Exercise - Modularization with Submodules
This is about how to create a comprehensive repository in Git that embeds content from several other repositories.
Git offers two different approaches for this: One of them is git submodule. We will try both here for the following use cases:
- Integrating modules as submodules
- Adopting changes from a module
- Transferring changes to a module
- Cloning the parent repo
Submodules
With a submodule, Git repositories are nested within each other. The parent repo then remembers for each child repo (submodule)
- where to clone from (URL) and
- which revision is needed.
Since the submodules are independent Git repositories in their directories, you can work there with the usual commands like switch, pull or commit. If you want to apply the changes in the parent repo, you do this with a top-level commit.
git submodule add <source-repository> <target-directory>:> Initial embedding. Afterwards a commit is required.git submodule update --init:> Fetches or updates. Required after cloning.
Setup
Two separate repositories frontend and backend are available. These are to be embedded in a parent repo application.
application/
|- frontend/
|- backend/
Step 0 - START
$ cd application
Step 1 - Integrating modules as submodules
Start in directory git-uebungen/aufgaben/<unknown>.
Integrate the modules frontend.git and backend.git using submodule add. Then examine the resulting directory structure.
application $ cd ..
Step 2 - Adopting changes from a module
Start in directory git-uebungen/aufgaben/<unknown>.
Go to the backend repo, change the service.java file, commit and push. Look at the resulting commit (show --stat) Go to the application/backend repo and fetch the changes using pull. Look at the transferred commit.
Step 3 - Transferring changes to a module
Start in directory git-uebungen/aufgaben/<unknown>.
Go to subtrees/frontend, change main.ts and commit. Transfer the change to frontend.git using push. Look at the transferred commit in frontend.git.
Step 4 - Cloning the parent repo
Start in directory git-uebungen/aufgaben/<unknown>.
Clone application to myapplication. Examine the directory structure. Don’t forget to run submodule update.