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...

[partap]

I was able to pause in the debugger and drill down a bit, but I'm still confused. There's some sort of convention for defining these methods that I'm not familiar with.

I'm looking at a user instance in the debugger...I'll try to asciify it :

user 
| ModelConstructor
|  __cachedRelations: Object
|  __dataSource: Object
| |__data: Object
| |  email: "joe@schmoe.com"
| |  id: ObjectId
| |  ...
| ...
| |__proto__: ModelConstructor
| |  __count__accessTokens: function (cb) {
| |  __create__accessTokens: function () {
| |  __delete__accessTokens: function () {
| |  ...

So if I understand this at all, it seems that anytime I access a property or method of a model instance, there's some javascript magic going on...user.id gets translated to user.__data.id, user.accessTokens.count() calls user.__count__accessTokens(), etc.

I saw similarly named methods in the lb-services.js file generated for angularjs...

...What is this magic and how does it work? :)

[raymondfeng]

The methods for relations are added to the model as properties with getters. For example, user.accessTokens will return a function bound to the user instance. The function itself also has other methods such as ‘create’, ‘count’, and ‘delete’. Please note the ____accessTokens methods are added to the User.prototype for legacy remoting purposes. These methods will probably be removed from the model prototype in the future.

Thanks,

---

Raymond Feng
Co-Founder and Architect @ StrongLoop, Inc.

StrongLoop http://strongloop.com/ makes it easy to develop APIs http://strongloop.com/mobile-application-development/loopback/ in Node, plus get DevOps capabilities http://strongloop.com/node-js-performance/strongops/ like monitoring, debugging and clustering.

On Nov 18, 2014, at 3:58 PM, Partap Davis notifications@github.com wrote:

I was able to pause in the debugger and drill down a bit, but I'm still confused. There's some sort of convention for defining these methods that I'm not familiar with.

I'm looking at a user instance in the debugger...I'll try to asciify it :

user
| ModelConstructor
| cachedRelations: Object
| __dataSource: Object
| |__data: Object
| | email: "joe@schmoe.com"
| | id: ObjectId
| | ...
| ...
| |__proto: ModelConstructor
| | __count__accessTokens: function (cb) {
| | __create__accessTokens: function () {
| | __delete__accessTokens: function () {
| | ...
So if I understand this at all, it seems that anytime I access a property or method of a model instance, there's some javascript magic going on...user.id gets translated to user.__data.id, user.accessTokens.count() calls user.__count__accessTokens(), etc.

I saw similarly named methods in the lb-services.js file generated for angularjs...

...What is this magic and how does it work? :)

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

[partap]

Hmm...ok, so if I understand correctly, all the properties and methods in models are defined using Object.defineProperty()?

1. I can kind of see the advantage in using this technique to define some properties, since you are transparently calling a function instead of just returning a value (eg: something like string.length, or anything that might require computation or might be cached or memoized). I'm curious, though, what is the advantage of that methodology for defining methods, as opposed to something like model.someMethod = someFunction.bind(model) or Model.prototype.someMethod = someFunction? It makes it hard to determine what the object's actual API is (although that might just be a limitation of the debugging tools?). I've been using javascript for years, but never found the need to use a getter. What magic goodness am I missing out on? :)
2. Where are the relations methods defined? I did a search for defineProperty and it seems to be used in the code a lot...
3. Is there a way to enumerate properties and methods defined using defineProperty()?
4. I'm wondering if I could figure out some way to promisify the relations methods at boot time. My idea is that, since there are different promise libraries available (I used to use Q, and now have transitioned to Bluebird), it might be a better idea to allow the user to use whatever promise library they want rather than make strongloop dependent on a single library... @coodoo's trick uses dataSourceAttached ... I see there is also an attached event. Are there new events added between the 2 events? Would it be possible to add an application-wide event in the boot sequence...something like app.model.on('modelDefined') that would pass in the model name and constructor function for every model defined at boot time. Obviously it couldn't be done in the general case because any time in the app's lifetime I can extend a model or define a new one, but it seems like it would be possible during boot, since everything is defined from static resources.
5. The model definition process seems pretty complicated and scattered throughout several modules. Would it be possible for a walkthrough of the major steps so one could trace it through the code? It seems that most models have a ton of mixins, and while many of these classes are documented, there doesn't seem to be any comprehensive explanation of what classes will end up in your finished model object and why (Model, PersistedModel, DataAccessObject, Validatable, etc...). For more complete documentation, it might be nice to make a note in the API documentation for each class just what it is used for. Why would I use it? Is it standalone? mixin for a Model? mixin for a DataSource? Subclass of something? Is it automatically included in every single model? Conversely, the docs for major developer-facing classes should list any builtin subclasses and mixins and what module in which they are defined. e.g.: loopback-datasource-juggler sounds like a behind-the-scenes type of module for backend connectivity, but looks like it actually defines a lot of core model behavior that I would have had no idea to look for there...

Hmm...sorry about so many tangential questions...I got started and couldn't stop, hehe. Maybe we should move this thread into the google group? ...although, tbh, I rather prefer the markdown support here on github.

[bajtos]

My idea is that, since there are different promise libraries available (I used to use Q, and now have transitioned to Bluebird), it might be a better idea to allow the user to use whatever promise library they want rather than make strongloop dependent on a single library...

+1

Note that Node v0.12/io.js 1.0 will ship a native implementation of Promises.

Thus a possible solution for LoopBack is to use the global Promise object in v0.12/1.0 and let the user supply whatever implementation he likes in Node v0.10 via global.Promise=require('bluebird');

I started to look into ways how to add promises to Node core API in nodejs/node#173. IMO it would be best to apply the same approach in loopback, as it involves only about 2-3 changed lines per function.

[faridnsh]

Adding on, what you guys have said, it'd also be nice if remote methods could return promises.

[slawo]

Actually adding promises to all loopback calls and all LoopBack Sdk Angular functions would help greatly unifying the API, at least on the callback front.

[BerkeleyTrue]

The loopback angular sdk already returns promises. It is built out on ngResource. For instance, User.logout().$promise.then();

It would be nice to get promises built in to the query syntax as well.

[ulion]

@partap so the promises for model relationship still not work by the bluebird plan?

[shlomiassaf]

+1.

Could you please post a behavior schema for the future implementation of promises.

Since they are a solid future feature for JS we will see a lot of frameworks going towards them.
An example is CO which is Promise based now.

I would like to start using them but I would like my changes to be future proof.
Will you guys implement a bluebird type schema? (e.g "Async" suffix?)
Will you support it on the same function name and return a promise if CB is not supplied?

How is it going to be?

Thanks.

[pandaiolo]

I have wrapped everything in bluebird -Async promises, If that can influence the roadmap :-)

[mrfelton]

This is awesome. Using the techniques here I've been able to use Bluebird promises for most of my loopback code. The only exception I have found so far is the model relation methods which was mentioned earlier in this thread. Just wondering if anyone has come up with a way to promisify the complete model, including the relationship methods?

[PaddyMann]

Promisifying custom validators in loopback-datasource-juggler is missing from the checklist.

I've submitted a PR here: loopbackio/loopback-datasource-juggler#1229

Hoping to get your input @bajtos on what's needed on the testing front.

[bajtos]

Promisifying custom validators in loopback-datasource-juggler is missing from the checklist.

Added to the checklist. Thank you for the pull request too!

[anodynos]

It would be great if we could add support for a Promise to be returned for each loopback-component-XXX loaded status + more.

This will allow us to decide whether to perform a task or not, or even disable parts of the API's functionality, wait before running tests etc.

See for example this workaround beginning of a nice and simple loopback <--> components contract for auto-migration snowyu/loopback-component-auto-migrate.js#4

In summary we need a (lightweight) contract so components can be looked up as app.components['superPlugin'], and provide some rudimentary lifecycle (then) hooks (eg loaded, stopped etc) and even have a custom exported object.

[bajtos]

@anodynos thank you for the comment. Your request makes sense to me, however it's rather off topic in this thread, which is focused on modifying existing APIs to support dual callback/promise. Could you please open a new issue to discuss component registration/discovery?

[anodynos]

Thanks @bajtos - I opened it here #3248

[the-freshlord]

I noticed that when using promises with instance methods of PersistedModel, I get this error:

{ error: syntax error at or near "WHERE"
    at Connection.parseE (/Users/Emanuel/Desktop/SilverLogic/picks-loopback/node_modules/pg/lib/connection.js:569:11)
    at Connection.parseMessage (/Users/Emanuel/Desktop/SilverLogic/picks-loopback/node_modules/pg/lib/connection.js:396:17)
    at Socket.<anonymous> (/Users/Emanuel/Desktop/SilverLogic/picks-loopback/node_modules/pg/lib/connection.js:132:22)
    at emitOne (events.js:96:13)
    at Socket.emit (events.js:188:7)
    at readableAddChunk (_stream_readable.js:176:18)
    at Socket.Readable.push (_stream_readable.js:134:10)
    at TCP.onread (net.js:548:20)
  name: 'error',
  length: 87,
  severity: 'ERROR',
  code: '42601',
  detail: undefined,
  hint: undefined,
  position: '28',
  internalPosition: undefined,
  internalQuery: undefined,
  where: undefined,
  schema: undefined,
  table: undefined,
  column: undefined,
  dataType: undefined,
  constraint: undefined,
  file: 'scan.l',
  line: '1081',
  routine: 'scanner_yyerror' }

So perhaps support for instance methods on PersistedModel doesn't exist yet. I tried this when calling updatingAttributes and save.

[beeman]

@eman6576 that should work just fine. Can you post a reproduction of it?

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This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[bajtos]

@kjdelisle @raymondfeng I think we may need to address this issue as part of our work on LoopBackNext. At least the parts in juggler (e.g. scope methods), because we are reusing juggler in LoopBackNext so far.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

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This issue has been closed due to continued inactivity. Thank you for your understanding. If you believe this to be in error, please contact one of the code owners, listed in the CODEOWNERS file at the top-level of this repository.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been closed due to continued inactivity. Thank you for your understanding. If you believe this to be in error, please contact one of the code owners, listed in the CODEOWNERS file at the top-level of this repository.