Setting Up the Environment
The process of building a web application can be a daunting task, and setting up a database can make the process even more challenging. In this article, we will discuss how to set up a Postgres database with SQLAlchemy and Alembic for database migrations.
We will also cover how to define data models and perform local migrations using Flask-Migrate and manage.py. By the end of this article, you will have gained a deeper understanding of how to set up and manage a Postgres database within a Flask web application.
To begin setting up the environment, we need to install all the required dependencies. The primary requirements to install are Postgres, SQLAlchemy, and Alembic.
These tools will help us to perform different database-related tasks.
Updating Configuration
After installing the required dependencies, we need to set up the configuration. This configuration can be done using environment variables.
We will set the SQLALCHEMY_DATABASE_URI variable, which will help our application to create a connection to the Postgres database. It is important to configure the database in the correct environment, such as development, production, or testing.
Once the configuration is done, we can move onto defining the data models and performing the local migration.
Data Model and Local Migration
Data Model
The first step in setting up the data model is to define the complete database schema. We create a single object-relational mapping class that will represent the database table and columns.
We then define the columns in the table, including their data type, length, and other constraints. Along with normal columns, we can also create JSON columns, which can store JSON data in the column.
This can be useful when storing non-tabular data, like settings, preferences, or user-defined metadata.
Local Migration
One of the most important parts of the database setup is to migrate database schema changes from the development environment to the production environment. To do this, we use Alembic, which is a database migration tool that provides a simple way to define database schema changes.
Alembic creates different versions of the database schema, and we can apply these changes to the different environments using Flask-Migrate and manage.py. Flask-Migrate is an extension that simplifies handling the Alembic migrations for Flask applications.
Manage.py is a command-line utility that allows us to perform common tasks in Flask applications.
Conclusion
Setting up a database can be a tedious task, especially when it comes to migrating the database schema changes from one environment to another. However, by following the steps outlined in this article, you can simplify the process of setting up a Postgres database, defining data models, and performing local migrations.
With this knowledge, you can build web applications more efficiently with a well-structured database that will scale well as your application grows. In the previous sections, we have discussed how to set up and perform local migrations on a Postgres database.
However, when an application is deployed, it is usually run on remote servers. In this section, we will discuss how to perform remote migrations on a Heroku staging app and production app.
Remote Migration
Heroku is a cloud platform that allows you to deploy applications easily. Heroku provides addon services, one of which is the PostgreSQL addon service.
This service provides a managed Postgres database service that can be easily integrated with your Heroku application. Heroku also provides an easy way to perform remote migrations using the Heroku CLI.
Before we perform a remote migration, we need to make sure that our Heroku applications are set up correctly. We have two types of applications in Heroku, namely the staging app and production app.
The staging app is where we deploy our pre-production code, and the production app is where we deploy our final product.
Once the Heroku applications are set up, we need to provision the Postgres addon service to both the staging and production apps.
This can be done by running the following Heroku CLI command:
heroku addons:create heroku-postgresql:hobby-dev --app After provisioning the Postgres addon service, Heroku will create an instance of the database service and will set the DATABASE_URL environment variable in the app environment. This DATABASE_URL will point to our Postgres database instance.
To begin a remote migration, we first need to create a migration script on the local development machine. This can be done using Alembic, just like we did for local migrations.
After creating the migration script, we need to apply it to the staging app. To do this, we need to push the changes to the Git remote repository and then execute the following command:
heroku run python manage.py db upgrade --app This will apply the migration script to the staging app.
After applying the migration script, we should test the changes on the staging app before deploying them to the production app. To perform production migrations, we follow a similar process to the staging migrations.
We first need to add the migration script locally, commit it, and push it to the Git remote repository. We then execute the following command:
heroku run python manage.py db upgrade --app This will apply the migration script to the production app.
We should always be careful while performing production migrations since any error during this phase can cause data loss or corruption. It is important to note that we should always have a backup of our database before performing any migration on a production app.
This will provide us with a safety net that we can rely on if anything goes wrong. We can perform a backup of our database using the following Heroku command:
heroku pg:backups capture --app This will capture a backup of our production database, and we can later restore it if needed.
Conclusion
Performing remote migrations on a Heroku app is an essential part of the deployment process. We need to make sure that we set up our staging and production apps correctly and provision the Postgres addon service to both of them.
We can apply migrations to both staging and production apps using the Heroku CLI. We should always be careful while performing production migrations and have a backup of our database to fall back on if anything goes wrong.
By following these steps, we can ensure that our database schema changes are propagated correctly in both the development and production environments. In this article, we have discussed how to set up and manage a Postgres database within a Flask web application.
We have covered how to install the required dependencies, update the configuration, define data models, and perform local and remote migrations. Local migrations use Alembic, Flask-Migrate, and manage.py to propagate schema changes in the development environment.
Remote migrations use Heroku, which is a cloud platform that allows for easy deployment and remote migrations. By following the steps outlined in this article, developers can effectively set up and manage their Postgres databases in both local and remote environments, with changes safely propagated across them.