Ember.js：计算所有子模型的属性的总和 [英] Ember.js: Calculate the sum of a property of all child models
问题描述
我的应用程序有以下型号：
My application has the following models:
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？
How can I calculate the sum of all App.User.tweetsUnread and make it automatically update App.List.tweetsUnread?
推荐答案
以下应该做到。可能有一个更简洁的解决方案，使用reduce，但我从来没有使用过自己： - ）
The following should do it. There might be an more concise solution using reduce, but i have never used it myself :-)
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。我从来没有使用过它，但这并没有被测试，但我相信这应该是有效的：
Update: This is a more elegant solution using reduce. I have never used it and this isn't tested but i am quite confident that this should work:
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，用于reduce的API已更改！ Thx @joelcox for提示，参数initialValue和回调已经改变了他们的位置。所以这里代码的正确版本：
In Ember 1.1 the API for reduce has changed! Thx @joelcox for the hint, that the parameters initialValue and callback have changed their position. So here the correct version of the code:
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")
});
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