mongoose revision plugin

example.js

var mongoose = require('mongoose')
  , revision = require('..')
  , Schema = mongoose.Schema;

mongoose.connect('localhost', 'sandbox');

var schema = new Schema({
  title: String,
  content: String
});

schema.plugin(revision);

var Post = mongoose.model('Post', schema);

Post.findOne({ title: 'js 101' }, function(err, post){
  if (err) return done(err);
  if (!post) post = new Post({ title: 'js 101' });
  next(post);
});

function next(post){
  post.content = String(Date.now());
  post.save(done);
}

function done(err, post){
  if (err) throw err
  else console.log('post: %j', post);
}

revision.js

function revision(schema, options){
  schema.add({ revision: { type: Number, default: 1 }});

  schema.pre('save', function(next){
    if (!this.isModified()) return next();

    var self = this
      , db = this.db
      , shadow = this.toObject()
      , name = this.constructor.collection.collection.collectionName
      , collection = db.collection(name + '_revisions');
    
    shadow._id = {
      _id: this.id,
      revision: this.revision
    };

    collection.insert(shadow, function(err){
      if (err) return next(err);
      self.revision += 1;
      next();
    });
  });
}