Using deferrables to perform operations on Redis

[Patrick Mulder]

Hi!

I want to understand how to use the Deferrable module from JSClass.

The context where I am working is an action to create a User in a Redis hash:

1. Increase counter to get ID

2. Set Redis hash of user with ID

3. Return created user from Redis

I now have:

  var incrId = function() {

    var promise = new Promise();

    client.hincrby('users', 'count', 1, function(err, id){

      promise.succeed(addUser); 

    });

    return promise;

  };

  var addUser = function() {

     // never gets called

  };

  incrId();  // main call

Any ideas why the promise doesn't call addUser?

Thanks!

[Patrick Mulder]

Additionally Promise is defined with:

var Class = require('jsclass/src/core').Class;

var Deferrable = require('jsclass/src/deferrable').Deferrable;

var Promise = new Class({

  include: Deferrable,

  

  initialize: function(value) {

    // if value is already known, succeed immediately

    if (value !== undefined) this.succeed(value);

  }

});

[James Coglan]

On 11 October 2013 16:08, Patrick Mulder <mulder....@gmail.com> wrote:

The context where I am working is an action to create a User in a Redis hash:

1. Increase counter to get ID

2. Set Redis hash of user with ID

3. Return created user from Redis

I now have:

  var incrId = function() {

    var promise = new Promise();

    client.hincrby('users', 'count', 1, function(err, id){

      promise.succeed(addUser); 

    });

    return promise;

  };

  var addUser = function() {

     // never gets called

  };

  incrId();  // main call

Any ideas why the promise doesn't call addUser?

Deferrable#succeed takes a *value* and passes it to callbacks registered with callback() what you probably want is this:

  var incrId = function() {

    var promise = new Promise();

    client.hincrby('users', 'count', 1, function(err, id){

      promise.succeed(id); 

    });

    return promise;

  };

  var addUser = function(id) {

     // never gets called

  };

  incrId().callback(addUser);

However these days I wouldn't recommend using Deferrable, it's an old thing that predates the standardized Promise interface (http://promisesaplus.com/). Find an implementation of that (some npm modules: q, rsvp, promise) instead.

[Patrick Mulder]

On Saturday, October 12, 2013 2:42:55 PM UTC+2, James Coglan wrote:

However these days I wouldn't recommend using Deferrable, it's an old thing that predates the standardized Promise interface (http://promisesaplus.com/). Find an implementation of that (some npm modules: q, rsvp, promise) instead.

Thanks, it is definitively a jungle of npm modules out there addressing this.

I like bluebird as discussed here:

http://stackoverflow.com/questions/19321905/how-to-use-deferrable-to-execute-a-sequence-of-redis-operations/19327987#19327987