[Flask] Store Data in a SQLite-Database with Flask

[Anthony Ford]

I created a similar system to monitor a series of Modbus enabled GPIO units
(Acromag
<https://www.acromag.com/catalog/318/ethernet-modbus-profibus-io/ethernet-io-modules/multi-function-io/busworks-900en-series>
units).
Flask is not well suited  to having a data logger within it.

Flask is more of a User Interface, and is event based, meaning that nothing
happens until the server (and therefore your Flask app) get a request from
a browser. This means you can easily fetch the current state when someone
wants it (i.e. a big "FETCH STATUS" button). However, if you need periodic
monitoring (like I did), it is better to have a separate program that ONLY
does the data logging.

You can possibly get away with threading, and launching a separate thread
from within your Flask app, but I personally think it's not worth the
complexity.

If you use a full database system (PostgreSQL is my go-to) instead of
SQLite, it is easy to have the logger application dump into the database,
while the Flask app reads from the Database.

If you avoid using Flask-SQLAlchemy in favor of vanilla (or standard)
SQLAlchemy, you can even share the database modules between the apps (via a
common shared package, or just plain importing from one or the other).

If desired, I can talk more about my approach, but unfortunately I can't
share code, and sanitizing the code to be shareable would take a lot of
work.

Hope this helps!

Anthony Ford,
KF5IBN,
ford.anthonyj at gmail.com

On Sun, Nov 20, 2016 at 1:23 PM, Dmitry <d at ddipp.net> wrote:

> Hello Andreas!
>
> Tell me - why do you need a flask?
> Flask - web framework, and you have a function, framed by "@app.route" is
> caused not through the web, and from the same program.
> Try to remove the "@ app.route" to function.
> Also, you will not be initialized "g.db". Think about why.
>
> 20.11.2016 21:23, Andreas Dorfner пишет:
>
> Hello everyone,
>
> I'm new to python and flask web development.
> I have to realize a data logger using flask. By using another framework
> called 'pymodbus', I get some data from
> an energy meter and save that data to a variable called 'crv_data' (see
> file attached). This part is working so far!
>
> The second part of the project contains the storage of 'crv_data' to a
> SQLite-Database. For that, I'm using flask.
> For creating a table with five columns, a file 'schema.sql' (also
> attached) is included.
>
> If the file 'logger.py' is running, a database is produced with the
> desired layout and some data in 'crv_data' is available.
> But there is no data included in the database.
>
> I think there is an error in function 'add_entry()' (starting in line 72
> of logger.py file), because if I call the function
> in the infinite loop (line 103), the program stops running.
> Maybe I have to say that I using Beaglebone Black with running Debian on
> it.
>
> Does anybody have an idea, why the program doesn't work?
> Many thanks,
> Andreas
>
>
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