Using Git Source Control

This Site is still a Work in Progress!!

Git is a popular source control system for saving and sharing one's code with other developers working on the project (i.e. have access to the shared remote repository).

Git can be run from the command line or from inside Eclipse, IntelliJ, Visual Studio and other integtrated development environments (IDE's).

GitHub is a popular cloud-based Git repository service that can be used as the remote Git repository for projects. Bitbucket is another popular cloud-based, remote Git repository service.

IMPORTANT Git ARCHITECTURE INFORMATION

The Git architecture uses TWO repositories!

1. Local repository -- Holds repository information on your computer's disk.
   • Any data in this local repository WILL be LOST if your computer disk fails!!
   • A simple "commit" will ONLY save your code to the local repository!
   • The local repository is NOT shared amongst multiple developers on a project. Commits to the local repository are not accessible by other developers!
2. Remote repository -- Holds repository information on a remote (e.g. cloud) system.
   • Any data in this remote repository will be SAVED if your computer disk fails!!
   • You must "PUSH" your code to save it to the remote repository!
   • Only the remote repository is shared amongst multiple developers on a project. Code that is pushed to the remote repository is accessible by all developers on the project.

ALWAYS PUSH TO THE REMOTE REPOSITORY!!

If an Internet connection is not available, commit to the local repository but be sure to push to the remote repository as soon as Internet connectivity is re-established! This will at least enable you to recover from editing mistakes in the interim.

 

ALWAYS

• Push to the remote repository -- don't just commit to the local repository as this risks data lost in the event of a computer failure.
• Push the ENTIRE project, not just specific files
  • Information needed by the project is often held in metadata files at the root of the project and may not be included if only specific files are selected to be pushed.

Git Terminology

• Push:
  • Save the code to BOTH the local and remote repositories.
  • The RECOMMENDED operation for saving code!!
• Commit:
  • Save the code ONLY to the LOCAL repository.
  • NOT RECOMMENDED!!!
• Pull:
  • Download objects, e.g. code files, from a remote repository AND merge them with the currently checked out items.
  • The typical operation when updating one's code with changes from another developer.
• Fetch:
  • Download objects, e.g. code files, from a remote repository.
  • Does NOT merge the downloaded items with the currently checked out items!
    • Any changes relative to the checked out code can be viewed and applied manually after the fetch completes.
• Origin:
  • An alias used by Git to represent the name of the remote repository linked to the local repository.
• Pull Request:
  • A request to other developers to pull the latest changes from the remote repository and review those changes.
• Clone:
  • Copies a remote repository to the local system, creating a local repository linked to the remote repository.
• Submodules:
  • Secondary repositories that are included in a project that enable code from multiple sources to be combined in a project.
  • Submodules are used to enable multiple projects to use shared library code
  • It is common for developers NOT to have write permissions to submodule repositiories so the code in those libraries should not generally be edited.
  • Updating the code in submodules is a separate process from updating the code from the main repository.

Tips and Traps

Other developers can't see the changes in the committed code

Make sure that the changes have been pushed all the way to the remote repository.

 

"'submodule_folder' already exists in the index" error message

This error message can occur after removing a submodule and then trying to re-add a submodule iat the same location in the project folder hierarchy, i.e. the location indicated by 'submodule_folder'. This error can occur even after removing all references to the removed submodule from the .gitmodules and .git/config files.

The problem is that Git views the removal of the submodule folder as a "staged" change and is still keeping references to it in its index. To get rid of the error and enable proceeding to add the new submodule at the same location, the folder location must be "unstaged":

1. Open a terminal window at the root of the desired project.
   • Eclipse: Open a "Terminal+" view (NOT the regular "Terminal" view) because this terminal view is configured to run Git.
2. To "unstage" the folder, run the following command, where the full pathname of the problematic folder relative to the project root is substituted for "submodule_folder" (i.e. the folder name as displayed in the error message):
   git rm -r submodule_folder

Refs:

• git - Add a submodule which can't be removed from the index - Stack Overflow

 

 

 

 

Using submodules

svn:externals equivalent by having submodules track latest version: SVN:externals equivalent in Git? - Stack Overflow

Git Submodules vs Git Subtrees | Martin Owen (martowen.com)

The Rebase controversy -- spawn of the devil?

Using Git

• Eclipse
• IntelliJ
• Command line
• Others
  • Git GUI clients are available for most desktop operating systems plus iOS and Android. Most apps are free.

References

• Git
  • About Git -- Information about the Git source control system, independent of GitHub.
  • Sub-topics:
    • Submodules
• GitHub
  • GitHub Docs Home -- Includes:
    • Reference Manual
    • "Pro Git" book
    • Tutorial Videos
    • Links to 3rd party materials
  • GitHub "Cheat Sheet"
    • "Visual" Cheat Sheet -- interactive, graphical display of commands and the directions in which they move data in the system. Click on one of the colored columns to start.

© 2021 by Stephen Wong