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 bethis
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 tocollection._name
but can be overriden to sent the results to a different client-side collection.
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" }
}
}]);
});
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.
Meteor.subscribe("reportTotals");
Then in our Template helper:
Template.statsBrief.helpers({
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
!