Search 2 tables simultaneously using flask-executor - flask

Question

I have 2 large postgres tables which have an index so that I can perform a full text search on each.
Typically, they look like:
class Post_1(db.Model):
query_class = PostQuery
id = db.Column(db.Integer, primary_key=True)
title = db.Column(db.String)
content = db.Column(db.Text)
datestamp = db.Column(db.Float)
search_vector = db.Column(TSVectorType('title', 'content'))
and
class Post_2(db.Model):
query_class = PostQuery
id = db.Column(db.Integer, primary_key=True)
title = db.Column(db.String)
content = db.Column(db.Text)
datestamp = db.Column(db.Float)
search_vector = db.Column(TSVectorType('title', 'content'))
In my flask application, to get the documents which have a specific keyword in one of the tables, I would do:
Post_1.query.search(keyword).\
order_by(Post_1.datestamp.desc()).limit(1)
Since I want to run the same search simultaneously on both tables, I wanted to use flask-executor and wrote the following code:
from flask_executor import Executor
executor = Executor(app)
futures=[]
keyword = "covid"
future=executor.submit(Post_1.query.search(keyword).\
order_by(Post_1.datestamp.desc()).limit(1))
futures.append(future)
future = executor.submit(Post_2.query.search(keyword).\
order_by(Post_2.datestamp.desc()).limit(1))
futures.append(future)
This does not work and I get the following error:
RuntimeError: This decorator can only be used at local scopes when a request context is on the stack. For instance within view functions.
Could anyone help me please?

Answer 1

The error you're getting is because flask-executor is intended to run tasks inside view functions - that is, as part of a request from a user. You're running your code outside of a view (i.e. outside of a scope that would normally be in place when your user is interacting with your application).
Do you need to do this, or is this simply part of a test? If you do something like this, just to test it out:
#app.route('/test')
def testroute():
future=executor.submit(Post_1.query.search(keyword).\
order_by(Post_1.datestamp.desc()).limit(1))
futures.append(future)
future = executor.submit(Post_2.query.search(keyword).\
order_by(Post_2.datestamp.desc()).limit(1))
futures.append(future)
Then you should no longer get the error about running outside of a request context, because the code will be running as part of a request (i.e. inside a view function).
As a side note, the SQLAlchemy tasks you're submitting aren't callable - they're not function objects. Executors, whether the one created by Flask-Executor or the vanilla ones you can get via concurrent.futures, expect you to pass a "callable". I suspect your code still wouldn't work unless it was something like:
query = Post_1.query.search(keyword).\
order_by(Post_1.datestamp.desc()).limit(1).all
future = executor.submit(query)
Notice the lack of brackets at the end, because I want to use the callable object itself, not the result it will return
The executor would then "call" the object that had been passed:
executor.submit(Post_1.query.search(keyword).\
order_by(Post_1.datestamp.desc()).limit(1).all()