Support promises

[coodoo]

LoopBack should provide Promise-enabled API out of the box. The plan is to use the approach outlined in nodejs/node#173.

Tasks

• Support Promise-returning method and hooks strong-remoting#179 support promises in strong-remotin
• Promises for operation hooks loopbackio/loopback-datasource-juggler#449 loopback-datasource-juggler - support promises in "operation hooks"
• Promisify DAO loopbackio/loopback-datasource-juggler#451 and Related Models Promisification loopbackio/loopback-datasource-juggler#452 loopback-datasource-juggler - convert all DAO & relation methods to dual callback/promise API
• promisify juggler's DataSource methods like automigrate, autoupdate, discover*, etc.
  • Promisify 'automigrate' loopbackio/loopback-datasource-juggler#630
• promisify juggler's relation and scope methods
  • Promisify relation/scope methods in juggler #2709
• promisify custom validators in juggler
• WIP: Custom validator promises and options loopbackio/loopback-datasource-juggler#1229
• convert loopback builtin models to support dual callback/promise API
  • User - Promisify User model #1493
  • Application - Promisify 'Application' model #1533
  • PersistedModel (replication, change tracking) - Promisify 'PersistedModel - replication' #1536
  • Change
  • Checkpoint
  • Scope
  • Model.checkAccess()
  • AccessToken
  • Role (and role resolvers)
  • RoleMapping
  • ACL
• Promisify app.listen
• Modify connectors and convert all mixin methods to dual callback/promise API
  • loopback-connector-remote
  • Email model & connector
• (?) Allow middleware handlers to return a promise
• Support promises in loopback-phase, both for API and for handler functions
• Update examples and docs
  • Enhance strong-docs to support @promise annotation Support @promise annotation strong-docs#63
  • Edit API docs / Mark all functions supporting promises with @promise attribute
    • loopback-datasource-juggler
    • loopback-core
    • strong-remoting
    • loopback-connector-rest
  • Wiki docs with basic desc of new promise support (differences, etc) Concept / task docs for using LB Promise APIs #1575
  • Add / modify example apps using Promises Add or modify examples using Promises API #1576

---

Below is the original proposal from @coodoo.

I've been playing around with bluebird's promisifyAll() for a while, ended up I found it just take a couple of line to wrap the model and make it become async-compatible.

See code below:

var Promise = require("bluebird");

module.exports = function(ResetKey) {

// once a model is attached to the data source
ResetKey.on('dataSourceAttached', function( obj ){

    // wrap the whole model in Promise
   // but we need to avoid 'validate' method 
    ResetKey = Promise.promisifyAll( ResetKey, {filter: function(name, func, target){
      return !( name == 'validate');
    }} );
  })

}

Once the model is wrapped, we can use Promise syntax instead of callbacks:

// old way - callbacks
user.save(function(err, result){...})

// new way - promise
user.saveAsync()
.then(function(result){...})
.catch(function(err){...})

Ain't that lovely? :)

Of course it would be even better if all those happened higher up in the chain and become default.

Thought?

[wqli78]

+1

[glesage]

+1

[wpjunior]

+1

[offlinehacker]

+1
On Aug 3, 2014 12:41 PM, "Wilson Júnior" notifications@github.com wrote:

+1

—
Reply to this email directly or view it on GitHub
#418 (comment).

[nowherenearithaca]

This might be of interest to folks - talk on InfoQ about large nodejs project at kixeye where Paul Hill discusses why they liked Promises - http://www.infoq.com/presentations/kixeye-rest-api. While there is a ton of useful info in this talk, he specifically discusses Promises (they used Bluebird) starting at about 21:50. Besides the syntactic sugar/readability, he highlights how there is an "implicit try-catch" that allows centralizing error handling/logging. He also shows a code snippet (25:51) for how they did this that might be a useful pattern to consider including in the docs at some point, if possible.

[raymondfeng]

Thank you all for the input. We're building a list of roadmap items at https://github.com/strongloop/loopback/wiki/Roadmap-brainstorming. 'Promise' is on the list too. Maybe we should move it to a gist so that community ideas can be accepted via PRs.

[partap]

I've actually been using something similar...after boot(app), insert:

Promise   = require 'bluebird'
bbutil    = require 'bluebird/js/main/util'
for model, p of app.models
  Promise.promisifyAll p, filter: (name, func, target) ->
    return bbutil.isIdentifier(name) &&
      !bbutil.isClass(func) &&
      name.charAt(0) isnt '_' &&
      name.indexOf('Async') is -1 &&
      name isnt 'app'

...pardon my coffeescript :)

This will promisify all the app's models at once. I have a couple more items in my filter to exclude attributes we don't need to promisify, but it basically works the same.

The main problem is that you can't use the promises in a boot script or model init script, but I think @coodoo takes care of that with his solution above (thanks!). You can use @coodoo's method for complex models, and then use the app.models loop to take care of the rest (it's ok to run promisifyAll() twice on the same object with this filter.

The other problem I've found is that it doesn't work for the model relations. For example:

user.posts.createAsync(...)

will fail...I'm not sure how to go about promisifying those "virtual selectors"
I'm not sure how or where they are defined or attached...