Mongraph [mɔ̃ ˈɡrɑːf]

Mongraph combines documentstorage database with graph-database relationships by creating a corresponding node for each document.

Mongraph is experimental

It's working with Neo4j v2.0.x - v2.1.x and MongoDB v2.x - v3.0

Installation

  $ npm install mongraph

or clone the repository to your project and install dependencies with npm:

  $ git clone git@github.com:pstaender/mongraph.git
  $ cd mongraph && npm install

What is it good for?

MongoDB is great for a lot of things but a bit weak at relationships. However Neo4j is very powerful at this point but not the best solution for document storage. So why not using the best of both worlds?

What does it take?

Every document which is created in MongoDB will have a corresponding node in Neo4j:

             [{ _id: 5169…2, _node_id: 1 }]                  -> document in MongoDB
                           / \
                            |
                            |
                           \ /
  ({ id: 1, data: { _id: 5169…2, _collection: 'people'} })   -> node in Neo4j

Each document has an extra attribute:

_node_id (id of the corresponding node)

Each node has extra attributes:

_id (id of the corresponding document)
_collection (name of the collection of the corresponding document)

Each relationship will store informations about the start- and end-point-document and it's collection:

  (node#a) - { _from: "people:516…2", _to: "locations:516…3" … } - (node#b)

What can it do?

To access the corresponding node:

  // We can work with relationship after the document is stored in MongoDB
  document = new Document({ title: 'Document Title'});
  document.save(function(err, savedDocument){
    savedDocument.log(savedDocument._node_id); // prints the id of the corresponding node
    savedDocument.getNode(function(err, correspondingNode){
      console.log(correspondingNode); // prints the node
    });
  });

To access the corresponding document:

  console.log(node.data._id); // prints the id of the corresponding document
  console.log(node.data._collection); // prints the collection name of the corresponding 
  node.getDocument(function(err, correspondingDocument){
    console.log(correspondingDocument); // prints the document
  });

You can create relationships between documents like you can do in Neo4j with nodes:

  // create an outgoing relationship to another document
  // please remember that we have to work here always with callbacks...
  // that's why we are having the streamline placeholder here `_` (better to read)
  document.createRelationshipTo(
    otherDocument, 'similar', { category: 'article' }, _
  );
  // create an incoming relationship from another document
  document.createRelationshipFrom(
    otherDocument, 'similar', { category: 'article' }, _
  );
  // create a relationship between documents (bidirectional)
  document.createRelationshipBetween(
    otherDocument, 'similar', { category: 'article'},  _
  );

You can get and remove relationships from documents like you can do in Neo4j:

  // get all documents which are pointing via 'view'
  document.incomingRelationships('view', _);
  // get all documents that are connected with 'view' (bidirectional)
  document.allRelationships('view', _);
  // same between documents
  document.allRelationshipsBetween(otherDocument, 'view', _);
  document.incomingRelationshipsFrom(otherDocument, 'view', _);
  document.outgoingRelationshipsTo(otherDocument, 'view', _);

You can filter the documents (mongodb) and the relationships (neo4j):

  // get all similar documents where title starts with an uppercase
  // and that are connected with the attribute `scientific report`
  document.incomingRelationships(
    'similar',
    {
      where: {
        document: {
          // we can query with the familiar mongodb query
          title: /^[A-Z]/
        },
        // queries on graph are strings, because they are passed trough the cypher query directly for now
        // here: relationship objects are accessible as `r` by default, start node as `a` and end node (if is queried) as `b` 
        relationship: "r.category! = 'scientific report'"
      }
    }, _
  );

You can also make your custom graph queries:

  document.queryGraph(
    "START a = node(1), b = node(2) MATCH path = shortestPath( a-[*..5]->b ) RETURN path;", 
    { processPart: 'path' },
    function(err, path, options) { … }
  );

To get more informations about made queries (and finally used options) inspect the passed through options argument (debug: true enables logging of queries):

  document.incomingRelationships(
    'similar', { debug: true }, function(err, found, options) {
      // prints out finally used options and - if set to `true` - additional debug informations
      console.log(options.debug);
      // { cypher: [ "START … MATCH …" , …] … }}
    }
  );

Store in mongodb and neo4j simultaneously

Since v0.1.15 you can store defined properties from mongodb documents in the corresponding nodes in neo4j. It might be a matter of opinion whether it's a good idea to store data redundant in two database system, anyway mongraph provides a tool to automate this process.

You need to provide the requested fields in your mongoose schemas with a graph = true option. Please note: If the property includes the index = true option (used in mongoose to index property in mongodb) this field will be also indexed in the graphdatabase.

Since neo4j nodes store only non nested objects, your object will be flatten; e.g.:

  data = {
    property: {
      subproperty: true
    }
  };
  // will become
  // data['property.subproperty'] = true

messageSchema = new mongoose.Schema({
  text: {
    title: {
      type: String,
      graph: true // field / value will be stored in neo4j
      index: true, // will be an indexed in neo4j as well
    },
    content: String
  },
  from: {
    type: String,
    graph: true  // field / value will be stored in neo4j, but not be indexed
  }
});

Your documents + nodes on neo4j

By default all corresponding nodes are created indexed with the collection-name and the _id, so that you can easily access them through neo4j, e.g.:

  http://localhost:7474/db/data/index/node/people/_id/5178fc1f6955993a25004711

Requirements

Databases:

MongoDB (>2)
Neo4j (>2 and <2.2)

NPM modules:

mongoose ORM https://github.com/learnboost/mongoose npm install mongoose
Neo4j REST API client by thingdom https://github.com/thingdom/node-neo4j npm install neo4j

Changelogs

0.1.14

API Change: the collection of the corresponding document will be stored from now on as _collection instead of collection in each node. e.g.: node -> { data: { _id: 5ef6…, _collection: 'people' } }, reason: continious name conventions in node-, document-, relationship- + path objects

0.2.0

removed legacy node modules (source mapping for instance)
ignoring neo4j v<2
tested sucessfully against mongodb 2.6.x and Neo4J v2.0.x and v2.1.x

Testing

Not ready for Neo4j v2.2 since the neo4j module for the latest Neo4j version is still under development.

Older Neo4j version than 2.x are not supported anymore.

To run tests:

  $ mocha

Or specify a port for neo4j (default is set to 7474):

  $ mocha --globals=7010

This will run the tests against neo4j db on port 7010 - globals is a mocha specific argument which is used abusively as a workaround here ;)

License

See License file.

Contributors

Known issues and upcoming features

process tools should avoid loading all documents on specific mongodb queries -> more effective queries
using document _id as primary key in neo4j as well (in other words, drop support for node_id / id)
using labels-feature for nodes (neo4j 2.0+) instead of _collection property
dump and restore of relationships
real-life benchmarks