1. 11 Version control (part 2)
Objektorienterade applikationer d2, förel. 11
11 Version control (part 2)
(Hodson: 2-, Chacon: 3, 4.10, 5)
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2. Main concepts to be covered
Objektorienterade applikationer d2, förel. 11
Main concepts to be covered
The git repository architecture.
Stage, commit and undo.
Branching, merging and rebasing.
Local and remote repositories.
Workflow models.
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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3. Objektorienterade applikationer d2, förel. 11
Safety warning
When You are learning GIT
always keep safety backups
of your code!
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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4. Objektorienterade applikationer d2, förel. 11
Git overview
Here you work
with your code
using your favourite tools
Stores the revision
history of your project
Repo
Working
directory
Staging Area
(index)
Stage
Commit
History
Here you prepare
your commits
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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5. The three main parts of Git
Objektorienterade applikationer d2, förel. 11
The three main parts of Git
The repository (git directory) contains metadata and object database.
The working directory is a working copy of one version of the project files.
The staging area (index) is a file describing the contents of the next commit.
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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6. File status in the working directory
Objektorienterade applikationer d2, förel. 11
File status in the working directory
tracked
add the file
modified
edit the file
unmodified/
committed
untracked
stage the file
commit
remove the file
staged
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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7. Objektorienterade applikationer d2, förel. 11
Git snapshots
Committed snapshot
Files in the
snapshot
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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8. Objektorienterade applikationer d2, förel. 11
Staging files
Collect related changes in the working directory and prepare them for commit
> git add <file>
Working
directory
Staged Snapshot
Stage
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9. Objektorienterade applikationer d2, förel. 11
Committing a snapshot
A commit is a saved version of the project.
> git commit
A commit is identified by a unique checksum of its contents.
Repo
Staged Snapshot
Commit
History
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10. Objektorienterade applikationer d2, förel. 11
Commit contents
A commit contains
A snapshot of the project
A checksum of the contents
User information
The date
A short description provided by the user
Commit c8e7c491af652b9c73d Author: lisa Date: Thu Feb 12 15:31:
<commit message>
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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11. Branches, master and HEAD
Objektorienterade applikationer d2, förel. 11
Branches, master and HEAD
A branch is a pointer to a commit.
The default branch is called master.
The pointer moves forward with each commit.
master
Commit
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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12. Branches, master and HEAD
Objektorienterade applikationer d2, förel. 11
Branches, master and HEAD
A new branch is created by
> git branch <name>
Ex: > git branch my-branch
head
head keeps track
of the current branch
master
my-branch
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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13. Objektorienterade applikationer d2, förel. 11
Checking out a branch
Switch to a branch with checkout:
> git checkout <name>
Ex: > git checkout my-branch
master
my-branch
This is now
the current branch
head
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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14. Objektorienterade applikationer d2, förel. 11
Splitting the history
Commit to the new branch
> git commit
master
my-branch
head
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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15. Objektorienterade applikationer d2, förel. 11
Splitting the history
Do some work on the master branch
> git checkout master > git commit
head
head
master
master
Commit
my-branch
my-branch
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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16. Undoing in working directory
Objektorienterade applikationer d2, förel. 11
Undoing in working directory
Restore the working directory and stage to match the most recent commit (HEAD):
> git reset –-hard HEAD
> git clean -f
Undo changes in tracked files
Remove untracked files
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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17. Undoing in the staging area
Objektorienterade applikationer d2, förel. 11
Undoing in the staging area
Restore a file in the stage to match the most recent commit (HEAD):
> git reset HEAD <file>
This does not affect the file in the working directory.
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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18. Objektorienterade applikationer d2, förel. 11
Undoing commits
Reset moves HEAD backwards in history:
> git reset HEAD~1
One step before HEAD
Forget last commit
Only use reset on local repositories
- never on public ones!
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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19. Objektorienterade applikationer d2, förel. 11
Undoing commits
Revert adds a new commit that “neutralizes” the changes in the specified commit:
> git revert <commit-id> + -
Neutralizing commit
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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20. Objektorienterade applikationer d2, förel. 11
Undoing commits
Amend replaces the most recent commit:
> git commit --amend
Ooops!
Forgot a file in the last commit  
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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21. Master and topic branches
Objektorienterade applikationer d2, förel. 11
Master and topic branches
Use the master branch for stable code.
Develop new features in topic branches.
Only commit to topic branches, not to the master branch.
Integrate successful topic branches into master.
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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22. Objektorienterade applikationer d2, förel. 11
Fast-forward merge
master
master
some-feature
some-feature
Topic branch
> git checkout master
> git merge some-feature
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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23. Objektorienterade applikationer d2, förel. 11
3-way merge
master
master
some-feature
some-feature
> git checkout master
> git merge some-feature
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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24. Rebasing makes history linear
Objektorienterade applikationer d2, förel. 11
Rebasing makes history linear
Old base
Old base
master
master 1
some-feature 2
some-feature
master
> git rebase master some-feature (1)
> git checkout master (2)
> git merge some-feature #ff (2)
> git branch –d some-feature (3)
some-feature
(3)
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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25. Objektorienterade applikationer d2, förel. 11
Remote repositories
A remote branch is a copy of a branch in some developer’s repository.
Local branch
master
Remote repo
Remote branch
> git fetch <remote> <branch>
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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26. Objektorienterade applikationer d2, förel. 11
Remote repositories
Cloning a remote repository creates a local copy into the current directory. > git clone <path-to-repo>
Ex. > git clone
A remote is an alias for a remote repository
> git remote add <name> <path-to-repo>
Ex.
> git remote add other
# other can now be used as a ”bookmark” to friend’s repo.
# (btw, this is a git comment!)
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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27. What does “origin” mean?
Objektorienterade applikationer d2, förel. 11
What does “origin” mean?
When a remote repository is cloned, origin is by convention the local default alias for the remote repository.
origin/master is a local copy of the master branch at the remote repository.
The command git push origin master updates the remote master branch with the local master branch. (for example at GitHub).
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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28. Objektorienterade applikationer d2, förel. 11
origin
Remote repo
master
master
Current state of remote master branch
clone
origin
Old state of remote master branch
Local repo
origin/master
Current state of local master branch
master
Local copy
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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29. Merging a remote branch
Objektorienterade applikationer d2, förel. 11
Merging a remote branch
To use a remote branch it has to be integrated in your own repository by merge or rebase.
> git checkout master
> git fetch origin
> git merge origin/master
origin/master
origin/master
origin/master
Merge commit
merge
Remote branch
Local branch
master
master
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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30. Rebasing onto a remote branch
Objektorienterade applikationer d2, förel. 11
Rebasing onto a remote branch
Integrating a remote branch with rebasing:
> git checkout master
> git fetch origin
> git rebase origin/master
origin/master
origin/master
master
master
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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31. Objektorienterade applikationer d2, förel. 11
Push
push exports a branch to a remote repository.
> git push <remote> <branch>
origin/master
origin/master
Use push to upload
changes to your own
public repository.
Allways fetch the remote branch and merge or rebase with your local branch before pushing!
master
master
Ex.
> git checkout master
> git fetch origin
> git merge origin/master
> git push origin master
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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32. Objektorienterade applikationer d2, förel. 11
Pull
A pull is a combined fetch of the remote master branch followed by a merge with the current branch:
> git pull
Pull can be used with the --rebase option to perform a rebase instead of a merge.
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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33. Distributed workflows
Objektorienterade applikationer d2, förel. 11
Distributed workflows
Centralized workflow
Integration-manager workflow
Exercise (last page)
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34. Distributed workflows
Objektorienterade applikationer d2, förel. 11
Distributed workflows
Develop some new feature.
Rebase it onto your local master branch.
Push master to your public repository.
Never rebase onto public branches!
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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35. Objektorienterade applikationer d2, förel. 11
Centralized Workflow
Public version
Public repo
clone/pull
push
Developer
Developer
Local repo
Developer
Local repo
Local repo
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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36. Integrator-Manager Workflow
Objektorienterade applikationer d2, förel. 11
Integrator-Manager Workflow
Master repo
Public repo 1
Public repo 2
Public repo 3
2. clone
3. push
1. push
5. push
4. pull in
contributions
Main
Developer 2: Main
Local repo 2 B
Developer 3: Feature B
Local repo 3
Integration manager
Local repo 1 A
Developer 1: Feature A
Local repo
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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37. Exercise (see separate PM)
Objektorienterade applikationer d2, förel. 11
Exercise (see separate PM)
local repo 1
remote repo 1
remote repo 2
local repo 2
clone
push
(edit;
add;
commit)*
fetch
merge or
rebase *
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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38. Exploring version differences
Objektorienterade applikationer d2, förel. 11
Exploring version differences
public class PrimeGenerator implements Generator<Integer> {
private int currentPrime = 1;
public Integer next() {
return currentPrime; }
private boolean isPrime(int n) {
for ( int f = 2; f < (int)Math.sqrt(n); f++)
if ( n % f == 0 )
return false;
return true;
private boolean isPrime(int n) {
int factor = 2;
while ( factor <= (int)Math.sqrt(n) ) {
if ( n % factor == 0 )
return false;
factor++; }
return true;
Suppose isPrime
above is changed
to this version
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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39. Exploring version differences
Objektorienterade applikationer d2, förel. 11
Exploring version differences
Lines 18-19
are replaced by
old line 20
is now 21
Some new
lines added
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3. (c)2017 Uno Holmer, DIT, Chalmers
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40. Difference visualization in the SmartGit tool
Objektorienterade applikationer d2, förel. 11
Difference visualization in the SmartGit tool
Lines 18-19
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41. Difference visualization in the SmartGit tool
Objektorienterade applikationer d2, förel. 11
Difference visualization in the SmartGit tool
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42. Difference visualization in the SmartGit tool
Objektorienterade applikationer d2, förel. 11
Difference visualization in the SmartGit tool
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43. Objektorienterade applikationer d2, förel. 11
A branching model
An advanced, but realistic, branching model is described in:
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