Exercise - Modularization with Subtrees
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 is git subtree. We will try both here for the following use cases:
- Integrating modules as subtrees
- Adopting changes from a module
- Transferring changes to a module
- Cloning the parent repo
Subtrees
In this approach, commits from the subordinate repository are transferred and integrated via merge, very similar to a normal pull. The special feature is that for integration, a so-called subtree merge takes place, in which the files are moved to a specified target directory (prefix).
subtree add --prefix=<target-directory> <source-repository>: Initial embedding.subtree pull --prefix=<target-directory> <source-repository>: Update from the source repository.subtree push--prefix=<target-directory> <source-repository>: Transfer to the source repository.
Tip: If you don’t like that subtree fetches all commits from the source repository, you can use the --squash option.
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 subtrees
Start in directory git-uebungen/aufgaben/<unknown>.
Integrate the modules frontend.git and backend.git using subtree 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 repo and fetch the changes using subtree pull. Look at the transferred commit.
Step 3 - Transferring changes to a module
Start in directory git-uebungen/aufgaben/<unknown>.
Go to application, change frontend/main.ts and commit. Transfer the change to frontend.git using subtree 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 HEAD directory structure, and the commit graph.