CODEWITHSUNDEEP
google-app-engine
Anton Danilchenko
Anton Danilchenko

Reputation:

Google App Engine, How to automatically load model class for ReferenceProperty

I have modular project structure, like this:

./main.py
./app.yaml
../articles
.../__init__.py
.../models.py
../blog
.../__init__.py
.../models.py
../comments
.../__init__.py
.../models.py

I have defined models in file models.py for each package (this is application). I have defined next models for "comments" application:

class Comment(db.Model):
    author      = db.UserProperty(auto_current_user_add=True)
    title       = db.StringProperty(default="Title")
    text        = db.TextProperty("Message", default="Your message")
    # references to any model
    object      = db.ReferenceProperty()

and in "articles" application I have defined next models:

class Article(db.Model):
    author      = db.UserProperty(auto_current_user_add=True)
    title       = db.StringProperty(default="Title")
    text        = db.TextProperty("Message", default="Your message")

1) On first loading of page - I create new article:

from articles.models import Article
article = Article(title="First article", text="This is first article")
article.put()

2) On second loading of page I create new comment:

from articles.models import Article
from comments.models import Comment
article = Article.get_by_id(1)
comment = Comment(title="First comment", text="This is first comment")
comment.put()

3) On thind loading of page, I want to see all comments for all articles, blogs, and other objects in whole datastore:

from comments.models import Comment
comments = Commen.all()
for comment in comments:
    # print comment and article title
    print "%s: %s" % (comment.title, comment.object.title)

Actual result: "KindError: No implementation for kind 'Article'"

Expected result: automatically detect object type for reference and load this class

See more on: http://code.google.com/p/appengine-framework/issues/detail?id=17
Project need your help!

Upvotes: 1

Views: 433

Answers (2)

Anton Danilchenko
Anton Danilchenko

Reputation:

In my project GAE framework I have solve this issue. On the first page loading I have load all models in memory.

What if we have models with the same name, for example Comment model in "blog" and "board" applications? In this case we have automatically add prefix for models for the King of this model. In result we have the different names for models in different applications: BlogComment and BoardComment.

You can learn more in source code to understand how we do this implementation.

Upvotes: 0

Nick Johnson
Nick Johnson

Reputation: 101149

In order to be able to return entities of a given kind, App Engine has to be able to find the Model class for it. There's no mechanism built in for doing so, because all it has to look it up with is the entity kind, which can be any arbitrary string.

Instead, import the modules containing the models you may reference from the module containing the Comment model. That way, any time you can perform a query on Comment, all the relevant models are already loaded.

Upvotes: 1

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