Meteor:发布数组元素的 2 个不同投影 [英] Meteor: publish 2 different projections of array elements

问题描述

我在一个集合中有这样的元素:

I have elements like this one in a collection:

{
    array: [{ a:10, b: {...} }, { a:30, b: {...} }, { a:50 b: {...} }]
}

在一个可以返回数百个结果的出版物中，我将数组投影到只有 a 字段并且重量更轻:

In one publication, that can return hundreds of results, I project the array to only have the a field and weigh less:

return Col.find({}, { fields: { 'array.a': 1 } })

在另一篇文章中，我发布了一个完整的文档:

In another one, I publish a single full document:

return Col.find({ _id: ObjectId(...) })

第二次发布缺少从每个数组项中排除的字段第一次发布，有时.刷新页面(可能会改变订阅顺序?)修复了错误.

The 2nd publication is missing the fields excluded from each array item in the first publication, sometimes. Refreshing the page (perhaps changing the order of subscriptions?) fixes the bug.

如何在我的大型出版物中发布减少的数组项，以及完整的单个出版物中的元素?

How can I publish reduced array items in my large publication, and the full elements in the single publication?

推荐答案

我研究了不同的方法.该问题可以通过仔细选择字段和注意订阅顺序逐案解决，但这些解决方案是站不住脚的，并且依赖于未记录的任意条件.

I examined different approaches. The problem can be solved on a case-by-case basis by carefully picking fields and minding subscription order, but these solutions are flimsy and rely on non-documented arbitrary conditions.

唯一真正通用的解决方案是虚拟收藏.最简单的情况是简单地在不同的客户端集合名称下发布游标.例如:

The only real, generic solution is a virtual collection. The simplest case is simply publishing a cursor under a different, client-side collection name. For example:

function publishVirtual(sub, name, cursor) {
  var observer = cursor.observeChanges({
    added  : function(id, fields) { sub.added(name, id, fields) },
    changed: function(id, fields) { sub.changed(name, id, fields) },
    removed: function(id)         { sub.remove(name, id) }
  })

  sub.onStop(function() {
    observer.stop() // important. Otherwise, it keeps running forever
  })
}

然后，在您的出版物中，而不是返回 cursor:

And then, in your publication, instead of returning a cursor:

var cursor = Users.find()
publishVirtual(this, 'virtualUsers', cursor)
this.ready()

这篇关于Meteor:发布数组元素的 2 个不同投影的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！