN DISTINCT n, r
  

• Subjects that are required to complete before an other subject, which can be taken simultaneously with some a third one.

  START n=nodes*) 
  MATCH n-[r:ALAIRASRA_EPUL]->m-[s:EGYUTT_VEHETO_FEL]s>o 
  RETURN n, r, m, s, o
  

• The query is equivalent to:

  START n=node(*) 
  MATCH n-[r:ALAIRASRA_EPUL]->m, m-[s:EGYUTT_VEHETO_FEL]->o 
  RETURN n, r, m, s, o
  

Embedded mode

Create a new Maven Project in Eclipse. Select Simple project (no archetype).

• Group Id: etr.neo4j
• Artifact Id: etr.neo4j.embedded

Dependencies

Go to Neo4j's homepage (http://www.neo4j.org/) and naviagte to Download | Maven dependency. Add the following dependency to the pom.xml with the version set to 1.8.2.

<dependency>
 <groupId>org.neo4j</groupId>
 <artifactId>neo4j</artifactId>
 <version>1.8.2</version>
</dependency>

Java code

Tips:

• Preferences | Java | Editor | Typing | Automatically insert at correct position | Semicolons.
• Use Extract to local variable refactor.

Create two classes in a package called embedded.

The Main class:

package embedded;

public class Main {
	public static void main(String[] args) {
		Neo4jHandler neo4jHandler = new Neo4jHandler();
		neo4jHandler.run();
	}
}

The Neo4jHandler class:

package embedded;

import java.io.File;
import java.io.IOException;
import java.util.Map;

import org.neo4j.cypher.javacompat.ExecutionEngine;
import org.neo4j.cypher.javacompat.ExecutionResult;
import org.neo4j.graphdb.GraphDatabaseService;
import org.neo4j.graphdb.Node;
import org.neo4j.graphdb.RelationshipType;
import org.neo4j.graphdb.Transaction;
import org.neo4j.graphdb.factory.GraphDatabaseFactory;
import org.neo4j.graphdb.index.Index;
import org.neo4j.graphdb.index.IndexManager;
import org.neo4j.kernel.impl.util.FileUtils;

public class Neo4jHandler {

	public void run() {
		String path = "neo4j-db";

		File file = new File(path);
		if (file.exists()) {
			try {
				FileUtils.deleteRecursively(file);
			} catch (IOException e) {
				e.printStackTrace();
			}
		}

		GraphDatabaseService graphDb = new GraphDatabaseFactory()
				.newEmbeddedDatabase(path);
		IndexManager index = graphDb.index();
		Index<Node> index_names = index.forNodes("__names__");

		Transaction tx = graphDb.beginTx();
		try {
			Node fiz1 = graphDb.createNode();
			fiz1.setProperty("name", "Fizika 1.");
			fiz1.setProperty("credits", 4);
			index_names.add(fiz1, "name", "Fizika 1.");

			Node fiz2 = graphDb.createNode();
			fiz2.setProperty("name", "Fizika 2.");
			fiz2.setProperty("credits", 4);
			index_names.add(fiz2, "name", "Fizika 2.");

			fiz1.createRelationshipTo(fiz2, EtrRelationship.VIZSGARA_EPUL);

			tx.success();
		} finally {
			tx.finish();
		}
	}

	enum EtrRelationship implements RelationshipType {
		VIZSGARA_EPUL, KREDITRE_EPUL, EGYUTT_VEHETO_FEL
	}

}

Neoclipse

Run Neoclipse (https://github.com/neo4j/neoclipse), create a new database connection to the neo4j-db directory. To test the application, run the following Cypher query in Neoclipse:

START n=node:__names__(name='Fizika 1.')
RETURN n.name, n.credits

Cypher query from Java

Add the Cypher query to the Java code. Warning: use the javacompat execution engine/result.

		ExecutionEngine engine = new ExecutionEngine(graphDb);
		String query = "START n=node:__names__(name='Fizika 1.')\r\n"
				+ "RETURN n.name, n.credits";
		ExecutionResult result = engine.execute(query);
		
		for (Map<String, Object> row : result) {
			System.out.println(row);
		}

Tip for inserting Cypher queries to Java: go to Preferences | Java | Editor | Typing and tick Escape text when pasting into a string literal.

To create the whole database, run the Cypher query from https://svn.inf.mit.bme.hu/edu/trunk/mdsd/handout/public/nosql_materials/elotanulmanyi_rend_cypher_ekezetes.txt

Eclipse will prompt to change the encoding of the file: choose UTF-8.

Tip: autocomment with Ctrl + 7 or Ctrl + Shift + C.

Server mode

Run the server with C:\neo4j-community-1.8.2\bin\Neo4j.bat.

If you get the error Unable to access jarfile C:\NEO4J-~1.2\bin\windows-service-wrapper-*.jar, you ran into the issue mentioned at https://github.com/neo4j/neo4j/issues/391. To solve it, edit base.bat: change

set wrapperJarFilename=windows-service-wrapper-*.jar

to

set wrapperJarFilename=windows-service-wrapper-4.jar

Using the REST API manually

Use the Advanced Rest Client to access the Neo4j server.

• URL: http://localhost:7474/db/data/cypher
• HTTP Method: POST
• Headers: Accept: application/json

The payload to the creation query is in the https://svn.inf.mit.bme.hu/edu/trunk/mdsd/handout/public/nosql_materials/rest_create_query.txt file.

Query all nodes with:

{
  "query" : "START n=node(*) RETURN n",
  "params" : {
  }
}

Observe how verbose the output is. Try the following query:

{
  "query" : "START n=node(*) RETURN n.name, n.credits",
  "params" : {
  }
}

Warning: this is not going to work if the root node still exists. Delete it with:

{
  "query": "START n=node(0) DELETE n",
  "params": {}
}

Run the previous Cypher query and observe how compact it's output is.

Web administration interface

You can access the web administration interface: http://localhost:7474/webadmin/. Observe the dashboard and play with the data browser.

REST API in Java

Create a Maven project in Eclipse.

• Group Id: etr.neo4j
• Artifact Id: etr.neo4j.embedded

Luckily, we have a great wrapper to use (https://github.com/neo4j/java-rest-binding), but it is not available in the Maven Central Repository.

Installing Maven

To install Maven, download from it http://maven.apache.org/download.cgi and follow the Installation Instructions.

In Windows, go to the System window (Windows + Break), click Advanced system settings | Environment variables... | System variables. Set the following variables:

• M2_HOME = c:\apache-maven-3.0.5
• M2 = %M2_HOME%\bin
• Path = <previous value of Path>;%M2%

Use mvn --version to test if it works.

In Debian-based Linux distributions, simply install with:

sudo apt-get install maven

Note that the maven package contains Maven 3 and the maven2 package contains Maven 2. You need the former.

Compiling the Neo4j java-rest-binding project with Maven

Retrieve the java-rest-binding project for Neo4j 1.8.

• The simple way: download https://svn.inf.mit.bme.hu/edu/trunk/mdsd/handout/public/nosql_materials/java-rest-binding-1.8.1.zip and unzip.

• The more adventurous way: clone the repository from GitHub:

  git clone git://github.com/neo4j/java-rest-binding.git
  

  Open a command line, navigate to the java-rest-binding directory. Switch to the 1.8.1 branch (note that the semantics of the git checkout command are different of the svn checkout command).

  git checkout 1.8.1 
  

Compile and install the project with the following command:

mvn clean install

If this fails, you may try the following:

mvn clean install -DskipTests

Use the dependency provided in the GitHub project's README.md file, but correct the version number to 1.8.2:

<dependency>
    <groupId>org.neo4j</groupId>
    <artifactId>neo4j-rest-graphdb</artifactId>
    <version>1.8.2</version>
</dependency>

Creating the Java application

Create a package called client and create the following classes:

The Main class:

package client;

public class Main {

	public static void main(String[] args) {
		Neo4jClient neo4jClient = new Neo4jClient();
		neo4jClient.run();
	}
	
}

The Neo4jClient class:

package client;

import java.util.Collection;
import java.util.Map;

import org.neo4j.helpers.collection.IteratorUtil;
import org.neo4j.helpers.collection.MapUtil;
import org.neo4j.rest.graphdb.RestAPI;
import org.neo4j.rest.graphdb.RestAPIFacade;
import org.neo4j.rest.graphdb.query.RestCypherQueryEngine;
import org.neo4j.rest.graphdb.util.QueryResult;

public class Neo4jClient {

	String serverUrl = "http://localhost:7474/db/data";
	RestAPI restApi = new RestAPIFacade(serverUrl);
	
	public void run() {
		RestCypherQueryEngine queryEngine = new RestCypherQueryEngine(restApi);
		String query = "START n=node(*) RETURN n.name AS name, n.credits AS credits";
		QueryResult<Map<String, Object>> queryResult = queryEngine.query(query, MapUtil.map());
		Collection<Map<String, Object>> result = IteratorUtil.asCollection(queryResult);
		
		for (Map<String, Object> map : result) {
			String name = (String) map.get("name");
			Integer credits = (Integer) map.get("credits");
			System.out.println(String.format(
					"%s (%d credits)", name, credits));
		}
		
		restApi.close();
	}

}

This will run the Cypher query through the REST API, and list the names and credit numbers of the subjects.