Meteor:我怎么知道数据库什么时候准备好? [英] Meteor: How can I tell when the database is ready?

问题描述

我想在页面加载后尽快执行 Meteor 集合查询.我尝试的第一件事是这样的:

I want to perform a Meteor collection query as soon as possible after page-load. The first thing I tried was something like this:

Games = new Meteor.Collection("games");
if (Meteor.isClient) {
  Meteor.startup(function() {
    console.log(Games.findOne({}));
  }); 
}

但这不起作用(它打印未定义").当从 JavaScript 控制台调用时，相同的查询会在几秒钟后生效.我认为在数据库准备好之前存在某种滞后.那么我怎么知道这个查询什么时候会成功呢?

This doesn't work, though (it prints "undefined"). The same query works a few seconds later when invoked from the JavaScript console. I assume there's some kind of lag before the database is ready. So how can I tell when this query will succeed?

OSX 10.8 和 Chrome 25 下的流星版本 0.5.7 (7b1bf062b9).

Meteor version 0.5.7 (7b1bf062b9) under OSX 10.8 and Chrome 25.

推荐答案

您应该首先发布来自服务器的数据.

You should first publish the data from the server.

if(Meteor.isServer) {
    Meteor.publish('default_db_data', function(){
        return Games.find({});
    });
}

在客户端，只有在从服务器加载数据后才执行集合查询.这可以通过在 subscribe 调用中使用反应式会话来完成.

On the client, perform the collection queries only after the data have been loaded from the server. This can be done by using a reactive session inside the subscribe calls.

if (Meteor.isClient) {
  Meteor.startup(function() {
     Session.set('data_loaded', false); 
  }); 

  Meteor.subscribe('default_db_data', function(){
     //Set the reactive session as true to indicate that the data have been loaded
     Session.set('data_loaded', true); 
  });
}

现在，当您执行集合查询时，您可以检查数据是否已加载:

Now when you perform collection queries, you can check if the data is loaded or not as:

if(Session.get('data_loaded')){
     Games.find({});
}

注意:删除 autopublish 包，它默认将您的所有数据发布到客户端，这是不好的做法.

Note: Remove autopublish package, it publishes all your data by default to the client and is poor practice.

要删除它，请从根项目目录对每个项目执行 $meteor remove autopublish.

To remove it, execute $ meteor remove autopublish on every project from the root project directory.

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