Reactively publish aggregations with Meteor.
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Reactively publish aggregations.

meteor add jcbernack:reactive-aggregate

This helper can be used to reactively publish the results of an aggregation.


ReactiveAggregate(sub, collection, pipeline, options)
  • sub should always be this in a publication.
  • collection is the Mongo.Collection instance to query.
  • pipeline is the aggregation pipeline to execute.
  • options provides further options:
    • observeSelector can be given to improve efficiency. This selector is used for observing the collection. (e.g. { authorId: { $exists: 1 } })
    • observeOptions can be given to limit fields, further improving efficiency. Ideally used to limit fields on your query. If none is given any change to the collection will cause the aggregation to be reevaluated. (e.g. { limit: 10, sort: { createdAt: -1 } })
    • clientCollection defaults to collection._name but can be overriden to sent the results to a different client-side collection.

Quick Example

A publication for one of the examples in the MongoDB docs would look like this:

Meteor.publish("booksByAuthor", function () {
  ReactiveAggregate(this, Books, [{
    $group: {
      _id: "$author",
      books: { $push: "$$ROOT" }

Extended Example

Define the parent collection you want to run an aggregation on. Let's say:

Reports = new Meteor.Collection('Reports');

.. in a location where all your other collections are defined, say lib/collections.js

Next, prepare to publish the aggregation on the Reports collection into another client-side-only collection we'll call, clientReport.

Create the clientReport in the client side (its needed only for client use). This collection will be the destination in which the aggregation will be put into upon completion.

Now you publish the aggregation on the server:

Meteor.publish("reportTotals", function() {
// Remember, ReactiveAggregate doesn't return anything
ReactiveAggregate(this, Reports, [{
    // assuming our Reports collection have the fields: hours, books
    $group: {
        '_id': this.userId,
        'hours': {
        // In this case, we're running summation. 
            $sum: '$hours'
        'books': {
            $sum: 'books'
}, {
    $project: {
    	// an id can be added here, but when omitted, 
        // it is created automatically on the fly for you
        hours: '$hours',
        books: '$books'
    } // Send the aggregation to the 'clientReport' collection available for client use
}], { clientCollection: "clientReport" });

We therefore need to subscribe to the above Publish.


Then in our Template helper:

    reportTotals: function() {
        console.log("I'm working");
        return clientReport.find();

Finally, your template:

{{#each reportTotals}}Total Hours: {{hours}} <br/>Total Books: {{books}}{{/each}}

Your aggregated values will therefore be available in client-side and behave reactively just as you'd expect.

Enjoy aggregating reactively!