Meteor aggregation

publication.coffee

Meteor.publishAggregation = (params) ->
  initializing = true
  dummy = Random.id()
  pub = params.handle
  collection = params.collection
  handle = collection.find(params.filter, params.options).observeChanges
    added: (id, fields) ->
      if !initializing
        pub.changed(params.name, dummy, collection.aggregate(params.pipeline)[0])

    removed: (id) ->
      pub.changed(params.name, dummy, collection.aggregate(params.pipeline)[0])

  initializing = false
  pub.added(params.name, dummy, collection.aggregate(params.pipeline)[0])
  pub.ready()
  pub.onStop -> handle.stop()

Meteor.publish 'avgMeetingsCreated', ->
  sum =
    $group:
      _id: '$userId'
      sum:
        '$sum': 1

  avg =
    $group:
      _id: null
      avg:
        '$avg': '$sum'

  Meteor.publishAggregation
    handle: this
    name: 'avgMeetingsCreated'
    collection: Meetings
    pipeline: [sum, avg]
    filter: {}