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POnode.js fall through data cache pattern
 

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    <p>I am looking for a clean way to structure my node.js code for the following situation. I thought of using EventEmitters to create a "workflow" type of thing. Also I thought of using one of the async libraries out there, that has been less thought out though.</p> <p>Problem: Looking for a piece of data</p> <ol> <li>check cache, if found return</li> <li>check db, if found return (store in cache)</li> <li>get live data and return, (store in db, cache)</li> </ol> <p>I mocked something up quickly using event emitters below.</p> <pre><code>var util = require("util"); var events = require('events'); var CheckForData = function() { events.EventEmitter.call(this); this.checkForData = function(key) { this.emit("checkForDataRequest", key); } var _checkCache = function(key) { if (key === 'cache') { this.emit("found", {data:'cached data'}); } else { console.log("not found in cache "+key); this.emit("checkDatastore", key); } } var _chechDatastore = function(key) { if (key === 'db') { this.emit("found", {data:'db data'}); this.emit("storeCache", key, {data:'db data'}); } else { console.log("not found in db "+key); this.emit("getData", key); } } var _getData = function(key) { if (key === 'live') { this.emit("found", {data:'live data'}); this.emit("storeData", key, {data:'live data'}); } else { console.log("not found in live "+key); this.emit("notFound", key); } } var _storeData = function(key, data) { this.emit("storeDb", key, data); this.emit("storeCache", key, data); } var _storeDb = function(key, data) { console.log("storing data in db. for "+key); console.log(data); } var _storeCache = function(key, data) { console.log("storing data in cache. for "+key); console.log(data); } var _found = function(data) { return data; } var _notFound = function(key) { return key; } this.on("checkForDataRequest", _checkCache); this.on("checkDatastore", _chechDatastore); this.on("getData", _getData); this.on("found", _found); this.on("notFound", _notFound); this.on("storeData", _storeData); this.on("storeDb", _storeDb); this.on("storeCache", _storeCache); }; util.inherits(CheckForData, events.EventEmitter); module.exports = new CheckForData(); </code></pre> <p>To test it...</p> <pre><code>var checkForData = require('./check-for-data'); checkForData.on("found", function(data) { console.log("Found data "); console.log(data); }); checkForData.on("notFound", function(key) { console.log("NOOO Found data for " + key); }); console.log("-------"); checkForData.checkForData('cache'); console.log("-------"); checkForData.checkForData('db'); console.log("-------"); checkForData.checkForData('live'); console.log("-------"); checkForData.checkForData('other'); console.log("-------"); </code></pre> <hr> <p>Then async.js, i made a quick checkSeries which is basically the async.detectSeries but instead of returning the item in the collection return the result. See below...</p> <pre><code>var async = require('async'); function check_cache(key) { console.log('checking cache'); return null; } function check_datastore(key) { console.log('checking datastore'); return null;//{data: "db data"}; } function check_api(options) { console.log('calling api'); return {data: "live data"}; } function exists(item, callback) { callback(item()); } async.checkSeries([check_cache, check_datastore, check_api], exists, function(result) { // result now equals the first function that return data console.log(result); }); </code></pre> <p>Any suggestions, hints, tips, ...? Is there a pattern or library that i am missing? Do you think it be possible/easier to do in Step, flow, ...? Memoize?</p>
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