in-some-controller.js

var controller = this;

var success = function(model) {
  controller.transitionToRoute('...');
};

var failure = function(xhr) {
  controller.get('model').rollback();
  if (xhr.status == 400) {
    controller.showError($.parseJSON(xhr.responseText).detail);
  }
};

this.get('model').save().then(success, failure);