SqlAlchemy Query.All() Unexpectedly Returning OperationalError - flask

Question

I'm implementing search functionality using Elasticsearch in a "Reddit clone" web application that I'm developing. I want to support searching for threads, users, and subreddits, but when I enter a search query and search for one of the 3 above mentioned categories that does not hold any matches, I'm getting an unexpected "OperationalError" instead of an empty set of results.
As shown in the code I included, I attempted to use the sqlalchemy.orm.query.Query.all() function which returned the following error:
OperationalError: (sqlite3.OperationalError) near "END": syntax error
[SQL: SELECT user.id AS user_id, user.username AS user_username, user.email AS user_email, user.password_hash AS user_password_hash, user.last_sign_in AS user_last_sign_in
FROM user
WHERE 1 != 1 ORDER BY CASE user.id END]
(Background on this error at: http://sqlalche.me/e/e3q8)
I researched other StackOverflow posts and found that the first() function internally processes the database result and returns None if no results are found, but when I switched to that function, I faced this error:
OperationalError: (sqlite3.OperationalError) near "END": syntax error
[SQL: SELECT user.id AS user_id, user.username AS user_username, user.email AS user_email, user.password_hash AS user_password_hash, user.last_sign_in AS user_last_sign_in
FROM user
WHERE 1 != 1 ORDER BY CASE user.id END
LIMIT ? OFFSET ?]
[parameters: (1, 0)]
(Background on this error at: http://sqlalche.me/e/e3q8)
Checking the documentation for SqlAlchemy, I don't see any mention of this error in either function, and reading the meaning of OperationalError, I'm concerned that my database setup is possibly incorrect.
app/routes.py: This is the route that handles search requests made to the following URL: http://localhost:5000/search?q=&index=
#app.route('/search', methods=['GET'])
def search():
print 'Hit the /search route!'
if not g.search_form.validate():
return redirect(url_for('index'))
page = request.args.get('page', 1, type=int)
target_index = request.args.get('index', 'thread')
if target_index == 'thread':
results, total = Thread.search(g.search_form.q.data, page, app.config['POSTS_PER_PAGE'])
print 'Called Thread.search(), total results = {}'.format(total['value'])
elif target_index == 'user':
results, total = User.search(g.search_form.q.data, page, app.config['POSTS_PER_PAGE'])
print 'Called User.search(), total results = {}'.format(total['value'])
elif target_index == 'subreddit':
results, total = Subreddit.search(g.search_form.q.data, page, app.config['POSTS_PER_PAGE'])
print 'Called Subreddit.search(), total results = {}'.format(total['value'])
else:
return render_template('404.html')
try:
results = results.all()
except OperationalError:
results = [None]
total = total['value']
next_url = url_for('search', index=target_index, q=g.search_form.q.data, page=page + 1) if total > page * app.config['POSTS_PER_PAGE'] else None
prev_url = url_for('search', index=target_index, q=g.search_form.q.data, page=page - 1) if page > 1 else None
results_list = zip(results, [None] * len(results)) # Temporarily to match expected input for template
return render_template('search.html', title=_('Search'), results_list=results_list, next_url=next_url, prev_url=prev_url, query=g.search_form.q.data, index=target_index)
app/models.py:
class SearchableMixin(object):
#classmethod
def search(cls, expression, page, per_page):
ids, total = query_index(cls.__tablename__, expression, page, per_page)
if total == 0:
return cls.query.filter_by(id=0), 0
when = []
for i in range(len(ids)):
when.append((ids[i], i))
return cls.query.filter(cls.id.in_(ids)).order_by(
db.case(when, value=cls.id)), total
#classmethod
def before_commit(cls, session):
session._changes = {
'add': list(session.new),
'update': list(session.dirty),
'delete': list(session.deleted)
}
#classmethod
def after_commit(cls, session):
for obj in session._changes['add']:
if isinstance(obj, SearchableMixin):
add_to_index(obj.__tablename__, obj)
for obj in session._changes['update']:
if isinstance(obj, SearchableMixin):
add_to_index(obj.__tablename__, obj)
for obj in session._changes['delete']:
if isinstance(obj, SearchableMixin):
remove_from_index(obj.__tablename__, obj)
session._changes = None
#classmethod
def reindex(cls):
for obj in cls.query:
add_to_index(cls.__tablename__, obj)
db.event.listen(db.session, 'before_commit', SearchableMixin.before_commit)
db.event.listen(db.session, 'after_commit', SearchableMixin.after_commit)
# Below is one model that implements SearchableMixin to allow searching # for users. Thread and Subreddit models follow the same logic.
class User(db.Model, UserMixin, SearchableMixin):
__searchable__ = ['username']
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(64), index=True, unique=True)
# <Remaining User model fields here...>
app/search.py: (Holds the underlying search functions to query Elasticsearch indices)
def add_to_index(index, model):
if not app.elasticsearch:
return
payload = {}
for field in model.__searchable__:
payload[field] = getattr(model, field)
app.elasticsearch.index(index=index, doc_type=index, id=model.id,
body=payload)
def remove_from_index(index, model):
if not app.elasticsearch:
return
app.elasticsearch.delete(index=index, doc_type=index, id=model.id)
def query_index(index, query, page, per_page):
if not app.elasticsearch:
return [], 0
search = app.elasticsearch.search(
index=index,
body={'query': {'multi_match': {'query': query, 'fields': ['*']}},
'from': (page - 1) * per_page, 'size': per_page})
ids = [int(hit['_id']) for hit in search['hits']['hits']]
return ids, search['hits']['total']
As my included app/routes.py shows, I made a workaround by catching the OperationalError and treating it as an indicator that no results were found, but since the all() documentation makes no mention of it, I did not expect there to be this exception being raised.

Answer 1

I simplified the generated query a bit by hiding all fields you retrieve behind the asterisk.
SELECT user.*
FROM user
WHERE 1 != 1
ORDER BY CASE user.id END
First of all, this query will not return any values as long as 1 != 1 is a where clause, since that is false by definition. Is it possible ids is empty? That might also very much explain the ill-formatted CASE statement, which is the source of the error. Normally, case(dict(a=1, b=2), value=User.name) should result in CASE WHEN name = 'a' THEN 1 WHEN name = 'b' THEN 2 END, which would properly execute.