Dynamic URL's inside Google's AppEngine

Question

Good Afternoon,

I'm currently trying to build something incredibly simple inside of the Google AppEngine. The goal is to build a simple photo sharing application that will connect back to my iPhone application. It's all a learning experience for both Python and Objective-C.

(I've been a PHP programmer for quite some time).

The goal, create URL's that look like the following: /img/{{ model.key.id }}

The problem is that it seems no matter how I do the python script, I either end up with an error or simply get nothing to display on my template page that's wrapped in the FOR statement.

My App.yaml File:

application: randomwebappname
version: 1
runtime: python
api_version: 1

handlers:
- url: /media
  static_dir: media

- url: /b/.*
  script: beta.py
  login: required

- url: /.*
  script: main.py

My Model (inside beta.py):

class Photo(db.Model):
    author = db.StringProperty()
    title = db.StringProperty()
    slugline = db.StringProperty()
    content = db.StringProperty(multiline=True)
    coordinates = db.StringProperty()
    avatar = db.BlobProperty()
    date = db.DateTimeProperty(auto_now_add=True)

My Class For Viewing The Image Page:

class ViewPage(webapp.RequestHandler):
def get(self, id):


template_values = {
    'image': image,
}

path = os.path.join(os.path.dirname(__file__), 'templates/view.html')
self.response.out.write(template.render(path, template_values))

I tried all of the following in my class, but they all end in failure. I tried them with key, key.name, and key.id in the URL:

photos = db.Query(Photo).filter('key', slug).fetch(limit=1)

photos = Photo.get_by_key_name(id)

photos = Photo.get_by_key_name(key)

key = db.Key.from_path('Photo', id) 

photos = db.GqlQuery("SELECT * FROM Photo WHERE __key__ = :key", key=key)

photos = db.get(photo_key)

photos = self.request.get("id")

My URL's:

application = webapp.WSGIApplication([
    ('/b/', HomePage),
    ('/b/upload', UploadPage),
    ('/b/add', MainPage),
    ('/b/img', Image),
    ('/b/img/([-\w]+)', ViewPage),
    ('/b/submit', Submission)
], debug=True)

The Template Query:

{% for photo in photos %}
<img alt="" title="" src="img?img_id={{ photo.key }}" alt="main image" />
{% endfor %}

This seems like it would be something incredibly simple and I know I'm missing something, but I'm just not sure where it's at. I would write this in PHP, but I like the concept of AppEngine and I've said above, it's a good Python learning experience.

As a side note, this application does work on the homepage of the site. I simply have a GQL query and it outputs the images fine, it just fails when I try to go to the /img/id pages.

Any advice guys (and gals)? Thanks in advance!

UPDATE #1:
As per Jonathan's request, the following is the Image class:

class Image (webapp.RequestHandler):
    def get(self):
        photo = db.get(self.request.get("img_id"))
        if photo.avatar:
            self.response.headers['Content-Type'] = "image/png"
            self.response.out.write(photo.avatar)
        else:
            self.response.out.write("No image")

Also, after posting this, I realized that this was part of the problem as I was trying to do /img as the actual image and /img/ to display the view page. I've since changed this and now have a working model. But it's based upon the Key and not key.id:

URL:

('/b/i', ViewPage)

New ViewPage Class:

class ViewPage(webapp.RequestHandler):
    def get(self):
    image = db.get(self.request.get("id"))  

    template_values = {
        'image': image,
    }

    path = os.path.join(os.path.dirname(__file__), 'templates/view.html')
    self.response.out.write(template.render(path, template_values))

So... to get to the View page (which includes comments and such), you now have to go to the following URL: /b/i?img_id={{ image.key }}

Atleast the page is working now, but I would much prefer to get the page to look like the following as stated above: /b/img/{{ image.key.id }}

Update #2: ViewPage class updated as well as URL's:

class ViewPageV2(webapp.RequestHandler):
    def get(self, id):
    images = [ db.get(id) ]

    template_values = {
        'image': image,
    }

    path = os.path.join(os.path.dirname(__file__), 'templates/view.html')
    self.response.out.write(template.render(path, template_values))

New URL: ('/b/image/([-\w]+)', ViewPageV2),

The following are two screenshots with one being proof of id "1" existing and the error that is coming with it currently.

alt text http://img215.imageshack.us/img215/9123/screenshot20091130at937.png

alt text http://img215.imageshack.us/img215/2207/screenshot20091130at938.png

Again, Thanks All!

Answer 1

A simple way to grab them all:

photos = Photo.gql('ORDER BY __key__')

For more, see Queries on Keys in the App Engine docs.

Are you storing your photos with predefined keys?

photo = Photo(key_name="xzy123")
photo.put()

Then you can retrieve it in your ViewPage:

photos = [ Photo(key_name="%s" % id) ]

See Getting an Entity Using a Key.

Finally, to retrieve a photo based on its appengine-assigned key and assuming this key is present in the URL (e.g., http://host/b/img/ahByY..., so change your template to generate URLs of this form), use

class ViewPage(webapp.RequestHandler):
  def get(self, id):
    photos = [ db.get(id) ]
    ...