Question

我很抱歉这个模糊的标题和长篇文章，但我很难描述我得到的行为。我会尝试任何一种方式来解释。

我有一个新闻源页面，我正在显示帖子。我只想显示比用户打开页面时更旧的帖子，这样列表就会保持被动，而不会在顶部添加新帖子。所以我决定在发布函数中使用observeChanges，如下所示：

Newsfeed = new Mongo.Collection('newsfeed');

if (Meteor.isServer) {
    Meteor.publish("newsfeed", function (init_last_activity, limit) {
        var self = this;

        check(limit, Number);
        check(init_last_activity, Date);

        var init = true,
            count = 0;

        var handle = Newsfeed.find({},{
            'limit': limit,
            'sort': {'updated_time': -1}
        }).observeChanges({
            // when a post is added, we check if it's got an older
            // updated_time than the initial updated time field
            // generated on init and only if so, we display
            // the post to the client
            added: function(id, doc) {
                count++;
                console.log('++++ POST NR. ' + count + ' ++++ ('+id+')');
                console.log('Updated time:  ', doc.updated_time);
                console.log('Last activity: ', init_last_activity);

                if (doc.updated_time < init_last_activity) {
                    console.log('- - - - -');
                    console.log('ADDED!');

                    self.added('newsfeed', id, doc);

                    console.log('ID: ' + id);
                    console.log(' ');
                }
            },

            changed: function(id, fields) {
                console.log('Trigger changed for id:', id);
                self.changed('newsfeed', id, fields);
            }
        });

        init = false;

        this.ready();

        this.onStop(function() {
            handle.stop();
        });
    });
}

包含控制台日志，以说明实际上正在调用self.added()。以下是用户刷新页面时的日志：

I20141024-20:21:08.886(-7)? ++++ POST NR. 1 ++++ (9WMnDt5tJ6wePwfcs)
I20141024-20:21:08.887(-7)? Updated time:   Fri Oct 24 2014 20:17:47 GMT-0700 (PDT)
I20141024-20:21:08.887(-7)? Last activity:  Fri Oct 24 2014 20:21:08 GMT-0700 (PDT)
I20141024-20:21:08.887(-7)? - - - - -
I20141024-20:21:08.887(-7)? ADDED!
I20141024-20:21:08.887(-7)? ID: 9WMnDt5tJ6wePwfcs
I20141024-20:21:08.887(-7)?
I20141024-20:21:08.887(-7)? ++++ POST NR. 2 ++++ (7pt3nBKqgCKJ4G5fc)
I20141024-20:21:08.887(-7)? Updated time:   Fri Oct 24 2014 20:20:59 GMT-0700 (PDT)
I20141024-20:21:08.888(-7)? Last activity:  Fri Oct 24 2014 20:21:08 GMT-0700 (PDT)
I20141024-20:21:08.888(-7)? - - - - -
I20141024-20:21:08.888(-7)? ADDED!
I20141024-20:21:08.888(-7)? ID: 7pt3nBKqgCKJ4G5fc
I20141024-20:21:08.888(-7)?

如您所见，已向客户发送了两个帖子。现在，当同一个用户尝试“喜欢”第二篇帖子（ID: 7pt3nBKqgCKJ4G5fc）时，几秒钟之后，这会在上面的代码中触发self.changed()，这种情况会发生：

I20141024-20:21:13.997(-7)? Trigger changed for id: 7pt3nBKqgCKJ4G5fc
I20141024-20:21:13.997(-7)? Exception in queued task: Error: Could not find element with id 7pt3nBKqgCKJ4G5fc to change
I20141024-20:21:13.997(-7)?     at _.extend.changed (packages/ddp/livedata_server.js:185)
I20141024-20:21:13.997(-7)?     at _.extend.changed (packages/ddp/livedata_server.js:397)
I20141024-20:21:13.997(-7)?     at _.extend.changed (packages/ddp/livedata_server.js:1154)
I20141024-20:21:13.997(-7)?     at Newsfeed.find.observeChanges.changed (app/collections/newsfeed.js:125:22)
I20141024-20:21:13.998(-7)?     at packages/mongo/observe_multiplex.js:163
I20141024-20:21:13.998(-7)?     at Array.forEach (native)
I20141024-20:21:13.998(-7)?     at Function._.each._.forEach (packages/underscore/underscore.js:105)
I20141024-20:21:13.998(-7)?     at Object.task (packages/mongo/observe_multiplex.js:157)
I20141024-20:21:13.998(-7)?     at _.extend._run (packages/meteor/fiber_helpers.js:145)
I20141024-20:21:13.998(-7)?     at packages/meteor/fiber_helpers.js:123

几秒钟之前附加到self.added()函数的完全相同的ID。奇怪的是，如果我跳过if语句并且只允许self.added()运行，无论如何，一切正常：

added: function(id, doc) {
    self.added('newsfeed', id, doc);
}

所以，虽然在前面的例子中调用self.added()，但似乎只是因为它在if语句中被调用会破坏代码。

有没有人知道为什么会这样？我是否误解了添加和更改的功能？我很困惑:)）

在Meteor中，this.added和this.changed在observeChanges内运行不正常

0 个答案: