peewee.OperationalError：在“ AS”附近：语法错误

Question

So I don't quite understand what exactly the problem here is. I'm working with python-flask and currently trying to call certain posts from my Post model. However, I always get this "peewee.OperationalError: near "AS": syntax error" error message which is caused by the following class method in my User model:

    @classmethod 
    def get_stream(self):
        return Post.select().where(Post.user == self)

I call this method in the following route to define stream, which is then passed to the template:

@app.route('/stream')
@app.route('/stream/<username>')
def stream(username=None):
    template = 'stream.html'
    if username and username != current_user.username:
        user = social.User.select().where(social.User.username**username).get()
        stream = user.posts.limit(100)
    else:
        stream = current_user.get_stream().limit(100)
        user = current_user
    if username:
        template = "user_stream.html"
#   stream = social.Post.select().where(social.Post.user == current_user.id)
    return render_template(template, stream=stream, user=user)

Using the line that is currently commented it works just fine, but without it I get the error. So it is for sure a problem

Anyone an idea what the issue is?

For reference, here are the User and Post models:

class User(UserMixin, Model):
    username = CharField(unique=True)
    email = CharField(unique=True)
    password = CharField(max_length=100)
    joined_at = DateTimeField(default=datetime.datetime.now)
    is_admin = BooleanField(default=False)

    class Meta:
        database = USER_DB
        order_by = ('joined_at',)

    @classmethod 
    def get_stream(self):
        return Post.select().where(Post.user == self)

    @classmethod
    def create_user(cls, username, email, password, admin=False):
        try:
            with USER_DB.transaction():
                cls.create(
                    username=username,
                    email=email,
                    password=generate_password_hash(password),
                    is_admin=admin)
        except IntegrityError:
            raise ValueError("User already exists.")


class Post(Model):
    timestamp = DateTimeField(default=datetime.datetime.now)
    user = ForeignKeyField(
        rel_model=User,
        related_name='posts'
        )
    content = TextField()

    class Meta:
        database = USER_DB
        order_by = ('-timestamp',)

Traceback (most recent call last)

File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/flask/app.py", line 1836, in __call__
return self.wsgi_app(environ, start_response)
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/flask/app.py", line 1820, in wsgi_app
response = self.make_response(self.handle_exception(e))
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/flask/app.py", line 1403, in handle_exception
reraise(exc_type, exc_value, tb)
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/flask/_compat.py", line 33, in reraise
raise value
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/flask/app.py", line 1817, in wsgi_app
response = self.full_dispatch_request()
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/flask/app.py", line 1477, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/flask/app.py", line 1381, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/flask/_compat.py", line 33, in reraise
raise value
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/flask/app.py", line 1475, in full_dispatch_request
rv = self.dispatch_request()
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/flask/app.py", line 1461, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/Users/SuperMario/Desktop/treehouse/flask_track/simple_app.py", line 49, in stream
return render_template(template, stream=stream, user=user)
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/flask/templating.py", line 128, in render_template
context, ctx.app)
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/flask/templating.py", line 110, in _render
rv = template.render(context)
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/jinja2/environment.py", line 989, in render
return self.environment.handle_exception(exc_info, True)
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/jinja2/environment.py", line 754, in handle_exception
reraise(exc_type, exc_value, tb)
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/jinja2/_compat.py", line 37, in reraise
raise value.with_traceback(tb)
File "/Users/SuperMario/Desktop/treehouse/flask_track/templates/user_stream.html", line 1, in top-level template code
{% extends "stream.html" %}
File "/Users/SuperMario/Desktop/treehouse/flask_track/templates/stream.html", line 1, in top-level template code
{% extends "layout.html" %}
File "/Users/SuperMario/Desktop/treehouse/flask_track/templates/layout.html", line 25, in top-level template code
{% block content %}     {% endblock %}
File "/Users/SuperMario/Desktop/treehouse/flask_track/templates/user_stream.html", line 26, in block "content"
{{ super() }}
File "/Users/SuperMario/Desktop/treehouse/flask_track/templates/stream.html", line 5, in block "content"
{% for post in stream %}
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/peewee.py", line 2866, in __iter__
return iter(self.execute())
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/peewee.py", line 2859, in execute
self._qr = ResultWrapper(model_class, self._execute(), query_meta)
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/peewee.py", line 2555, in _execute
return self.database.execute_sql(sql, params, self.require_commit)
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/peewee.py", line 3366, in execute_sql
Open an interactive python shell in this frameself.commit()
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/peewee.py", line 3212, in __exit__
reraise(new_type, new_type(*exc_args), traceback)
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/peewee.py", line 125, in reraise
raise value.with_traceback(tb)
File "/Users/SuperMario/Desktop/treehouse/treehouse_flask_track/lib/python3.4/site-packages/peewee.py", line 3359, in execute_sql
cursor.execute(sql, params or ())

Answer 1

Decorating a method with @classmethod tells Python to pass the class rather than the instance as the first argument. Typically, you name the first argument cls in that case to keep things clear.

Your method is trying to get all Post s with the user instance it's called from, but instead calling that method passes the User class. Remove the @classmethod decorator.

def get_stream(self):
    return Post.select().where(Post.user == self)

Now self is a user instance, and the relation Post.user == self makes sense.

Answer 2

The @classmethod before defining the method in my User model prevented it from working. I still have to figure out why, but for now it works.