TypeError: 'MongoEngine' object is not subscriptable

Question

In a flask application I'm using MongoEngine as a ORM. I'm defining the db object in my main python file and I'm trying to re-use it from different classes by importing it from there.

This is how I create db in my main py file:

db = MongoEngine(app, config={
    'db': "MY_DB",
    'host': "myhost",
    'port': 27017,
    'username': 'user',
    'password': 'password'
})

This is what I'm trying to do from another class (whose instance is being used from a rest entry point):

from app.engine import db

class ReportService:
    def __init__(self):
        pass

    @staticmethod
    def download_raw_data(collection_name, _from, _to):
        logger.info('Downloading raw_data from collection: ' + collection_name)

        query = {
            "date": {"$gte": _from, "$lte": _to}
        }

        result = db[collection_name].find(query)

        return result

However I'm getting this error when calling that entry point:

[2019-02-21 10:52:22 +0000] [12] [ERROR] Error handling request module/download/rawdata
Traceback (most recent call last):
  File "/app/env/lib/python3.6/site-packages/gunicorn/workers/base_async.py", line 56, in handle
    self.handle_request(listener_name, req, client, addr)
  File "/app/env/lib/python3.6/site-packages/gunicorn/workers/base_async.py", line 107, in handle_request
    respiter = self.wsgi(environ, resp.start_response)
  File "/app/env/lib/python3.6/site-packages/flask/app.py", line 2309, in __call__
    return self.wsgi_app(environ, start_response)
  File "/app/env/lib/python3.6/site-packages/flask_socketio/__init__.py", line 43, in __call__
    start_response)
  File "/app/env/lib/python3.6/site-packages/engineio/middleware.py", line 67, in __call__
    return self.wsgi_app(environ, start_response)
  File "/app/env/lib/python3.6/site-packages/flask/app.py", line 2295, in wsgi_app
    response = self.handle_exception(e)
  File "/app/env/lib/python3.6/site-packages/flask_cors/extension.py", line 161, in wrapped_function
    return cors_after_request(app.make_response(f(*args, **kwargs)))
  File "/app/env/lib/python3.6/site-packages/flask/app.py", line 1741, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/app/env/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise
    raise value
  File "/app/env/lib/python3.6/site-packages/flask/app.py", line 2292, in wsgi_app
    response = self.full_dispatch_request()
  File "/app/env/lib/python3.6/site-packages/flask/app.py", line 1815, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/app/env/lib/python3.6/site-packages/flask_cors/extension.py", line 161, in wrapped_function
    return cors_after_request(app.make_response(f(*args, **kwargs)))
  File "/app/env/lib/python3.6/site-packages/flask/app.py", line 1718, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/app/env/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise
    raise value
  File "/app/env/lib/python3.6/site-packages/flask/app.py", line 1813, in full_dispatch_request
    rv = self.dispatch_request()
  File "/app/env/lib/python3.6/site-packages/flask/app.py", line 1799, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/app/controllers/modules.py", line 51, in download_raw_data
    result = reports.download_raw_data(collection_name, start_time, end_time)
  File "/app/service/services.py", line 114, in download_raw_data
    result = db[collection_name].find(query)
TypeError: 'MongoEngine' object is not subscriptable

What am I doing wrong? I also would like to understand why is this error taking place.

Thanks in advance

bagerard · Accepted Answer · 2021-02-24 10:55:10Z

2

What's returned by Mongoengine(...) is not immediately a pymongo database instance, you have to use get_db() if you want it:

me = MongoEngine(app, config={...})
...
db = me.get_db()
db[collection_name].find(query)

I agree that the docs is confusing as it calls it db which is misleading...

edited Feb 24, 2021 at 10:55

answered Jun 4, 2019 at 19:22

bagerard

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