Advanced Git(Hub)

In this lesson we'll cover branching, merging, and working with teams

Lesson Objectives

Review the basic commands for Git
Explain what a branch is and why we would use one
Create and switch between branches
Destroy a branch
Explain what a merge is and why we need them
Describe what a merge conflict is and how to resolve one
Explain the difference b/w cloning and forking a repo
Submit a pull request on GitHub for a branch
Explain the workflow for developing a project with other developers

Review

What does it mean when we say Git is a distributed version control system vs centralized?
Why do we need Git?
Revert files back to a previous state
Revert the entire project back to a previous state
See who introduced an issue and when
Automation, deployment
Benefits of working locally
Speed
Don't need to be connected to the internet to save progress
Free to experiment without impacting others
Working with Git
Working directory
Staging area
.git repository
States
Untracked
Unmodified
Modified
Staged
Commands
git init
git add
git status
git commit
git log
git branch
git checkout
git merge

Why do we need a centralized repository? (GitHub)

work in teams
backup our data in case our machine crashes
resume
social

Cloning vs Forking a repository

A clone is a copy of an existing repository. We can create as many clones as we want, wherever we want.

Forking creates a copy of someone else's GitHub repo to your GitHub account. The forked repo is not perfectly identical - but it includes all the same source files, issues, and commit history.

Used for open source contributions so that not everyone has to have write access to the code in order to contribute
Propose bug fixes

Cloning an existing GitHub repository

We Do

git clone git@github.com:ga-students/wdi-atx-7-class.git

Forking an open source project

Search for any popular repository and show how easy it is to fork into our own repository

NOTE: Students will be using a variation of the following link to submit homework:

https://www.atlassian.com/git/tutorials/comparing-workflows/forking-workflow

Fork the homework repo
Clone your version of the repo
Add a remote upstream
To get the latest updates, they will run git pull upstream master
They will then submit a pull request

Create your own GitHub repository

https://github.com/new

Initialize the repo with a README or there won't be a master branch

You Do

Clone the repository you just created on GitHub

Pushing changes back to your remote repository

git push / git push origin master

Pulling down the latest updates

git fetch - Obtains the latest updates from the remote repository
git merge - Merges the new updates with your existing working copy
git pull - A combination of both fetch and merge

We Do

Update the class repo with the Git Haiku class exercise. Have the students do a git pull to get the updates

Class Exercise - Git Haiku

20 min

https://gist.github.com/mdang/e6b45f9554a64c8d44fd

Pull Requests

Why create pull requests? What are they used for?

Branches

Branching allows you to diverge from the main line of development and continue to do work and experiment without messing up the main line.

Git stores data as a series of snapshots, with pointers to versions of files. A branch is a lightweight pointer that refers to a particular commit.

Whiteboard the main "branch", and show development branches coming out of it

The default branch name in Git is master. It's not special in any way other then it's automatically created when you use git commit. Most people don't bother to change it.

Because a branch in Git is in actuality a simple file that contains the 40 character SHA-1 checksum of the commit it points to, branches are cheap to create and destroy. Creating a new branch is as quick and simple as writing 41 bytes to a file (40 characters and a newline).

This is in sharp contrast to the way most older VCS tools branch, which involves copying all of the project’s files into a second directory. This can take several seconds or even minutes, depending on the size of the project, whereas in Git the process is always instantaneous.

Create a branch

Creating a branch creates a new pointer to the same series of commits as master

HEAD is a special pointer to the local branch that you're currently on. In this case it's still master because we haven't switched to our new branch yet.

# This creates the branch but doesn't switch to it
git branch testing

# This creates the branch and switches to it
git checkout -b testing

Switch between branches

HEAD now points to our testing branch.

Switching branches changes the files in your working directory

git checkout testing

Merge a branch

Check out the branch you wish to merge into and then run the git merge command

git checkout master
git merge testing

To update the current branch with changes from master, merge master into the branch

git checkout testing
git merge origin/master
git push origin master

Alternatively, you can rebase:

git fetch
git rebase origin/master

Destroy a branch

git branch -d testing

Merge conflicts

While running git merge, if you edited part of a file that would be further altered by the merge, you'll get a merge conflict. It looks like this:

$ git merge testing
Auto-merging index.html
CONFLICT (content): Merge conflict in index.html
Automatic merge failed; fix conflicts and then commit the result.

To resolve:

Run git status to verify all the files that could not be merged

Open up the file(s) with a conflict

<<<<<<< HEAD:index.html
<div id="footer">contact : email.support@github.com</div>
=======
<div id="footer">
 please contact us at support@github.com
</div>
>>>>>>> iss53:index.html

Resolve the conflict and remove any markers added by Git

Run git add on any files you updates

Run git status to verify all conflicts have been resolved

$ git status
On branch master
All conflicts fixed but you are still merging.
  (use "git commit" to conclude merge)

Changes to be committed:

    modified:   index.html

Run git commit -m "Message"

Class Exercise: Most Important & Most Confusing

2 min

Describe the most important thing you learned about Git today
What is most confusing?

Remote Branches

origin is not special, it's the default name given when you clone a git repo

To view remote branches, use:

git remote -v

Pushing to remote branches

git push origin testing

Deleting a remote branch

git push origin --delete serverfix

Class Exercise