1. CS5220 Advanced Topics in Web Programming Version Control with Git
Chengyu Sun
California State University, Los Angeles

2. Roadmap Basic version control concepts and operations
Tag, branch, merge, and rebase
Remote repositories and collaboration

3. The Process of Application Development
Initial coding
Prototype
Add more
features
Release
Version 1.0
New feature
development
and bug fixes
Release
Version 2.0 …

4. Problems During Development
Initial coding
Prototype
Add more
features
New feature has broken existing code.
Release
Version 1.0
How do we find out which part of the code has been changed?
How do we revert back to the previous version?
New feature
development
and bug fixes
Release
Version 2.0 …

5. Problems During Development
Initial coding
Prototype
Add more
features
Can we give the customer the development version with the bug fix?
Do we still have the Version 1.0 code?
Release
Version 1.0
New feature
development
and bug fixes
Customer 1 requests a feature or
bug fix.
Release
Version 2.0 …

6. Problems During Development
Initial coding
Prototype
Where do we put in the bug fix?
Version 1.0
Version customer 1’s feature / bug fix
Development version
Add more
features
Release
Version 1.0
New feature
development
and bug fixes
Customer 2 requests a feature or
bug fix.
Release
Version 2.0 …

7. Problems During Development
Initial coding
Prototype
Add more
features
Release
Version 1.0
How many different versions do we need to maintain?
New feature
development
and bug fixes
Customer n requests a feature or
bug fix.
Release
Version 2.0 …

8. Problems During Development
Initial coding
Prototype
Add more
features
How do we collect all the bug fixes into one release?
Release
Version 1.0
Put all changes into an
intermediate release.
New feature
development
and bug fixes
Release
Version 2.0
Release
Version 1.1 …

9. Version Control Systems
CVS
Used to be the most popular / well known / widely used open source version control system
Obsolete due to some inherent system limitations
Open Source
Git, Subversion, …
Commercial
Team Foundation Server, ClearCase, …

10. Why Git?
Popularity
GitHub

11. A Little History …
1991 – Linus Torvalds started the development of Linux
2001 – Linux Kernel 2.5 Release
More than 3 million lines of code
Hundreds of developers from all over the world
Individual use of version control (mostly CVS)

12. … A Little History
2002 – BitKeeper adopted as the version control system for Linux kernel
Good system for large, distributed software development
Proprietary software and restrictive license terms
2005
End of the use of BitKeeper for Linux kernel development
Linus Torvalds created Git (there is no going back to CVS!)

13. Using Git Command line: git
GUI: IDE integration in Eclipse, IntelliJ IDEA, Android Studio, Visual Studio …

14. Version Control A Project
Unmanaged Copy
Repository
/project
file1
file2 …
/project
file1
file2 …
/project
file1
file2 …
/project
file1
file2 …
Working Copy
/project
/special folder used by VCS
file1
file2 …
Versions
(Revisions)

15. Git Init Run git init in the project folder
Creates a repository for the project (under /.git)
Makes the current project folder a working copy (also using /.git)
No files are under version control yet

16. Share Project in Eclipse
Right click on the project and select Team  Share Project …
Performs git init for an unmanaged project, or
Makes Eclipse aware of the repository for a project that’s already under version control

17. What Files Should Be Under Version Control?
The minimal set of files that needed to build the project
Examples
Build file, e.g. pom.xml??
Source code, e.g. java files??
Generated files, e.g. class files??
Graphic assets, e.g. images and icons??
Libraries, e.g. jar files??
Eclipse project files: .project, .classpath, .settings

18. The Files That Should Not Be Under Version Control
.gitignore
/target/
/test-output/
/.project
/.classpath
/.settings/
See for more gitignore patterns.

19. Commit – Save Changes to Repository
/project
file1
file2 …
Working Copy
/project
file1
file2 …
/project
file1
file2 …
/project
file1
file2 [Modified]
file3 [Added] ….
commit
Versions
(Revisions)

20. The Git Index A.K.A. The staging area or cache
Technically Git only commits files added to the index (i.e. staged)
Command line option and GUI can simplified this intermediate step
Working Copy
Index
Repository
/project
file1
file2 [Modified]
file3 [Added] ….
file2 [Modified]
file3 [Added]
add
commit

21. A Few Common Version Control Operations
status: check which files are added/modified
diff: see the changes
revert: undo the changes
log: see the commit

22. Roadmap Basic version control concepts and operations
Tag, branch, merge, and rebase
Remote repositories and collaboration

23. Recall an Earlier Version of a Project
Repository
In any VCS, it’s always possible to recall an earlier version of a project
In Git, each commit has an unique ID, which is the SHA-1 hash of the repository after the commit
1c96400
6da4b3a
The version after commit

24. Tag – Give Some Versions More Memorable Names
Repository
1c96400
Tag
“version-1.0”
git tag –a version-1.0 –m “Tag version 1.0”
Annotated tags for very important versions, e.g. releases
Lightweight tags for somewhat important versions, e.g. used as reminders for yourself

25. Branch – Work in Parallel
version-1.0 c1 c2 c3 c4
master c5 c6
v1-c1-branch
Create a branch based on version 1.0 to added the feature requested by Customer #1

26. Merge – Copy Changes Between Branches
git merge <branch>
Copy the changes from <branch> to the current branch

27. Fast-Forward Merge …
master c1 c2 c3
Created
branchA c4 c5
branchA

28. … Fast-Forward Merge
git merge branchA c1 c2 c3
master c4 c5
branchA

29. Three-Way Merge … master c5 c1 c2 c3 c4 git merge branchA branchA
“Hello World” c1 c2 c3 c4
“Hello CS5220”
git merge branchA
Should we keep “Hello
World” or “Hello CS5220”
after the merge??
branchA

30. … Three-Way Merge master c5 c1 c2 c3 c4 git merge branchA branchA
“Hello CS5220” c5
“Hello World” c1 c2 c3 c4
“Hello CS5220”
git merge branchA
Should we keep “Hello
World” or “Hello CS5220”
after the merge??
branchA

31. Merge Conflict master c5 c1 c2 c3 c4 branchA “Goodbye” “Hello World”
“Hello CS5220”
branchA

32. Manually Resolve Merge Conflict
Manually edit the file
Add the edited file to Git index to indicate the conflict is resolved

33. After Merge master c5 c6 c1 c2 c3 c4 branchA c6 is called a
“merge commit’ c4
branchA

34. Rebase …
master c5 c6 c1 c2 c3
branchA c4

35. … Rebase
Takes the changes made in c4 and apply them to c5 to create c6
Rewrite history to make it looks like branchA started from c5 instead of c3

36. About Rebase
c6 has the same content whether it’s from a merge or a rebase
Rebase makes for a cleaner history
Think of rebase as a merged performed by the person in charge of branchA instead of the person in charge of master
There are some other trickier usage of rebase because of its ability to rewrite history

37. Roadmap Basic version control concepts and operations
Tag, branch, merge, and rebase
Remote repositories and collaboration

38. Centralized VCS vs. Git Centralized VCS Git ?? Repository Repository
Working Copy
Working Copy
Repository ??
Working Copy
Working Copy
Working Copy

39. Git Remote Setup (I) Remote Repository
Local Repository
Local Repository
Local Repository
Working Copy
Working Copy
Working Copy
Working copy does not interact with remote repository directly.

40. Git Remote Setup (II) Remote Repository Remote Repository Remote
Local Repository
Local Repository
Local Repository
Working Copy
Working Copy
Working Copy
A local repository can interact with many remote repositories.

41. Create A Remote Repository
Create a remote repository on GitHub
Push the local repository to GitHub
git remote add origin <url>
Add a remote repository called “origin” at the <url>
git push -u origin master
Push the local master branch to the master branch in the
remote repository called origin
Set up the local master branch as a tracking branch of the
remote branch origin/master

42. Understand Push – In The Beginning
Local Repository
Remote Repository c1 c1 c2 c2
master
origin/master
master

43. Understand Push – After A Local Commit
Local Repository
Remote Repository c1 c1 c2 c2
origin/master
master c3
master

44. Understand Push – After Push
Local Repository
Remote Repository c1 c1 c2 c2 c3 c3
master
origin/master
master
A “tracking branch” simply tells Git which branch the changes
should be pushed to (or fetch/pull from).

45. Fetch – Somebody Else Pushed A Commit to Remote
Local Repository
Remote Repository c1 c1 c2 c2 c3 c3
master
origin/master c4
master

46. Fetch – After Fetch Local Repository Remote Repository c1 c1 c2 c2 c3
master c4 c4
origin/master
master

47. Pull = Fetch + Merge Local Repository Remote Repository c1 c1 c2 c2 c3
master
origin/master
master

48. Git Clone Create a local repository from a remote repository
Git Clone in Eclipse
Use Git Perspective
The default repository location is under $USER/git (i.e. outside Eclipse workspace)
Need to perform a project import after the repository is created

49. GitHub Fork Somebody else’s Account Your Account Fork GitHub
Repository
Repository
Clone
Local
Repository

50. Collaboration Models
Different ways a team of developers collaborate on a project
Centralized
De-centralized

51. Developer (Team Leader)
Centralized Model
Remote
Repository
Local Repository
Local Repository
Local Repository
Working Copy
Working Copy
Working Copy
Developer
Developer (Team Leader)
Developer

52. About Centralized Model …
Each developer work on their own branches
A team leader is in charge of the important branches (e.g. master)
Changes can be copied between branches using merge/rebase
Similar to using a centralized VCS

53. … About Centralized Model
All developers need write access to the same repository
Repository “collaborators” on GitHub

54. Developer (Team Leader)
De-Centralized Model
GitHub Pull Requests
Official
Repository
Remote
Repository
Remote
Repository
Local Repository
Local Repository
Local Repository
Working Copy
Working Copy
Working Copy
Developer (Team Leader)
Developer
Developer

55. About De-Centralized Model
Each developer work with their own remote repository
A team leader maintains the “official” project repository
Changes can be exchanged using Git remote operations or GitHub Pull Requests
The more “git way” of collaboration

56. GitHub Pull Request … A request made by developer A to developer B
Requesting some changes made by A to be merged into B’s repository
Include two branches and some description of the changes
A branch in A’s repository (where the changes are)
A branch in B’s repository (where the changes will be merged to)

57. … GitHub Pull Request GitHub support for pull requests
notifications
Detection of merge conflicts
Easy-to-use web UI for non-conflict merges
Instructions for merges with conflicts

58. Readings
Pro Git -