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Using a custom visitor from node.js

Problem

I want to traverse a graph using a custom visitor from node.js.

Solution

Use arangojs and an AQL query with a custom visitor.

Installing arangojs

First thing is to install arangojs. This can be done using npm or bower:

npm install arangojs

or

bower install arangojs

Example data setup

For the following example, we need the example graph and data from here. Please download the code from the link and store it in the filesystem using a filename of world-graph-setup.js. Then start the ArangoShell and run the code from the file:

require("internal").load("/path/to/file/world-graph-setup.js");

The script will create the following two collections and load some data into them:

  • v: a collection with vertex documents
  • e: an edge collection containing the connections between vertices in v

Registering a custom visitor function

Let’s register a custom visitor function now. A custom visitor function is a JavaScript function that is executed every time the traversal processes a vertex in the graph.

To register a custom visitor function, we can execute the following commands in the ArangoShell:

var aqlfunctions = require("org/arangodb/aql/functions");

aqlfunctions.register("myfunctions::leafNodeVisitor", function (config, result, vertex, path, connected) {
  if (connected && connected.length === 0) {
    return vertex.name + " (" + vertex.type + ")";
  }
});

Invoking the custom visitor

The following code can be run in node.js to execute an AQL query that will make use of the custom visitor:

Database = require('arangojs'); 

/* connection the database, change as required */
db = new Database('http://127.0.0.1:8529'); 

/* the query string */
var query = "FOR result IN TRAVERSAL(v, e, @vertex, 'inbound', @options) RETURN result";

/* bind parameters */
var bindVars = { 
  vertex: "v/world",  /* our start vertex */
  options: {
    order: "preorder-expander",
    visitor: "myfunctions::leafNodeVisitor",
    visitorReturnsResults: true 
  }
};

db.query(query, bindVars, function (err, cursor) {
  if (err) {
    console.log('error: %j', err);
  } else {
    cursor.all(function(err2, list) {
      if (err) {
        console.log('error: %j', err2);
      } else {
        console.log("all document keys: %j", list);
      }
    });
  }
});

Author: Jan Steemann

Tags: #graph #traversal #aql #nodejs