MongoDB how to delete temporary collection after operations finish - mongodb

Question

Sometimes I create a temporary collection to aggregate data from multiple collections into a single collection for reporting. I need to drop this temporary collection shortly after a report is created to avoid filling up disk space with temporary collections from many report requests.
Currently I execute this from the application
db.dropCollection('tempCollection564e1f5a4abea9100523ade5');
but the results are not consistent each time it runs. Sometimes the collection drops successfully, but other times the collection fails to drop with this error message:
MongoError: exception: cannot perform operation: a background operation is currently running for collection databaseName.tempCollectionName
code: 12587
What is a best practice for deleting temporary collections in MongoDB? I currently name the collection with a UUID to avoid name collisions, and the collection is only used once before I attempt to destroy the temporary collection.
Is there a way to check if operations are in progress for a collection, and then drop the collection when the operations complete?
note: I do not believe this is an issue with javascript async code in the application. I call the dropCollection() after the aggregation query completes.

Answer 1

I ended up creating this mongoose plugin, and it's been running great in production for over a year. I create a temporary collection, then use setTimeout() to drop the collection 1 minute later. 1 minute is sufficient to query the collection, so the collection is no longer in use.
This creates collections with unique names, such as z_tempCollection_595820e4ae61ecc89635f794, so there is never a name collision.
var mongoose = require('mongoose');
var _ = require('lodash');
var util1 = require(global.appRootPath + '/lib/util1_lib.js');
function tempCollection(persistantSchema){
persistantSchema.statics.resultIntoTempCollection = function (tempCollectionDataArray, options, callback) {
var timestampSeconds = Math.round(Date.now() / 1000);
var tmpCollectionName = 'z_tempCollection_' + (new mongoose.mongo.ObjectId().toString()) + '_' + timestampSeconds;
var registeredModelName = 'tempModel' + tmpCollectionName;
options = options || {};
options.strict = _.isUndefined(options.strict) ? false : options.strict;
options.schema = _.isUndefined(options.schema) ? {} : options.schema;
var tmpSchema = new mongoose.Schema(options.schema, {strict: options.strict, collection: tmpCollectionName});
tmpSchema.statics.removeTempCollection = function(tempModel){
var maxRemovalAttempts = 3;
delete mongoose.models[registeredModelName];
delete mongoose.modelSchemas[registeredModelName];
setTimeout(function(){
mongoose.connection.db.dropCollection(tmpCollectionName, function (err, result) {
if (err) {
util1.saveError(err, 'server', null);
}
});
}, 60 * 1000);
}
// tempModel variable ref is overwritten on each subsequent run of resultIntoTempCollection
var tempModel = mongoose.model(registeredModelName, tmpSchema);
var promises = [];
tempCollectionDataArray.forEach(function(doc){
promises.push(new tempModel(doc).save());
});
return Promise.all(promises).then(function(){
return tempModel;
});
}
}
module.exports = tempCollection;