MongoHooks

A thin listener and before/after filter extension for the mongojs node-module.

Install

npm install mongohooks

Example

var db = require('mongojs')('mydb', ['members']); // load mongojs as normal
var mongohooks = require('mongohooks');
 
// Add a `createdAt` timestamp to all new documents
mongohooks(db.members).save(function (document, next) {
  document.createdAt = new Date();
  next();
});
 
// Now just use the reqular mongojs API
db.members.save({ name: "Thomas" }, function (error, result) {
  console.log("Created %s at %s", result.name, result.createdAt);
});

Usage

This module will add 3 kinds of hooks to mongojs, each allowing you to add Before filters, After filters, and Listeners to any MongoDB collection.

Before filters are injected as middleware and is called before the actual call to the MongoDB database. You can add more than one before filter to the same mongojs function, in which case they are called in order. Each filter have access to all the arguments passed to the original mongojs function.

A before filter can be used to manipulate for instance a document before it's saved or a query before it's executed.

After filters are also injected as middleware and is called after the mongojs function have finished but before the callback given to the mongojs function is called. After filters are useful for validating or manipulating returned documents.

As opposed to before filters, which are called only once per call to mongojs, after filters are called once per document in the result set.

Listeners act as simple async monitors. They are similar to after filters in that they are called after the MongoDB command have returned, but they do not interfere with the normal operation of the MongoDB query and are hence ideal for logging purposes or derived operations. Also, a listener have access to both the original arguments sent to mongojs and the returned error and result parsed to the callback.

Before filters

Hook into .save(), .insert(), .update(), .find(), and .findOne():

// Add a before filter to db.members.save
mongohooks(db.members).save(function (document, next) {...});
 
// Add a before filter to db.members.insert
mongohooks(db.members).insert(function (document, next) {...});
 
// Add a before filter to db.members.update
mongohooks(db.members).update(function (query, <update>, <options>, next) {...});
 
// Add a before filter to db.members.find and db.members.findOne
mongohooks(db.members).find(function (criteria, <projection>, next) {...});

Filters are async, so remember to call the next callback when you are done:

mongohooks(db.members).find(function (criteria, next) {
  // do stuff
  next();
});

Before filters can abort the execution by passing on an error:

mongohooks(db.members).find(function (criteria, next) {
  next(new Error());
});

Use the this keyword to access the collection

mongohooks(db.members).update(function (query, update, options, next) {
  // perform a find before each update
  this.findOne({ foo: 1 }, function (error, result) {
    // do stuff
    next();
  });
});

After filters

Allows you to monitor or modify documents returned by either .find() or .findOne().

The after filter is called once for each document in a returned result and have access to both the document and the optional projection used when the query was performed.

mongohooks(db.members).document(function (document, projection, next) {...});

Filters are async, so remember to call the next callback when you are done:

mongohooks(db.members).document(function (document, projection, next) {
  // do stuff
  next();
});

After filters can also parse on errors:

mongohooks(db.members).document(function (document, projection, next) {
  next(new Error());
});

Listeners

Mongohooks also acts as an event-emitter, notifying you after calls to either .save(), .insert() or .update().

Add listeners using the .on() function, which takes two arguments: The event to listen to (save, insert or update) and a callback function to call when the event is emitted. The format of the callback function is callback(error, result, <arg1>, <arg2>, <...>).

The first two arguments is always the error and result normally passed to the mongojs callback, followed by the arguments of the mongojs function that triggerd the event. E.g. if you listen for update events, expect 5 arguments in the callback: error, result, query, update, and options:

mongohooks(db.members).on('save', function (error, result, query, update, options) {
  // error   : null (unless something went wrong)
  // result  : { ... } (in case of the save command, this will be a lastErrorObject)
  // query   : { _id: "foo" }
  // update  : { name: "Anders" }
  // options : undefined (since no options object was passed to the update function)
});
 
// perform the update
db.members.update({ _id: "foo" }, { name: "Anders" });

Chaining

Filters can be chained and multiple filters of the same type can be added

mongohooks(db.members)
  .update(function (query, <update>, <options> next) {...})
  .find(function (criteria, <projection>, next) {...})
  .find(function (criteria, <projection>, next) {...})
  .document(function (document, projection, next) {...})
  .on('save', function (err, result, document) {...});

Todo

• Add support for .remove() hooks
• Add support for .findAndModify() hooks

Disclamer

This module was originally hacked together in a post-drunken state at a Copenhagen Node.js Hackathon event in just a few hours. Bugs might still exist.

License

MIT