How to call external function in background tasks in arangodb

Question

I have a functionality fully working and I want to call this every 30 min from background task. But It is not calling and throwing error as 'undefined'.

app.js

function hourly() { require("console"); console.log('I am running');}

controller.get('/testOnce', function(req, res) {
    var tasks = require("org/arangodb/tasks");

    tasks.register({
        id : "Test",
        name : "Testing background task",
        period : 5,
        command : "hourly()"
    });
});

I tried defining hourly in a separate js and then calling that with 'require' But this throws cannot locate module 'myjob'

myjob.js

function hourly() { require("console"); console.log('I am running');

app.js

controller.get('/testOnce', function(req, res) {
var tasks = require("org/arangodb/tasks");

tasks.register({
    id : "Test",
    name : "Testing background task",
    period : 5,
    command : "var job = require('myjob');"
});

});

Answer 1

The contents of the command attribute cannot refer to variables defined in other scopes. For example, in the app.js variant you're using a variable named hourly which may not be present anymore when the command gets executed.

In the simple case of just logging something, the app.js variant could be made working if its command parameter is changed to the following (which won't require any variables):

var tasks = require("org/arangodb/tasks");
tasks.register({
    period : 5,
    command : "require('console').log('I am running from inline command');"
});

The variant that defines the job function in a separate file (named myjob.js) can be made working by making the function available via an export of that module:

function hourly() { 
  require("console").log('I am running from myjob.js');
}

exports.hourly = hourly;

This is because a require() will only expose what the module exported. In the above case the module will expose a function named hourly, which can now be invoked from a background task as follows:

var tasks = require("org/arangodb/tasks");
tasks.register({
    period : 5,
    command : "require('myjob').hourly();"
});

Please note that in order for this to work, the file myjob.js needs to be located in the module search path. IIRC that is js/node by default. Also note that this directory already includes the bundled modules and may change on ArangoDB updates.

If the regular command is to be executed from within a Foxx route, then using Foxx queues might also be an option as they should allow putting the script with the job function inside the application directory. However, I have not tried this yet.

Answer 2

The "Foxx way" of solving this would be using the queue and a script-based job (introduced in 2.6).

I've covered this in the last Foxx webinar and am working on a blog post and cookbook recipe.

The problem with doing it this way is that Foxx jobs can not be periodic in 2.6. The feature is planned for 2.7 but with 2.6 only just having been released, you probably won't be able to use it any time soon.

Personally I would recommend using an external scheduler and invoking the Foxx script from there (via the foxx-manager CLI or the HTTP API).