Working with LoopBack objects

Overview

The primary LoopBack JavaScript objects are:

• App object
• Models
• Data sources

How to get a reference to these objects depends on where the code is (in a boot script, in a model JavaScript file /common/models/model.js, and so on) as well as which object you want to reference.

Getting the app object

Getting a reference to the app object is crucial, since from it you can obtain references to other objects such as models and data sources. You’ll typically want to get a handle on the app object in:

• Model scripts: /common/models/_modelName_.js (where modelName is the name of the model).
• Boot scripts in /server/boot

• Middleware (the ones you register in boot scripts and the ones in /server/server.js)

• Your own custom scripts

The app object provides context into various parts of a typical LB app.

From a boot script 

To get a reference to the app object in a boot script, pass it as the first parameter in the exported function.

Asynchronous boot script with a callback function:

module.exports = function(app, cb) { //app is injected by LoopBack
  //...
};

Synchronous boot script without a callback function:

module.exports = function(app) { //app is injected by loopback
  //...
};

As you can see from both examples, LoopBack provides the app object automatically as the first parameter in your boot scripts.

See Defining boot scripts for more information about boot scripts.

From middleware

LoopBack sets app object automatically in the request object in middleware (actually, under the hood, Express does it). You can access in server/server.js as follows:

...
app.use(function(req, res, next) {
  var app = req.app;
  //...
});
...

See Defining middleware for more information on middleware.

From a custom script

If you need a reference to app in your own custom scripts, simply require it (as in the models example):

var app = require('/server/server');
...

You simply require /server/server.js as you would any Node module.

From a model script

To get a handle on the app object in a model scaffolded by the Model generator, “require” it as you would any Node module:

var app = require('../../server/server'); //require `server.js` as in any node.js app

module.exports = function(Book) {
  //...
};

...
Book.app
...

module.exports = function(Book) {
  Book.app... //won't work because `.app` has not been added to the Book object yet
});

module.exports = function(Book) {
  Book.read(cb) {
    var app = Book.app;
    console.log(app.models...)
    cb();
  };
  Book.remoteMethod(
    'read',
    ...
  });
};

module.exports = function(MyModel) {
  var app;
  MyModel.on('attached', function(a) {
    app = a;
    // perform any setup that requires the app object
  });
};

var loopback = require('loopback');
var app = loopback();

module.exports = function(app) {
  var app = app.models.Book;
  //...
};

var app = require('/server/server');

require('../../server/server')

module.exports = function(MyModel) {
  var app = require('../../server/server');

  MyModel.observe('loaded', function( ctx, next) {
   var User = app.models.User;
   ...
   User.create(...);
   ...
});

module.exports = function(app) {
  var dataSource = app.datasources.db; //db can be any registered datasource in `/server/datasources.json`
  ...
};

var app = require('./server/server');
...
var datasource = app.datasources.db;
...

...
app.use(function(req, res, next) {
  var dataSource = app.datasources.db;
  ...
});
...

module.exports = function(Book) {
  Book.read = function() {
    var dataSource = Book.app.datasources.db;
  };
  Book.remoteMethod(
    'read',
     ...
  );
};

module.exports = function(Book) {
  Book.app... //`Book` is not registered yet! This WON'T WORK.
};