当我在其中调用的集合更新时，为什么我的助手没有重新 运行？
Why my helper doesn't re-run when the collection I call inside it is updated?
我有一个带有视频播放器的模板。它使用帮助程序从 mongo 文档获取视频源。这是它的样子：
帮手：
'currentItemUrl' : function() {
//I only have one project. Is there a better/cleaner way to obtain it than the one below?
var currentProject = Projects.find().fetch()[0];
//the function below will create an instance of videojs or update the current one (set the new source)
loadPlayer();
//I return the source url if I have one
return currentProject.setup.player.item_loaded.url?currentProject.setup.player.item_loaded.url:"";
}
HTML 看起来像这样：
<video id="video_player" class="video-js vjs-default-skin" controls preload="auto"
width = "{{videoWidth}}" height="videoHeight"
poster="{{currentItemPoster}}">
<source id="mp4" src="{{currentItemUrl}}" type='video/mp4' />
<source id="webm" src="" type='video/webm' />
<source id="ogg" src="" type='video/ogg' />
</video>
问题
当我在另一个模板中更新我的 Projects 集合时，我如何确保我的助手是 re-运行？因为我使用 Collection.find() 它不应该是反应式的吗？
关于你的第一个问题（在你的代码的注释中），如果你在任何时间点只有一个文档，那么 findOne:
有一个更简单的方法
var currentProject = Projects.findOne();
您可以简单地使用 || operator 而不是默认的重三元组：
//Always place the default on the right, since '' is falsey
return (currentProject.setup.player.item_loaded.url || '');
并且因为您使用 find（或 findOne 除了它 returns 一个文档之外基本上是相同的东西）它总是反应性的。如果文档发生变化，那么 Tracker 计算将失效并且您的助手 uses such a computation :
Under the hood, each helper starts a new Tracker.autorun. When its reactive dependencies change, the helper is rerun. Helpers depend on their data context, passed arguments and other reactive data sources accessed during execution.
不过，作为apendua noted in a comment, your helper triggers side-effects (loadPlayer()) - This is generally considered a bad practice because a helper is very similar to a getter: You just expect it to return data, not alter anything. You may want to run another Tracker computation这份工作。
我有一个带有视频播放器的模板。它使用帮助程序从 mongo 文档获取视频源。这是它的样子：
帮手：
'currentItemUrl' : function() {
//I only have one project. Is there a better/cleaner way to obtain it than the one below?
var currentProject = Projects.find().fetch()[0];
//the function below will create an instance of videojs or update the current one (set the new source)
loadPlayer();
//I return the source url if I have one
return currentProject.setup.player.item_loaded.url?currentProject.setup.player.item_loaded.url:"";
}
HTML 看起来像这样：
<video id="video_player" class="video-js vjs-default-skin" controls preload="auto"
width = "{{videoWidth}}" height="videoHeight"
poster="{{currentItemPoster}}">
<source id="mp4" src="{{currentItemUrl}}" type='video/mp4' />
<source id="webm" src="" type='video/webm' />
<source id="ogg" src="" type='video/ogg' />
</video>
问题
当我在另一个模板中更新我的 Projects 集合时，我如何确保我的助手是 re-运行？因为我使用 Collection.find() 它不应该是反应式的吗？
关于你的第一个问题（在你的代码的注释中），如果你在任何时间点只有一个文档，那么 findOne:
var currentProject = Projects.findOne();
您可以简单地使用 || operator 而不是默认的重三元组：
//Always place the default on the right, since '' is falsey
return (currentProject.setup.player.item_loaded.url || '');
并且因为您使用 find（或 findOne 除了它 returns 一个文档之外基本上是相同的东西）它总是反应性的。如果文档发生变化，那么 Tracker 计算将失效并且您的助手 uses such a computation :
Under the hood, each helper starts a new Tracker.autorun. When its reactive dependencies change, the helper is rerun. Helpers depend on their data context, passed arguments and other reactive data sources accessed during execution.
不过，作为apendua noted in a comment, your helper triggers side-effects (loadPlayer()) - This is generally considered a bad practice because a helper is very similar to a getter: You just expect it to return data, not alter anything. You may want to run another Tracker computation这份工作。