如何在 Meteor.js 中的服务器端转换函数后设置 mongo 投影？

Question

在应用需要访问原始文档的转换后，我需要限制从发布函数发送到客户端的字段数。

我基本上是在尝试避免向客户端发送可能很大的数组，并且运行一堆检查 return 一个很好的整洁对象。

这是我现在得到的功能 - 它可以工作，只是不是我想要的方式，基本上限制了观察功能的字段。有没有办法在观察/变换之后添加投影。

Meteor.publish('network', function() {

  var self = this;

  // get the user values initially
  var user = Meteor.users.findOne(self.userId);
  var followingUsers = user.following ? user.following.users || [] : [];
  var followingChannels = user.following ? user.following.channels || [] : [];

  var transformMedia = function(doc) {
    // get the user each time to keep this publication reactive
    votesUp = doc.votes ? doc.votes.up || [] : [];
    votesDown = doc.votes ? doc.votes.down || [] : [];
    favourites = doc.votes ? doc.votes.favourites || [] : [];

    doc.userActions = {
      votedUp: _.contains(votesUp, doc._id) ? 1 : 0,
      votedDown: _.contains(votesDown, doc._id) ? 1 : 0,
      isFavourite: _.contains(favourites, doc._id) ? 1 : 0,
      played: _.contains(doc.played, self.userId) ? 1 : 0,
    };

    return doc;
  };

  var networkQuery = Media.find({
    $and: [
    {
        $and: [
          {processedAt: { $exists: true} },
          {processedStatus: 'successful'},
          {publishStatus: 'published'}
        ]
      },
      {
        // if created by this user, user they follow or channels they subscribe to
        $or: [
          {createdBy: self.userId },
          {createdBy: { $in: followingUsers} },
          {channels: { $in: followingChannels} },
        ]
      }

      // TODO : add not banned or trashed once implemented
    ]
  }, mediaModifiers).observe({
    added: function(doc) {
      self.added('media', doc._id, transformMedia(doc));
    },
    changed: function(doc, oldDoc) {
      self.changed('media', doc._id, transformMedia(doc));
    },
    removed: function(doc) {
      self.removed('media', doc._id, transformMedia(doc));
    },
  });

  self.onStop(function() {
    networkQuery.stop();
  });

  self.ready();

});

Answer 1

我有。我使用 cursor.observe()+ 自定义函数（就像你所做的那样）处理它，我只是添加了一个 _.pick() 来过滤不必要的字段。看看这个发布代码的例子（特别是白名单 docToPublish 部分）：

var self = this;

// Modify the document we are sending to the client.
function filter(doc) {
  var length = doc.item.length;

  // White list the fields you want to publish.
  var docToPublish = _.pick(doc, [
      'someOtherField'
  ]);

  // Add your custom fields.
  docToPublish.itemLength = length;

  return docToPublish;                        
}

var handle = myCollection.find({}, {fields: {item:1, someOtherField:1}})
            // Use observe since it gives us the the old and new document when something is changing. 
            // If this becomes a performance issue then consider using observeChanges, 
            // but its usually a lot simpler to use observe in cases like this.
            .observe({
                added: function(doc) {
                    self.added("myCollection", doc._id, filter(doc));
                },
                changed: function(newDocument, oldDocument)
                    // When the item count is changing, send update to client.
                    if (newDocument.item.length !== oldDocument.item.length)
                        self.changed("myCollection", newDocument._id, filter(newDocument));
                },
                removed: function(doc) {
                    self.removed("myCollection", doc._id);                    
                });

self.ready();

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

这段代码是从@datacarl 对我上面提到的主题的回答中借用的。

请注意，如果您扩展到多台服务器，这种方法的缺点是每台服务器都必须运行 cursor.observe() 函数。

您还忘记准备发布并在发布结束时处理您的观察者（这可能是因为您没有粘贴所有发布）。它看起来像这样：

self.ready();
self.onStop(function () {
  networkQuery.stop();
});

如何在 Meteor.js 中的服务器端转换函数后设置 mongo 投影？

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