data_access.md

Data Access Layer

Overview

The concept of a data access layer is to provide a single entry point for all clients to access SleeperBot Data securely in a way that is language agnostic.

How does it work?

The data access layer is in its current form a single node.js process residing on the same server as the master database that holds all the business logic calls to the database.

The data access layer accepts 0mq requests and sends 0mq replies back to the calls origination once data is fetched from our database (or cache).

Protocol API for the Data Access Layer

We will use 0mq to handle all communication.
Requests and replies are all handled in JSON format.

Sample Request located in lib/mq.coffee

{
	id: <uuid>,
	method: 'User:getNameById',
	params: {param1: 'param1', param2: 'param2' ...}
}

Sample Response

{
	id: <uuid>,
	data: data // data from DB
}

Sample Client API from Web Server

** sending data **

query.send({
	id: <uuid>,
	method: 'User:getNameById',
	params: {id:234}
});

message_list[ <uuid> ] = callback;

** getting a response **

message.on('reply', function(msg){
	message_list[ msg.id ]( msg.data );
});

API

Usage from a web.js app:

query = mq.query 'User:getRecentTopics', id: 4
query.ok (name) ->
	mq.stream 
		channel: 'football:fantasy'
		data: name
	res.end 'success'
query.fail (err) ->
	res.end 'error'

Usage from within the data access layer:

db = require 'db'
zmq = require 'zeromq'

# require from models directory
require '../models/user'
require '../models/topic'

# receive zmq req
rep = zmq.createSocket 'rep'
rep.bind 'tcp://127.0.0.1:5555', (err) ->
	rep.on 'message', (_msg) ->
		msg = JSON.parse _msg
		
		# figure out the model and method
		mm = msg.method.split ':'
		model = mm[0]
		method = mm[1]
		
		# define the callback function
		callback = (data) ->
			msg.data = data
			rep.send JSON.stringify msg
			
		# send query to the database with callback
		query = db.model model
		query[ method ] msg.params, callback
		
		# gets deleted before the callback executes
		delete msg.method
		delete msg.params

Writing Models in the Data Access Layer

require.paths.unshift(process.cwd() + '/lib')
mongo = require 'mongoose'
redis = require 'redis'
db = require 'db'
async = require 'async'

class User

	getNameById: ( params, end ) ->
		console.log 'roflmaobbq'
		console.log 'sunny'
		end 'Sunnykit ' + params.id
		
	getTopicsFromUsers: ( params, end ) ->
		end ['t1', 't2', 't3']
		
	###
	COMMAND: User:getRecentTopics
	DESCRIPTION: Gets the most recent topics of users
	###
	getRecentTopics: ( params, end ) ->
		seq = async.seq
		seq.step ->
			db.model('User').getTopicsFromUsers {}, (topics) ->
				seq.topics = topics
				seq.next()
		seq.step ->
			seq.user = 'haha'
			seq.next()
		seq.last ->
			end
				topics: seq.topics
				user: seq.user
				
db.model 'User', User

Inside the 'db' helper

This file stores the models in memory to be accessed later

models = {}
exports.model = ( name, obj=null ) ->
	if obj?
		return models[ name ] = new obj
	models[ name ]