Article: Sorting with Relations in Meteor

sorting-with-relations-5.js

var defineRelation = function(
	Collection, RelatedCollection, relationName, relatedFieldName
) {
	Collection._computations = Collection._computations || {};
	var comps = Collection._computations[relationName] = {};

	var stop = function(doc) {
		if (comps[doc._id]) {
			comps[doc._id].stop();
		}
	};

	var update = function(doc) {
		var setModifier = {};

		setModifier[relationName] = doc[relatedFieldName] ?
			RelatedCollection.findOne(doc[relatedFieldName]) : undefined;

		Collection._collection.update(doc._id, {
			$set: setModifier
		});
	};

	Collection.find().observe({
		added: function(newDoc) {
			stop(newDoc);
			comps[newDoc._id] = Tracker.autorun(function() {
				update(newDoc);
			});
		},
		changed: function(newDoc, oldDoc) {
			if (newDoc[relatedFieldName] !== oldDoc[relatedFieldName]) {
				stop(oldDoc);
				comps[newDoc._id] = Tracker.autorun(function() {
					update(newDoc);
				});
			}
		},
		removed: function(oldDoc) {
			stop(oldDoc);
		}
	});
};