grex

Client for Rexster Graph Server

npm install grex
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Grex

Gremlin inspired Rexster Graph Server client for NodeJS and the browser.

Grex is a Gremlin generating library written in JavaScript which helps you build, send over HTTP and execute arbitrary strings of Gremlin against any Blueprint compliant Graph database.

If you're interested in an Object-to-Graph mapper library, you may also want to have a look at Mogwai.js.

Installation

Grex works both in Node.js or in the browser via Browserify.

$ npm install grex

You may also wish to use Grex in the browser, essentially when prototyping applications. Obviously Grex may not be used in production with graph database containing sensitive informations.

Quick start

Grex does 3 things: connect to a database, generate a Gremlin (Groovy flavored string) and send the string for execution (retrieving the results if any).

var settings = {
  'database': 'myGraphDB',
  'host': 'localhost',
  'port': 8182
};

// 1. connect() takes two optional parameters: a settings Object and a Node style callback
Grex.connect(settings, function(err, client) {
  if (err) {
    console.error(err);
  }

  // 2. Initialize a Gremlin object to work with
  var gremlin = client.gremlin();

  // Start appending some code
  gremlin.g.v(1); // gremlin.script === 'g.v(1)'

  // 3. Send script for execution, and return a response with the results (if any)
  gremlin.exec(function(err, response) {
    // ...
  })
});

Documentation

Two good resources to understand the Gremlin API are GremlinDocs and SQL2Gremlin.

Grex uses the Q module to return a Promise when calling the asynchronous exec() method.

Basic usage

Building a Gremlin script

The main object you'll be working with is an instance of Gremlin class.

var gremlin = Grex.gremlin() // Instantiate a new Gremlin script class.
gremlin.g.V('name', 'marko').out() // Appends strings
// gremlin.script == "g.V('name','marko').out"

Grex exposes Graph, Pipeline, Vertex and Edge wrapper classes with multiple methods which help you automatically generate a valid Gremlin string.

Each Gremlin instance is basically appending strings to an internal script variable as you issue more commands. Grex provides many high level method you should use when building your script (though experts are free to hack around and directly use the lower level Gremlin.line() or Gremlin.append() methods at their own risks).

Executing Gremlin script

A Gremlin script will be immediadly sent to Rexster for execution when you issue the .exec() command.

The previous example can thus be executed the following way:

gremlin.exec(function(err, response) {
  if(err) {
    console.error(err);
  }
  console.log(response);
});

Transactions

Multiple vertices and edges can be added in a transaction over one single http call.

var gremlin = client.gremlin();
var v1 = g.addVertex.addVertex({k1:'v1', 'k2':'v2', k3:'v3', id: 100}, 'vA');
var v2 = g.addVertex.addVertex({k1:'v1', 'k2':'v2', k3:'v3', id: 200}, 'vB');
g.addVertex.addEdge(v1, v2, 'pal' , { weight: '0.75f' });

gremlin.exec(function(err, response) {
  // Handle error or response
})

This will generate and send the following Gremlin script for execution to Rexster:

vA = g.addVertex(100, [k1: 'v1', k2: 'v2', k3: 'v3']);
vB = g.addVertex(200, [k1: 'v1', k2: 'v2', k3: 'v3']);
g.addEdge(vA, vB, 'pal', [weight: 0.75]);
// Note that Grex will actually automatically strip spaces away

Because JavaScript lacks reflection, you're required to supply an optional string identifier as the last parameter. This identifier will be used in the generated Gremlin string.

API differences between Gremlin Groovy and Grex JavaScript

For simplicity the callbacks are not included in the examples below. Gremlin generated strings are displayed first in the following examples.

Support for multiple arguments or Object argument

// Groovy
g.V('name', 'marko').out
// JavaScript
g.V('name', 'marko').out();
g.V({name: 'marko'}).out();

Support for multiple arguments or Array argument

// Groovy
g.v(1, 4).out('knows', 'created').in
// JavaScript
g.v(1, 4).out('knows', 'created').in();
g.v([1, 4]).out(['knows', 'created']).in();

Array indexes

// Groovy
g.V[0].name
// JavaScript
g.V().index(0).property('name');

Array ranges

// Groovy
g.V[0..<2].name
/// JavaScript
g.V().range('0..<2').property('name');

Comparison tokens

Comparison tokens are currently passed in as strings.

// Groovy
g.E.has('weight', T.gt, 0.5f).outV.transform{[it.id,it.age]}
// JavaScript
g.E().has('weight', 'T.gt', '0.5f').outV().transform('{[it.id,it.age]}');

Passing of pipelines

// Groovy
g.V.and(_().both("knows"), _().both("created"))
// JavaScript
g.V().and(gremlin._().both("knows"), gremlin._().both("created"))
// Groovy
g.v(1).outE.or(_().has('id', T.eq, "9"), _().has('weight', T.lt, 0.6f))
// JavaScript
g.v(1).outE().or(gremlin._().has('id', 'T.eq', 9), gremlin._().has('weight', 'T.lt', '0.6f'));
// Groovy
g.V.retain([g.v(1), g.v(2), g.v(3)])
// JavaScript
g.V().retain([gremlin.g.v(1), gremlin.g.v(2), gremlin.g.v(3)])

Closures

Closures are currently passed in as strings. See https://github.com/gulthor/grex/issues/22 for a discussion on using JavaScript functions.

// Groovy
g.V.out.groupBy{it.name}{it.in}{it.unique().findAll{i -> i.age > 30}.name}.cap
// JavaScript
g.V().out().groupBy('{it.name}{it.in}{it.unique().findAll{i -> i.age > 30}.name}').cap()

Java classes

Java classes are currently passed in either as strings or as JavaScript objects.

// Groovy
g.createIndex("my-index", Vertex.class)
// JavaScript
g.createIndex("my-index", "Vertex.class")

Retrieving indexed Elements

// Groovy
g.idx("my-index")[[name:"marko"]]
// JavaScript
g.idx("my-index", {name:"marko"});

Notable differences

Grex tries to implement Gremlin (Groovy flavored) syntax as closely as possible. However, there are some notable differences.

  • All method calls require brackets (), even if there are no arguments.
  • Closures currently need to passed in as a string argument to methods. This will likely change in the future (see issue#22).

      g.v(1).out().gather("{it.size()}");
    
      g.v(1).out().ifThenElse("{it.name=='josh'}{it.age}{it.name}");
    
  • Comparators and Float's are not native javascript Types so they currently need to be passed in as a string to Grex methods. Floats need to be suffixed with a 'f'. This will probably change in future versions of Grex.

      g.v(1).outE().has("weight", "T.gte", "0.5f").property("weight")
    
  • Certain methods cannot (yet) be easily implemented. Such as aggregate, store, table, tree and fill. These methods require a local object to populate with data, which cannot be easily done in this environment.
  • Tokens/Classes: You will notice that in the examples tokens are passed as string (i.e. 'T.gt'). However, Grex also exposes some objects for convenience to make it feel more natural. To access the objects, reference them like so:

      var T = Grex.T;
      var Contains = Grex.Contains;
      var Vertex = Grex.Vertex;
      var Edge = Grex.Edge;
    

You can now use these objects in place of the string representation in your queries.

API

Grex

Grex.connect(Object)

Options specify the location and name of the database.

  • host (default: localhost): Location of Rexster server
  • port (default: 8182): Rexster server port
  • graph (default: tinkergraph): Graph database name
  • idRegex (default: false): This can remain as false, if IDs are number. If IDs are not numbers (i.e. alpha-numeric or string), but still pass parseFloat() test, then idRegex must be set. This property will enable Grex to distinguish between an ID and a float expression.
Grex.connect({
  host: 'myDomain',
  graph: 'myOrientdb',
  idRegex: /^[0-9]+:[0-9]+$/
});

Gremlin

Gremlin.g

A getter property. Returns a new Graph() wrapper instance. See https://github.com/gulthor/grex/blob/master/src/gremlin.js.

Graph methods return convenient wrapper objects, which is either:

  • a new Pipeline instance (ie. by calling g.v(), g.V(), g.E(), etc.)
  • a new Vertex via g.addVertex() or new Edge instance via g.addEdge(). Both classes inherits from Element.

See: https://github.com/gulthor/grex/blob/master/src/graph.js.

Gremlin.exec(callback)

Sends the generated gremlin.script to the server for execution. This method either takes a callback, or returns a promise.

Gremlin.append(String)

Appends an arbitrary string to the gremlin.script. This method is used internally but can be useful on some occasions. Use with caution.

Gremlin.line(String)

Appends an arbitrary string to the gremlin.script preceded by a \n character. This method is used internally but can be useful on some occasions. Use with caution.

Todo

  • bound arguments (for better performance)
  • closure as JavaScript functions
  • simplified API (remove gremlin.g and gremlin._, remove Java .class, etc.)
  • Rexpro
  • performance checks and improvements

Author

Jean-Baptiste Musso - @jbmusso.

Based on the work by Frank Panetta - @entrendipity.

Contributors

https://github.com/gulthor/grex/graphs/contributors

License

MIT (c) 2013-2014 Entrendipity Pty Ltd, Jean-Baptiste Musso.

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