Ember.js:计算所有子模型的属性之和

Question

我的应用程序有以下型号:

App.Store = DS.Store.extend({
    revision: 11,
    adapter: 'DS.FixtureAdapter'
});

App.List = DS.Model.extend({
    name: DS.attr('string'),
    users: DS.hasMany('App.User'),
    tweetsUnread: function(){
        /////////////////////////////////////////
        // Code to dynamically calculate the sum 
        // of tweetsUnread property of all
        // App.User that are related to this list
        /////////////////////////////////////////
    }
});

App.User = DS.Model.extend({
    screenName: DS.attr('string'),
    tweets: DS.hasMany('App.Tweet'),
    tweetsUnread: function(){
        // TODO: check if this is the correct way to do it
        return this.get('tweets').get('length');
    }.property('tweets.@each'),
    list: DS.belongsTo('App.List')
});

App.Tweet = DS.Model.extend({
    text: DS.attr('string'),
    user: DS.belongsTo('App.User')
});

如何计算所有App.User.tweetsUnread的总和并使其自动更新App.List.tweetsUnread？

Answer 1

另一个选择是使用这里Ember.computed.sum看到

App.List = DS.Model.extend({
  name: DS.attr('string'),
  users: DS.hasMany('App.User'),

  tweetsUnread: Ember.computed.mapBy('users', 'tweetsUnread'),
  totalTweetsUnread: Ember.computed.sum('tweetsUnread')   
});

Answer 2

以下应该这样做.使用reduce可能有一个更简洁的解决方案,但我自己从未使用过它:-)

App.List = DS.Model.extend({
    name: DS.attr('string'),
    users: DS.hasMany('App.User'),
    tweetsUnread: function(){
        var users = this.get("users");
        var ret = 0;
        users.forEach(function(user){
            ret += users.get("tweetsUnread");
        });
        return ret;
    }.property("users.@each.tweetsUnread")
});

更新:这是使用reduce的更优雅的解决方案.我从来没有使用它,这没有测试,但我相信这应该工作:

App.List = DS.Model.extend({
    name: DS.attr('string'),
    users: DS.hasMany('App.User'),
    tweetsUnread: function(){
        var users = this.get("users");
        return users.reduce(0, function(previousValue, user){
            return previousValue + users.get("tweetsUnread");
        });
    }.property("users.@each.tweetsUnread")
});

在Ember 1.1中,reduce的API已经改变了!对于提示,@ joelcox,参数initialValue和callback已经改变了它们的位置.所以这里是正确的代码版本:

App.List = DS.Model.extend({
    name: DS.attr('string'),
    users: DS.hasMany('App.User'),
    tweetsUnread: function(){
        var users = this.get("users");
        return users.reduce(function(previousValue, user){
            return previousValue + user.get("tweetsUnread");
        }, 0);
    }.property("users.@each.tweetsUnread")
});