Step Eight: Finalizing Google App Engine (Backend) Logic

Now that we have a crash course in how we can leverage Google App Engine and understand what kind of request the Arduino will be making, we can finalize the App Engine code.

Using the two previous posts, we can assemble the final main.py using the blocks of logic from the previous post. The complete file looks like this (see previous posts additional comments):

	#!/usr/bin/env python
	import os
	import uuid
	import cgi
	from google.appengine.ext.webapp import template
	from google.appengine.ext import webapp
	from google.appengine.ext.webapp import util
	from google.appengine.ext import db
	import datetime
	import time
	class WeatherEntry(db.Model):
	date = db.DateTimeProperty(auto_now_add=True)
	temperature = db.FloatProperty()
	humidity = db.FloatProperty()
	other = db.FloatProperty()
	class DailyWeatherEntry(db.Model):
	date = db.IntegerProperty()
	temp_entry = db.TextProperty()
	humidity_entry = db.TextProperty()
	class MainHandler(webapp.RequestHandler):
	def get(self):
	self.redirect('http://apartmentarduino.blogspot.com/')
	class Weather(webapp.RequestHandler):
	def get(self):
	temp = str(float(cgi.escape(self.request.get('t')))/100)
	humidity = str(float(cgi.escape(self.request.get('h')))/100)
	strS = str(cgi.escape(self.request.get('s')))
	if strS == 'my_secret': #secret added since I don't want just anyone to pollute my weather data!
	rightNow = int(time.time())
	dayAgo = rightNow-86400
	recent_record = DailyWeatherEntry.gql("WHERE date > :1 ORDER BY date DESC",dayAgo)
	rightNow = str(rightNow)
	if recent_record.count()!=0: #update entry
	dayObj = recent_record[0]
	dayObj.temp_entry = dayObj.temp_entry + '['+rightNow+','+temp+'],'
	dayObj.humidity_entry = dayObj.humidity_entry + '['+rightNow+','+humidity+'],'
	dayObj.put()
	else: #create entry
	newEntry = DailyWeatherEntry(
	date = int(time.time()),
	temp_entry = '['+rightNow+','+temp+'],',
	humidity_entry = '['+rightNow+','+humidity+'],'
	)
	newEntry.put()
	self.response.headers.add_header("X-Arduino-Data", temp +','+ humidity )
	else:
	self.error(500)
	class ShowWeather(webapp.RequestHandler):
	def get(self):
	the_weather = db.GqlQuery(
	"SELECT * FROM DailyWeatherEntry ORDER BY date DESC LIMIT 1")
	template_values = {
	'weather' : the_weather
	}
	path = os.path.join(os.path.dirname(__file__), 'weather.html')
	self.response.out.write(template.render(path, template_values))
	def main():
	application = webapp.WSGIApplication([('/', MainHandler),
	('/weather/.?',Weather),
	('/w',ShowWeather)],
	debug=False)
	util.run_wsgi_app(application)
	if __name__ == '__main__':
	main()

view raw main.py hosted with ❤ by GitHub

Hopefully you have some understanding of the Django-like templating engine App Engine supports. There is an excellent hello-world tutorial in Google's official docs.

Next we'll visualize the data using a javascript based graphing library Flot!