Google App Engine Datastore: Extracting data using GQL query

Question

I'm currently playing with the Google App Engine datastore, and trying to extract some data from my applications database using GQL.

import os
import re
import random
import hashlib
import hmac
from string import letters

import webapp2
import jinja2

from google.appengine.ext import db

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

class Handler(webapp2.RequestHandler):
    def write(self, *a, **kw):
        self.response.out.write(*a, **kw)
    def render_str(self, template, **params):
        t = jinja_env.get_template(template)
        return t.render(params)
    def render(self, template, **kw):
        self.write(self.render_str(template, **kw))

class Users(db.Model):
    name = db.StringProperty(required = True)
    password = db.StringProperty(required = True)
    email = db.EmailProperty(required = True)
    address = db.PostalAddressProperty(required = True)
    join_date = db.DateTimeProperty(auto_now_add = True)
    dob = db.DateTimeProperty()
    phone = db.PhoneNumberProperty()

class MainPage(Handler):
    def get(self):
        self.render("signup-form.html")
    def post(self):
        name = self.request.get("username")
        password = self.request.get("password")
        verify = self.request.get("verify")
        email = self.request.get("email")
        address = self.request.get("address")
        phone = self.request.get("phone")

        a = Users(name = name, password = password, email = email, address = address, phone = phone)
        a.put()
        p = Users.all()
        ans = p.filter("name = :1", "Manas")
        if(ans.email == "manas.oid@gmail.com"):
            self.response.write("Email found")
        else:
            self.response.write("Not found")


app = webapp2.WSGIApplication([('/', MainPage)], debug=True)

Now, there's already a 'Manas' attribute stored in my Users table, with 'manas.oid@gmail.com' as its corresponding email id. So, accordingly, I should get a 'Email found' message displayed. However, I get this error:

Traceback (most recent call last):
  File "C:\Program Files\Google\google_appengine\lib\webapp2-2.5.2\webapp2.py", line 1535, in __call__
    rv = self.handle_exception(request, response, e)
  File "C:\Program Files\Google\google_appengine\lib\webapp2-2.5.2\webapp2.py", line 1529, in __call__
    rv = self.router.dispatch(request, response)
  File "C:\Program Files\Google\google_appengine\lib\webapp2-2.5.2\webapp2.py", line 1278, in default_dispatcher
    return route.handler_adapter(request, response)
  File "C:\Program Files\Google\google_appengine\lib\webapp2-2.5.2\webapp2.py", line 1102, in __call__
    return handler.dispatch()
  File "C:\Program Files\Google\google_appengine\lib\webapp2-2.5.2\webapp2.py", line 572, in dispatch
    return self.handle_exception(e, self.app.debug)
  File "C:\Program Files\Google\google_appengine\lib\webapp2-2.5.2\webapp2.py", line 570, in dispatch
    return method(*args, **kwargs)
  File "F:\Python 2.7\engineapp1\HelloApp\appapp\main.py", line 48, in post
    ans = p.filter("name = :1", "Manas")
  File "C:\Program Files\Google\google_appengine\google\appengine\ext\db\__init__.py", line 2560, in filter
    prop = match.group(1)
AttributeError: 'NoneType' object has no attribute 'group'

What seems to be wrong with my query?

Answer 1

Query.filter does not accept a placeholder.

Replace following line:

ans = p.filter("name = :1", "Manas")

with:

ans = p.filter("name =", "Manas")

UPDATE

filter returns an iterable, not a single record. You need to iterate it to check whether given email exist:

for x in ans:
    if x.email == "manas.oid@gmail.com":
        self.response.write("Email found")
else:
    self.response.write("Not found")

More preferably, using chained Query.filter and Query.count, you don't need to iterate it.

ans = p.filter("name =", "Manas").filter("email =", "manas.oid@gmail.com")
if ans.count(limit=1):
    self.response.write("Email found")
else:
    self.response.write("Not found")