mongodb-counter

This is a trivial mongodb auto-increment counter implementation based on MongoDB Documentation.

But this implementation requires Mongo 2.4 because it uses the $setOnInsert operation. Unlike the sample in the documentation, this will allow creating new counters on the fly without initializing the counters to zero.

Install

npm install mongodb-counter

Initialization

   // Initialization via mongo URLs of the form: mongodb://user:password@host:port/database
   var counters = require('mongodb-counter').createCounters({mongoUrl: 'mongodb://user:password@host:port/database'});

   // Specifying collection name instead of defaulting to counters collection
   var counters = require('mongodb-counter').createCounters({
     mongoUrl: 'mongodb://user:password@host:port/database',
     collectionName: 'yoyo'
   });

   // Initialization via a pre-created database collection to use
   var counters = require('mongodb-counter').createCounters({collection: db.counters});

API

   counters('requests').increment(); // increments by one, throws away the result
   counters('requests').increment(5); // increments by 5 throws away the result
   counters('requests').increment(5, function (err, currentCount) {
     // currentCount is the updated count.
   });

   // increment by one and get the new value
   counters('requests').increment(function (err, currentCount) {
     // currentCount is the updated count.
   });

   counters('requests').decrement(); // same options with decrement
   counters('requests').get(function (err, val) {
     // fetch the current value
   });
   counters('requests').set(52); // update the value.

   // if you only want to generate unique ids (for URL shortening for example),
   // a much faster method is getNextUniqueId.  It only hits the database every 100
   // calls.  Ofcourse, this has the side effect that the sequence is not strictly
   // monotonically increasing in order and there could be gaps when there are crashes
   // but uniqueness is guaranteed and the ordering will be almost monotonic.  This is
   // suitable for a lot of cases where you just want a small unique ID.

   function getShortUrl(longUrl, done) {
     counters('requests').getNextUniqueId(function (err, uniqueId) {
       if (err) return done(err);
       var shortUrl = '/' + uniqueId.toString(36);
       db.shortUrls.insert(
         {shortUrl: '/' + uniqueId.toString(36), longUrl: longUrl},
         function (err) { return done(err, !err && shortUrl); }
       );
     });
   });