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default	I want to traverse a graph using a custom visitor from node

Using a custom visitor from node.js

Problem

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

Solution

Use arangojs{:target="_blank"} 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

bower install arangojs

Example data setup

For the following example, we need the example graph and data from here{:target="_blank"}. 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{:target="_blank"}

Tags: #graph #traversal #aql #nodejs

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