承诺

英文原文：http://emberjs.com/guides/models/persisting-records/

Ember Data中的记录都基于实例来进行持久化。调用DS.Model实例的save()会触发一个网络请求，来进行记录的持久化。

下面是几个示例：

var post = store.createRecord('post', {
  title: 'Rails is Omakase',
  body: 'Lorem ipsum'
});
post.save(); // => POST to '/posts'

var post = store.find('post', 1);
post.get('title') // => "Rails is Omakase"
post.set('title', 'A new post');
post.save(); // => PUT to '/posts/1'

承诺

save()会返回一个承诺，这使得可以非常容易的来处理保存成功和失败的场景。下面是一个通用的模式：

var post = store.createRecord('post', {
  title: 'Rails is Omakase',
  body: 'Lorem ipsum'
});
var self = this;
function transitionToPost(post) {
  self.transitionToRoute('posts.show', post);
}
function failure(reason) {
  // handle the error
}
post.save().then(transitionToPost).catch(failure);
// => POST to '/posts'
// => transitioning to posts.show route

对于失败的网络请求，承诺也可以方便的来处理：

var post = store.createRecord('post', {
  title: 'Rails is Omakase',
  body: 'Lorem ipsum'
});
var onSuccess = function(post) {
  this.transitionToRoute('posts.show', post);
};
var onFail = function(post) {
  // deal with the failure here
};
post.save().then(onSuccess, onFail);
// => POST to '/posts'
// => transitioning to posts.show route

更多关于承诺的内容请参看这里，下面是一个示例展示了如何在重试失败的持久化操作：

function retry(callback, nTimes) {
  // if the promise fails
  return callback().fail(function(reason) {
    // if we haven't hit the retry limit
    if (nTimes-- > 0) {
      // retry again with the result of calling the retry callback
      // and the new retry limit
      return retry(callback, nTimes);
    }
    // otherwise, if we hit the retry limit, rethrow the error
    throw reason;
  });
}
// try to save the post up to 5 times
retry(function() {
  return post.save();
}, 5);