This is an architectural question. I have models like this:

var foo = new mongoose.Schema({
  name: String,
  bars: [{type: ObjectId, ref: 'Bar'}]
});
var FooModel = mongoose.model('Foo', foo);

var bar = new mongoose.Schema({
  foobar: String
});
var BarModel = mongoose.model('Bar', bar);

Then I want to implement a convenience method like this:

BarModel.methods.addFoo = function(foo) {
  foo.bars = foo.bars || []; // Side note, is this something I should check here?
  foo.bars.push(this.id);

  // Here's the line I'm wondering about... Should I include the line below?
  foo.save();
}

The biggest con I see about this is that if I did include foo.save() then I should pass in a callback to addFoo so I avoid issues with the async operation. I'm thinking this is not preferable. But I also think it would be nice to include because addFoo hasn't really "addedFoo" until it's been saved... Am I breaking any design best practices doing it either way?