We’re setting Flask configs which the extension will in turn use to configure SQLAlchemy correctly. For this, we will use the variables from the environment and their values. We need to import it at the top of the file. To use it with Flask, there’s an extension to make them play together nicely. Get the data you need and also takes care of many more technical details. It make it possible to create the right tables, SQLAlchemy takes care of doing the database-busywork if We can define classes with data fields which we need, and get lists of those The module we’ll use to deal with data in databases is called SQLAlchemy. We use it to get all the vars we will need to access PostgreSQL. POSTGRES_DB = get_env_variable("POSTGRES_DB") POSTGRES_PW = get_env_variable("POSTGRES_PW") POSTGRES_USER = get_env_variable("POSTGRES_USER") POSTGRES_URL = get_env_variable("POSTGRES_URL") # the values of those depend on your setup Message = "Expected environment variable '' not set.".format(name) The function which is used to get the value of an environment var, and STOP EVERYTHING otherwise looks like this: def get_env_variable(name): If the environment is not configured correctly and fix it. I like to choose the crash and burn approach, as that makes it very easy to notice If not, we could rely on default values orĬomplain. In the simplest case, we want our app to check if they’re there. Here are the values those variables need to have, in case you are using a Docker-based setup as described The export means that the variable is avilable to programs being started afterwards and isn’t just available in the current bash session only. Just append lines like the following one to it: export VARIABLE_NAME=value In Ubuntu, you can set those variables using bash.įor the development environment, I usually just add them to the bin/activate of the virtualenv, which is a bash script. TheĮnvironment tells it what it needs to know. This way, your app does not really change nor care where it’s running. You just look up a value you need willīe available, and use it. Luckily, you can always access “environment variables” from within programs. You’d need to have two different versions of the code, and that’d What happens if you want to deploy the app to a production server? You’ll want to have a proper usernameĪnd a password which is an actual password. Want to develop your app locally, and use your trusty development database with user test and password test. Those can be hardcoded, which is considered to be in poor taste. Or at least you need to tell your app what database to connect to, and what If you look into the file, you’ll see that not only the package names but the precise versions are saved.Īnd not only of the packages you installed implicitly, but also dependencies. That one’s for future-you to save time and be less angry :) The currently installed packages can be written to a file without much effort: $ pip freeze -local > requirements.txt Usually, you save the dependencies of a project in a requirements.txt file, so it’s easy to get it to run Also, you will not break one project by upgrading another. Using a virtualenv is a good idea, so your development machine is not littered with all kinds of development dependencies for different projects. Once those are in place, we can install the Python modules with pip in the following way: pip install flask-sqlalchemy psycopg2 $ sudo apt-get install psycopg2 libpq-dev python-dev They are called psycopg2, libpq-dev and python-dev. If you’re on Ubuntu, you will need a few more libraries to install those with pip. We will need a few additional Python modules in our project to talk to the PostgreSQL database. Our starting point is the Flask app here. Stuff instead of just emitting “Hello World”. To the PostgreSQL database which we are able to launch in a Docker container, and start doing useful Let’s connect our Flask app from the previous article The data is saved in another service, which is made to be really good at handling it and making it accessible. Horizontal scaling, spinning up multiple instances of your app, is possible without breaking everything. They don’t have something which needs to be remembered - a state. Modern webapps are meant to be stateless. Using SQLAlchemy with Flask to Connect to PostgreSQL
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