Q: How to query GAE datastore to render a template (newbie level) I'm new to programming and I'm trying to grasp the concept of the GAE datastore. I'm trying to build an app to make it easy write contracts (http://contractpy.appspot.com). In the moment, I'm passing all the values I need to render the contract template from URL, this way: 
self.redirect('/your_contract?person=%s&nacionality=%s&profession=%s&maritalStatus=%s&SSN=%s&driverLicense=%s&email=%s&witness=%s&owner=%s&contractType=%s&address=%s' % (person_name, user_nacionality, user_profession, user_maritalStatus, user_SSN, user_driverLicense, user_email,
#witness, owner, contractType, address))

But doing so, it remains limited to one person (and, in the future, I'll need to render several persons data in the same contract).
Instead of doing that, I'd like to use GAE datastore query to fill the variable values of the template "your_contract.html". 
I know it's a simple question, but GAE datastore is completely obscure to me (I didn't grasp yet "the zen of the datastore", but I understand a little of SQL) and I'm learning OOProgramming just now. I read this article and I'v tried to follow this sample (Google guess_booK sample), but they were not enough for this brain. So, what is the best way to do this query, to render several persons data in one template? (Class Person is in the code bellow)
I was thinking this way: pass through URL a list with one data of each person (ex: Driver's License number):
self.redirect('/your_contract?driverLicense=%s' % (driverLicenseList))

And, in the handler "your_contract", use the value of "diverLicenseList" (after interact the list) to query GAE datastore, like this:
x = self.request.get('SSN')
contractingParty = db.GqlQuery("SELECT FROM Person WHERE SSN IS x")

Is this the right path?
Thanks in advance for any help!
My original code (before doing GAE query) is here:
# -*- coding: utf-8 -*-
# -*- coding: utf-8 -*-
#!/usr/bin/env python
#
# Copyright 2007 Google Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

import os

import webapp2

import jinja2

jinja_environment = jinja2.Environment(autoescape=True,
    loader=jinja2.FileSystemLoader(os.path.join(os.path.dirname(__file__), 'templates')))

import re

from google.appengine.ext import db

USER_RE = re.compile(r"^[a-zA-Z0-9_ -]{3,20}$")
def valid_person(person):
    return USER_RE.match(person)

PASS_RE = re.compile(r"^.{3,20}$")
def valid_SSN(SSN):
    return PASS_RE.match(SSN)

EMAIL_RE = re.compile(r"^[\S]+@[\S]+\.[\S]+$")
def valid_email(email):
    return EMAIL_RE.match(email)

import time

import datetime

def dateToday():
    today = datetime.datetime.today()
    todayDay = str(today.day)
    todayMonth = str(today.month)
    monthExt = {'1':' January ', '2':'February', '3':' March ', '4':'April', '5':'May', '6':'June', '7':' July ', '8':'August', '9':'September', '10':'October', '11':'November ', '12':'December'}
    todayYear = str(today.year)
    return(todayDay + ' of  ' + monthExt[todayMonth] + ' of ' + todayYear)

class MainHandler(webapp2.RequestHandler):
    def get(self):
        template_values = {"person": "",
                                       "SSN": "",
                                       "driverLicense": "",
                                       "email":"",
                                       "person_error": "",
                                       "SSN_error": "",
                                       "driverLicense_error": "",
                                       "address": "",
                                       "email_error": ""}
        template = jinja_environment.get_template('index.html')
        self.response.out.write(template.render(template_values))

    def post(self):
        person_name = self.request.get("person")
        user_nacionality = self.request.get('nacionality')
        user_profession = self.request.get('profession')
        user_maritalStatus = self.request.get('maritalStatus')
        user_SSN = self.request.get('SSN')
        user_email = self.request.get('email')
        user_driverLicense = self.request.get('driverLicense')
        person_error = ""
        SSN_error = ""
        driverLicense_error = ""
        geted_email_error = ""
        address = self.request.get('address')
        contractType = self.request.get("contractType")
        owner = self.request.get("owner")
        witness = self.request.get("witness")

        if (person_name and valid_person(person_name)) and (user_SSN and valid_SSN(user_SSN)) and ((not user_email) or (user_email and valid_email(user_email))):
            a = People(firstName = person_name,
                                   nacionality = user_nacionality,
                                   maritalStatus = user_maritalStatus,
                                   profession = user_profession,
                                   SSN = int(user_SSN),
                                   driverLicense = int(user_driverLicense)
                                   #address = user_address
                                   )
            a.put()
            self.redirect('/your_contract?person=%s&nacionality=%s&profession=%s&maritalStatus=%s&SSN=%s&driverLicense=%s&email=%s&witness=%s&owner=%s&contractType=%s&address=%s' % (person_name, user_nacionality, user_profession, user_maritalStatus, user_SSN, user_driverLicense, user_email,
witness, owner, contractType, address))

        else:
            if not person_name or not valid_person(person_name):
                person_error = "Oh no!!! this person name isn't valid!"
            if not user_SSN or not valid_SSN(user_SSN):
                SSN_error = "Oh no!!! SSN isn't valid!"
            if user_email and not valid_email(user_email):
                geted_email_error = "Oh no!!! e-mail isn't valid!"
            template_values = {"person": person_name,
                                "nacionality": user_nacionality,
                                "maritalStatus": user_maritalStatus,
                                "profession": user_profession,
                                "SSN": user_SSN,
                                "driverLicense": user_driverLicense,
                                "email": user_email,
                                "person_error": person_error,
                                "SSN_error": SSN_error,
                                "driverLicense_error": user_driverLicense,
                                "address": address,
                                "email_error": geted_email_error}
            template = jinja_environment.get_template('index.html')
            self.response.out.write(template.render(template_values))

class your_contractHandler(webapp2.RequestHandler):
    def get(self):
        geted_person_name = self.request.get('person')
        geted_user_nacionality = self.request.get("nacionality")
        geted_user_profession = self.request.get("profession")
        geted_user_maritalStatus = self.request.get("maritalStatus")
        geted_user_SSN = self.request.get('SSN')
        geted_user_email = self.request.get('email')
        geted_user_driverLicense = self.request.get('driverLicense')
        geted_person_error = ""
        geted_SSN_error = ""
        geted_driverLicense_error = ""
        geted_address = self.request.get('address')
        geted_owner = self.request.get("owner")
        geted_witness = self.request.get("witness")
        geted_contractType = self.request.get("contractType")
        geted_dateToday = dateToday()
        your_contract = jinja_environment.get_template('your_contract.html')
        your_contract_values = {"person":geted_person_name,
                                "nacionality":geted_user_nacionality,
                                "maritalStatus": geted_user_maritalStatus,
                                "profession": geted_user_profession,
                                "SSN":geted_user_SSN,
                                "driverLicense":geted_user_driverLicense,
                                "address":geted_address,
                                "email":geted_user_email,
                                "contractType":geted_contractType,
                                "dateContract":geted_dateToday,
                                }
        template = jinja_environment.get_template('index.html')
        self.response.out.write(your_contract.render(your_contract_values))

class People(db.Model):
    name = db.StringProperty(required = True)
    nacionality = db.StringProperty(required = True)
    maritalStatus = db.StringProperty(required = True)
    profession = db.StringProperty(required = True)
    SSN = db.IntegerProperty(required = True)
    driverLicense = db.IntegerProperty(required = True)
#    address = db.PostalAdressProperty(required = True)
#    condition = db.StringProperty(required = False, choices=set(["buyer", "seller", "renter", "owner", "witness"]))

##class Acts(db.Model):
##    firstPart = db.StringProperty(required = True)
##    secondPart = db.StringProperty(required = True)
##    contractNumber = db.IntegerProperty(required = False)
##    contractDate = db.DateProperty(auto_now_add=True)
##    contractDraft = db.TextProperty(required = True)


app = webapp2.WSGIApplication([('/', MainHandler), ('/your_contract', your_contractHandler)],
                              debug=True)


A: There are several issues in your code, starting with the design.
You should have two classes that are getting stored in the datastore (Contract and Person)
  (If you were using NDB you could have a contract with a structured Property for the Person, but we'll stay simple.)
The Contract could have whatever things you need for a contract and then have a 
people = ListProperty(db.Key)
After you put() a model instance the db.key() will be populated with the key. That's what you should be passing around to other parts of your code and storing in the ListProperty above.
For example in your redirect after the POST you would have something like 
self.redirect('/your_contract?person=%s' % a.key()')
To load the stored person you would do:
person = db.get(self.request.get('person'))
If you are passing multiple person keys you'll have to double check the webob documentation on how to read multiple values with same key in querystring, but I know it comes back as a list.
Hope this helps
