Support async app loading

[ryedin]

This is needed for the cases where the app wants to go fetch metadata during the loopback startup phase. The main use case is to grab data from a remote source in order to use introspection to build the models.

[bajtos]

Please omit the boilerplate code to keep the example short.

Example:

myAsyncThing.run(function(metadata) {
  // Configure LoopBack models and datasources
  app.boot(__dirname);

  //use the model metadata to introspectively register new models
  myAsyncThing.buildModels(metadata);

  // other configuration as scaffolded by `slc lb project`
  app.use(loopback.favicon());
  // etc.
  app.enableAuth();

  //app API is ready to go -- time to alert anyone who cares (lookin' at you grunt-loopback-angular)
  doOnReady();

  if(require.main === module) {
    // start the http server
  }
});

[ryedin]

not a problem... update to PR coming

[bajtos]

Hi @ryedin, thank you for the pull request. The feature makes sense. See the comments above for things to improve/fix.

[slnode]

Can one of the admins verify this patch? To accept patch and trigger a build add comment ".ok\W+to\W+test."

[ryedin]

PR updated with recommended changes.

[bajtos]

Excellent, the patch looks much better now.

I was figuring what's being tested is "everything still works when the loopback app being introspected has been loaded asynchronously", so I thought it made sense to re-run all the tests.

Makes sense. IMO the extra complexity needed to implement this outweigh the benefits.

A side of effect of changing to an event rather than a callback registration function is that it became even harder to test in the context of using the grunt task in multi- mode.

I look to your guidance there... I personally don't think that's a huge issue because I can't imagine a real world case where you'd be running this task against multiple configuration options and outputting multiple outputs for a single app. The problem of course comes from the caching nature of require (once the task runs once, the app has been required and the specified ready event has long gone...)

Here are few possible solutions:

1. Ensure the app file is not cached. The drawback: the app boostrap is repeated for every configuration, which can add up to a long duration.

   delete require.cache[require.resolve(path.resolve(appFile))];
   app = require(path.resolve(appFile));

2. Keep track of which app objects were already initialised, e.g. by injecting a flag to the app object. Since the app object is thrown away later, it should be ok to modify it.

   if (options.appReadyEvent && !app.__isReady) {
     //register with the app's ready event
     app.on(options.appReadyEvent, function() {
       app.__isReady = true;
       completeTask();
     });  
   } else {
     completeTask();
   }

[bajtos]

test:sync and test:async are no longer needed, the async test can be defined in the same way as default_options and custom_options:

     loopback_angular: {
        options: {
          input: 'test/fixtures/app.js'
        },
        default_options: {
          options: {
            output: 'tmp/default_options'
          }
        },
        custom_options: {
          options: {
            output: 'tmp/custom_options',
            ngModuleName: 'customServices',
            apiUrl: 'http://custom/api/'
          }
        },
        async_app: {
          options: {
            input: 'test/fixtures/app-async.js',
            output: 'tmp/async_app'
          }
        }
      },

The nodeunit test code can go to test/loopback_angular_test.js.

Mayhap I am missing the point of separating sync & async tests. What benefits do you see in splitting sync and async tests?

[bajtos]

Hey @ryedin, what's the status of this pull request? Are you still keen to finish it up?

Note that loopback-boot now supports async booting process OOTB, see strongloop/loopback-boot#77 and strongloop/loopback-boot#50

[slnode]

Can one of the admins verify this patch? To accept patch and trigger a build add comment ".ok\W+to\W+test."

[bajtos]

This pull request seems to be abandoned, I am closing it. Feel free to reopen when you are ready to update and finish it.