Lego bricks

In a recent post, I explained how to decompose a large codebase into Git submodules. In that occasion, I explained how we did that in the OSIS project for existing applications. This time, I’m going to explain the creation of a new submodule that isn’t a relocation of an existing application, but a brand new application for new users.

It is going to be easier this time, but it is recommended to read the previous post for more operational details. The first step is to create a new repository on GitHub for the new app. It’s better to follow the instructions there because it may change from time to time. The only suggestion I give is to follow a naming convention. In the case of OSIS, we prefix the submodules with the name of the project, followed by a dash and then the name of the app. For example:


This way, the repositories are semantically grouped:


Creating the Submodule in the Main Repository

I go to the local clone of the OSIS repository to integrate the new submodule:

$ cd ~/python/projects/osis
$ git submodule add ./mobility
$ git submodule init
$ git submodule update

Notice that I’m not allowing Git to create the directory with the default name osis-mobility. I’m passing by parameter the name I want it to be: ./mobility. I removed the prefix osis- from the name to avoid ambiguity with the main repository.

To finish, I commit the new submodule:

$ git add mobility
$ git commit -m "submodule 'mobility' added to the project."

From the Git perspective it is done. Let’s move on to Django.

The Submodule as a Django App

I’m using django-admin to generate the app in the new repository. To use it, I have to activate the project virtual environment:

$ source venv/bin/activate
$ cd mobility
$ django-admin startapp mobility .

The . after mobility is very important because it generates the files in the current directory instead of creating a new directory.

To integrate the new app, I add it to the list of INSTALLED_APPS in the file:


Then I just have to commit the new files and push the changes.

$ git add .
$ git commit -m "Initial commit"
$ git push origin master

Finally, I update the reference of the submodule to the latest commit:

$ cd ..
$ git add mobility
$ git commit -m "Updated the reference of the mobility app"

Voilà! The new app was added to the project. It’s ready to be further developed in an independent lifecycle. The previous post gives more details about what to do after that.