async.apply for mongodb 聚合函数失败

Question

我尝试借助异步库将我的回调地狱代码转换为更加结构化的代码。现在，我有以下代码：

db.collection('campaigns').aggregate(pipeline, function(err, campaigns) {
   capCampaigns(campaigns, function(err, cappedCampaigns) {
     // etc  
   }
});

我改写为

async.waterfall([
  async.apply(db.collection('campaigns').aggregate, pipeline),
  capCampaigns,
 // etc
], function(err, result) {

}

遗憾的是，async.apply 失败了：

TypeError: Cannot read property 's' of null
    at Collection.aggregate (/home/beryllium/sitesrv/node_modules/mongodb/lib/collection.js:2458:35)
    at /home/beryllium/sitesrv/node_modules/async/lib/async.js:760:23
    at /home/beryllium/sitesrv/node_modules/async/lib/async.js:166:37
    at fn (/home/beryllium/sitesrv/node_modules/async/lib/async.js:746:34)
    at /home/beryllium/sitesrv/node_modules/async/lib/async.js:1213:16
    at /home/beryllium/sitesrv/node_modules/async/lib/async.js:166:37
    at /home/beryllium/sitesrv/node_modules/async/lib/async.js:706:43
    at /home/beryllium/sitesrv/node_modules/async/lib/async.js:167:37
    at Object.async.waterfall (/home/beryllium/sitesrv/node_modules/async/lib/async.js:710:44)
    at chooseCampaignAndBanner (/home/beryllium/sitesrv/routes/banner.js:207:9)

我做错了什么？

附加信息： 节点版本：5.7.1 NOdeJS 的 MonogDB 驱动程序：2.1.2

mongo失败的行：

// Build the command
  var command = { aggregate : this.s.name, pipeline : pipeline};

Answer 1

此处的代码将立即将管道应用于聚合方法，而且，它无法在您的代码中进行回调。试试这个：

async.waterfall(
  [
    function(cb) { return db.collection('campaigns').aggregate(pipeline, cb) },
    capCampaigns,
  ], 
  function(err, result) {
  }
)

async.apply for mongodb 聚合函数失败

async.apply for mongodb aggregate function fails

mongodb

node.js

aggregation-framework

async.js