CODEWITHSUNDEEP
pythonpostgresqlsqlalchemyflask
Kane Blueriver
Kane Blueriver

Reputation: 4268

Strange AttributeError in Flask based website

I am developing a website based on Flask and SQLAlchemy

  1. ssis created by sessionmaker in sqlalchemy.orm

  2. Anime, ActorQuote, AnimeComment are models based on database structure

```

@app.route('/page/<anime_name>', methods=['GET', 'POST'])
def show_page(anime_name):
    if request.method == 'GET':
        anime = ss.query(Anime).filter_by(anime_name=anime_name).first()
        actor_quotes = ss.query(ActorQuote).filter_by(anime_id=anime.id).all()
        anime_comments = ss.query(AnimeComment).filter_by(anime_id=anime.id).all()
        return render_template('page.html', anime=anime, actor_lines=actor_quotes, comments=anime_comments)

As excepted, it would return a page with these arguments -- anime, actor_quotes, anime_comments, and it does, but also throw a Attribute Error.

```

Traceback (most recent call last):
  File "/Library/Python/2.7/site-packages/flask/app.py", line 1836, in __call__
    return self.wsgi_app(environ, start_response)
  File "/Library/Python/2.7/site-packages/flask/app.py", line 1820, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "/Library/Python/2.7/site-packages/flask/app.py", line 1403, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/Library/Python/2.7/site-packages/flask/app.py", line 1817, in wsgi_app
    response = self.full_dispatch_request()
  File "/Library/Python/2.7/site-packages/flask/app.py", line 1477, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/Library/Python/2.7/site-packages/flask/app.py", line 1381, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/Library/Python/2.7/site-packages/flask/app.py", line 1475, in full_dispatch_request
    rv = self.dispatch_request()
  File "/Library/Python/2.7/site-packages/flask/app.py", line 1461, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/Users/windrunner/hiacg/index.py", line 138, in show_page
    actor_lines = ss.query(ActorQuote).filter_by(anime_id=anime.id).all()
AttributeError: 'NoneType' object has no attribute 'id'

When I use try-except to catch the error, it throws another UnboundLocalError.

```

try:
    anime = ss.query(Anime).filter_by(anime_name=anime_name).first()
    actor_quotes = ss.query(ActorQuote).filter_by(anime_id=anime.id).all()
    anime_comments = ss.query(AnimeComment).filter_by(anime_id=anime.id).all()
except AttibuteError:
    print 'AttibuteError occurs again!'

What is more strange is the website still works well as nothing happened.

  1. /page/化物语 This shows the page as expected without error.

  2. /page/剑风传奇 This shows the page as expected but with error.

Upvotes: 0

Views: 237

Answers (1)

Paolo Casciello
Paolo Casciello

Reputation: 8202

In your line

anime = ss.query(Anime).filter_by(anime_name=anime_name).first()

the variable anime is None if not found (as you said in database empty) and thus the AttributeError when trying to access None.id.

Btw I kindly suggest you to use Flask-SQLAlchemy extension that tackles all the db connection logic and exposes some useful functions such as `.first_or_404'. With it your code would become

anime = Anime.query.filter_by(anime_name=anime_name).first_or_404()

Upvotes: 3

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