Support change-stream and liveset

[bajtos]

It would be nice to extend the generator to emit a different implementation of PersistedModel.createChangeStream(), so that the method returns a LiveSet instance.

See strongloop/loopback-example-angular-live-set#4

[EmileSpecs]

It is a little confusing however that this is in the generated User service:

/**
         * @ngdoc method
         * @name lbServices.User#createChangeStream
         * @methodOf lbServices.User
         *
         * @description
         *
         * Create a change stream.
         *
         * @param {Object=} parameters Request parameters.
         *
         *   This method does not accept any parameters.
         *   Supply an empty object or omit this argument altogether.
         *
         * @param {Object} postData Request data.
         *
         *  - `options` – `{object=}` - 
         *
         * @param {function(Object,Object)=} successCb
         *   Success callback with two arguments: `value`, `responseHeaders`.
         *
         * @param {function(Object)=} errorCb Error callback with one argument:
         *   `httpResponse`.
         *
         * @returns {Object} An empty reference that will be
         *   populated with the actual data once the response is returned
         *   from the server.
         *
         * Data properties:
         *
         *  - `changes` – `{ReadableStream=}` - 
         */
        "createChangeStream": {
          url: urlBase + "/Users/change-stream",
          method: "POST"
        }

It's because this simply seems to make a POST call to the change-stream endpoint and doesn't return any actual "change stream".

At it's simplest one would simply expect something like:

function changeStream(results) {
   var src = new EventSource(urlBase +'/Users/change-stream?access_token='+ LoopBackAuth.accessTokenId);
   var changes = createChangeStream(src); // you'll have to include the createChangeStream service
   if (results) return new LiveSet(results, changes); // you'll have to include the LiveSet service
   return changes;
}

Which would return the change stream that one could either listen for changes on:

var changes = changeStream();
changes.on('data', function(event) {
   console.log('new change event', event.target, event.data);
});

Or use it to create a LiveSet:

var liveSet = changeStream(results);

Might be over simplifying it a bit but essentially that would be it right?

[bajtos]

I'd say that ideally yes, your proposal is what it would be. Possibly with a small change - we may need to change createChangeStream to a promise that is eventually resolved as the stream object.

[mprokopowicz]

Any forecast for this one?

[cmvee]

Pulsing on this one - any thoughts on when createChangeStream might become functional?

[bajtos]

I am afraid this is not a priority for us. Having said that, if there are any volunteers willing to contribute this feature, then we are happy to help you along the way.