Use publish/subscribe with database persistence to cache on the application server (high read data)

pub-sub-configs.js

// In some situations, you want the "configuration" to be persistent and dynamic. For example, a 
// web site with dynamic forms.
// There are multiple ways of making this work...
// - Store it in the database and access it when you need it; very poor performance.
// - Store it in the database and cache the data directly in the application server. Update
// every now and then; better performance, but not very clean considering you will need to wait
// for the configuration changes to take effect.
// - Use pud/sub; best performance and changes are instantaneous.
function reactiveDataPool(seneca, pgClient, entityName, query, done) {
	var pushAll = function(arr, items) {
		for(var i = 0; i < items.length; i++) arr.push(item[i]);
	};

	var indexOfId = function(arr, id) {
		for(var i = 0; i < arr.length; i++) {
			if(arr[i].id === id) return i;
		}
		return -1;
	};

	var pool = [];
	// initial load of the data from the DB.
	seneca
		.make(entityName)
		.load$(query, function(err, ents) {
			if(err) return done(err);

			pushAll(pool, ents);

			// create the names for the events.
			var snake = _.snakeCase(entityName);
			var delEv = 'delete_' + snake;
			var addEv = 'add_' + snake;
			var updateEv = 'update_' + snake;

			pgClient.on('notification', function(msg) {
				var data = JSON.parse(msg.payload);
				var event = msg.channel;
				if(event === addEv) {
					pool.push(data);
				} else if(event === delEv) {
					var i = indexOfId(pool, data.id);
					pool.splice(i, 1);
				} else if(event === updateEv) {
					var i = indexOfId(pool, data.id);
					pool[i] = data;
				}
			});

			[delEv, addEv, updateEv].forEach(function(event) {
				pgClient.query('LISTEN ' + event);
			});

			done(null, pool);

		});
}