About 10 years ago I wrote a post PostgreSQL for the Busy MySQL Developer, as part of switching from MySQL to Postgres for my personal and professional projects, wherever I could.

Recently I had the chance to work with Python, Django, and Postgres together, as a long-time and busy Rails developer.

There were some things I thought were really nice. So am I switching?

The team I worked with was experienced with Django, so I was curious to learn from them about popular libraries, idiomatic code, and tooling.

In this post, I’ll briefly cover the database parts of Django using Postgres of course, highlight some libraries and tools, and compare things to Ruby on Rails. You’ll find a small Django repo towards the end as well.

Ruby versus Python

Ruby and Python are both general purpose programming languages. On the similarity side, they can both be used to write script style code, or organize code into classes using object oriented paradigms.

In local development, it felt like the execution of Python was perhaps faster than Ruby, however I’ve noticed that new apps are always fast to work with, given how little code is being loaded and executed.

Language runtime management

As a developer we typically need to run multiple versions of Ruby, Python, Node, and other runtimes, to support different codebases, and to avoid modifying our system installation.

In Ruby I use rbenv to manage multiple versions of Ruby, and to avoid using the version of Ruby that was installed by macOS, which is usually outdated compared with the version I want for a new app.

In Python, I used pyenv to accomplish the same thing, which seemed quite similar in use.

Both have concepts of a local and global version, and roughly similar commands to install and change versions.

Library management

In Ruby on Rails, Bundler has been the de facto standard forever, as a way to pull in Ruby library code and make sure it’s loaded and accessible in the Rails application.

In Python, the team selected the poetry dependency management tool.

Commands are similar to Bundler commands, for example poetry install is about the same as bundle install.

Dependencies can be expressed in a pyproject.toml file and poetry creates a lock file with specific library versions. TOML and YAML are similar.

Linting and formatting

In Ruby on Rails, although I personally resisted rule detection etc. for years, Rubocop has become the standard, even being built in to the most recent Rails version 8.

Rubocop has configurable rules that can automatically reformat code or lint code for issues.

Formatters like standardrb are commonly used as well.

For the Django app, the team selected ruff, which performed formatting of code and also linted for issues like missing imports.

I found ruff fast and easy to use and genuinely helpful.

For example, sometimes I’d fire up a Django shell, skipping ruff, only to realize there are issues it would have caught.

On this small codebase, ruff ran instantly, so it was a no-brainer to run regularly, or even include in my code editor.

Postgres adapter

In Rails and Django, SQLite is the default database, however I wanted to use Postgres.

In Ruby, we have the pg gem which connects the application to Postgres as a driver. This does work at a lower level than the application like sending TCP requests, mapping Postgres query result responses into Ruby data types, and much more.

In Python, we used the psycopg2 library and I found it pretty easy to use.

Besides being used by the framework ORM, I created a wrapper class using psycopg2 to use for sending SQL queries outside of models.

For example, we inspected Postgres system catalog views to capture certain data as part of the product features.

Migrations in Rails

Both Ruby on Rails and Django have the concept of Migrations, which are Ruby or Python code files that describe a database structure change, and have a version.

From the Ruby or Python code files, SQL DDL (or DML) statements are generated which are run against the configured database.

For example, to add a table in Rails typically a developer uses the create_table Ruby helper as opposed to writing a CREATE TABLE SQL statement.

Adding or dropping an index or modifying a column type are other types of DDL statements that typically are performed via migrations.

Migrations in Django

The Django approach has noteworthy differences and a slightly different workflow that I enjoyed more in some ways.

For example, changes are started in a models.py file, which contains all the application models (multiple models in a single file), and the database layer details about each model attribute.

This means that we specify database data types for columns, whether fields are unique, indexed, and more in the models file.

The interesting difference compared with Rails is that the next step in Django is to run makemigrations, which generates Python migration files.

This is different from Rails, where Rails developers would first generate a migration file to place changes into.

In Django, the generated migration file can be inspected or simply applied using the migrate command. This command is nearly identical to the Rails equivalent command db:migrate.

For a new project where we were rapidly iterating on the models and their attributes, I preferred the way Django works here to how Rails works.

Command line vibes

Here are some commands like running poetry install, or running manage.py commands like shell or makemigrations, to give you a flavor.

poetry install
poetry run python manage.py dbshell   # psql in postgres
poetry run python manage.py shell # Django shell
Poetry run python manage.py makemigrations   # Generates Python migration files, can be customized
Poetry run python manage.py migrate # runs them. Doesn’t show SQL by default.

Interactive console (REPL)

Both Django and Rails use interpreted languages, Python and Ruby respectively, that each support an interactive execution environment.

This environment is called a read, eval, print loop or REPL for short.

In Rails, the Ruby REPL “irb” is launched and Rails application code is loaded automatically when running the rails console command.

In Django, the equivalent command is running shell, however application code needs to be imported before it can be used, using import statements.

Both frameworks also support opening a database client, by running dbconsole in Rails or dbshell in Django.

When Postgres is configured, these both open a psql session.

Projects and Apps

In Django, projects and applications are separate concepts.

In my experimental project, I made a “booksproject” project and a “books” app.

Check out the booksproject repo.

Postgres details

The books app models are Author, Publisher, and Books.

The tables for those models are contained in a custom schema booksapp, and Django is configured to access it.

The application connects to Postgres as the booksapp user and the dev database is called books_dev.

No migration safety concept

No concept of safety, adding indexes (blocking writes) doesn’t use concurrently by default.

Adding a constraint

In models, add unique=True to a field definition. After running makemigrations a migration for a unique index will be created.

In Active Record we might generate the migration file first, then fill in the create statement for a unique index.

Django models

When querying a model like Book, we’d use objects, which returns a QuerySet object with one or more books.

The filter() method will generate a SQL query with a WHERE clause to filter down the rows, or all rows can be accessed using all().

For example:

Model.objects.filter()
Model.objects.first()
Model.objects.all()

Since Python is a whitespace and indentation sensitive language, we’d indent the attributes within create() by 4 spaces, as shown below:

Thing.models.create(
    attr1=val,
    attr2=val
)

Previewing DDL

The generated SQL DDL isn’t displayed when running migrate by default.

However, unlike Rails, Django provides a mechanism to preview it.

To do that, run the sqlmigrate command instead of migrate.

For example, to print the 0001 migration DDL:

python manage.py sqlmigrate books 0001

BEGIN;
--
-- Create model Author
--
CREATE TABLE "books_author" ("id" bigint NOT NULL PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY, "first_name" varchar(200) NOT NULL, "last_name" varchar(200) NOT NULL);
COMMIT;

Resources

For the basics of an Author, Publisher, and Books models, or Postgres configuration including a custom schema and user, check out booksproject repo.

To collect random Django tips, I’ve created a django-tips page, to be used in a similar way as my rails-tips and postgresql-tips pages, mostly as a reference for myself, and possibly useful for others.

Wrap Up

Do you have any similarities and differences between Django and Rails to share? I’d love to hear from you.

😅 And no, I’m not “switching” from Rails and Ruby, but I did enjoy working with Python and Django.

Thanks for reading.