get an object from redis, modify contents, and set

getset.js

  var Bluebird = require('bluebird');
  var redis = require('redis');
  var _ = require('lodash');
  
   function getSet(key, transmute){
      return new Bluebird(function(resolve, reject){
         function setAtomic(key, count){
            var counts = count;

            // create a UNIQUE CLIENT CONNECTION for this process
            var atomicClient = redis.createClient();
            atomicClient.watch(key);

            // get the object
            atomicClient.hgetall(key, function(err,o){
               var newO = {};
               if(err){
                  return reject(err);
               }

               // get parsed object
               var generated = Object.keys(o).reduce(function(generated, field){
                  var val;
                  try {
                     val = JSON.parse(o[field]);
                  }
                  catch (e){
                     val = '';
                  }
                  generated[field] = val;
                  return generated;
               },{});

               // run the transmute function
               newO = transmute(generated);

               // update all keys
               var chain = Object.keys(newO).reduce(function(ch, field){
                  var val = typeof newO[field] === 'string' ? newO[field] : JSON.stringify(newO[field]);
                  return ch.hset(key, field, val);
               }, atomicClient.multi());

               var k1 = Object.keys(o);
               var k2 = Object.keys(newO);
               
               // remove the keys from redis that are no longer in the object (after transmuting)
               var keysToRemove = _.difference(k1, k2);
               var nextChain = keysToRemove.reduce(function(ch, field){
                  return ch.hdel(key, field);
               }, chain);

               nextChain.hgetall(key).exec(function(err, results){
                  atomicClient.quit();
                  if(results === null && counts < 10){
                     setAtomic(key, counts++);
                  }
                  if(results === null && counts >= 10){
                     return reject(new Error("Could not complete transaction"));
                  }
                  if(err){
                     return reject(err);
                  }
                  return resolve(results);
               });
            });
         }
         setAtomic(key, 0);
      });
   }