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In the previous video, I mentioned that you're generally going to want to check out the `master` branch before creating any topic branches. It's a good idea to ensure your topic branch is based on the `master` branch, if you're planning to merge it back into `master`. Let's take a look at what happens if we create a new branch when a different branch is checked out.
- I'm going to redo my creation of the
add-lettersbranch.- But this time I'm going to do it with the
testingbranch checked out instead ofmaster:git checkout testing - The
testingbranch includes the two commits that set up our unit tests:git log - Now let me create and check out a new version of the
add-lettersbranch, with a slightly different name:git checkout -b add-letters-2
- But this time I'm going to do it with the
- I'll make the same update to the
decoder.rbfile that I did in the previous video:
1 => 'A',
2 => 'B',
3 => 'C',
4 => 'D',
5 => 'E',
- Now I'll stage that file:
git add decoder.rb - And I'll commit it:
git commit -m "Add A-E" - If I run
git lognow, we'll see the commits for thisadd-letters-2branch:git log - We'll see the new commit we just added, which is identical to the commit we made to the
add-lettersbranch in the previous video. - And below that, we'll see that the log includes the commits that add unit tests!
commit 389e26b7170e0697061c32ea42388d4046090ad2 (HEAD -> add-letters-2)
Author: Jay McGavren <me@example.com>
Date: Fri Sep 28 12:08:50 2018 -0700
Add A-E
commit 01c21ced52c664acf1362fa003ffc47bcde838ce (testing)
Author: Jay McGavren <me@example.com>
Date: Wed Sep 26 20:00:18 2018 -0700
Add test with more letters
commit 7bec24095bd1604e647912e6a8d4a0ff8061c129
Author: Jay McGavren <me@example.com>
Date: Wed Sep 26 16:24:57 2018 -0700
Add unit test
commit 21428a2eee8e55becb6da879228446746ad6f1a8 (master)
Author: Jay McGavren <me@example.com>
Date: Tue Sep 25 08:34:12 2018 -0700
Add main program
...
- Because the
testingbranch was checked out when we created theadd-letters-2branch, all the commits in thetestingbranch are now included in theadd-letters-2branch. - We don't want that. Our unit tests may not be done yet, and we may want to make changes to them. For now, at least, we want commits related to unit tests to exist on the
testingtopic branch, and only thetestingbranch. - Here's something else interesting: those commits still exist on the
testingbranch as well.- We can confirm this by checking out
testing:git checkout testing - If we display the log:
git log - ...We'll see the commits to set up unit tests there as well.
- We can confirm this by checking out
commit 01c21ced52c664acf1362fa003ffc47bcde838ce (testing)
Author: Jay McGavren <me@example.com>
Date: Wed Sep 26 20:00:18 2018 -0700
Add test with more letters
commit 7bec24095bd1604e647912e6a8d4a0ff8061c129
Author: Jay McGavren <me@example.com>
Date: Wed Sep 26 16:24:57 2018 -0700
Add unit test
commit 21428a2eee8e55becb6da879228446746ad6f1a8 (master)
Author: Jay McGavren <me@example.com>
Date: Tue Sep 25 08:34:12 2018 -0700
Add main program
...
The two commits from the testing branch that we see on the add-letters-2 branch aren't duplicates of these commits, they are the exact same commits.
- Remember, we said that a branch is just a pointer to a particular commit.
- The history for a branch is determined by the commits themselves. Every commit has a "parent", that is, another commit that it's based on.
- Any Git command that needs to access your branch history looks at each commit, then moves to its parent.
- This is true even for commits on a new branch. The commit's parent may be a commit that another branch points to.
When we created the first add-letters branch, the master branch was checked out. So the commit that the master branch pointed to was used as the parent of the first commit on the add-letters branch.
But when we created the add-letters-2 branch, the testing branch was checked out. The commit that the testing branch pointed to was used as the parent of the first add-letters-2 commit. This is why the two commits that set up unit tests appear on both the testing and add-letters-2 branches.
If we tried to merge the add-letters-2 branch into the master branch later, it would be an even bigger problem.
- The commits from the
testingbranch would be merged into themasterbranch, because they're also part of theadd-letters-2branch. They'd be included even if they weren't ready.
Cherry-picking commits
There's a way to select only particular commits from a branch: the git cherry-pick command. You can read more about it here.
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In the previous video I mentioned that
you're generally going to want to check
0:00
out the master branch before
creating any topic branches.
0:04
It's a good idea to ensure your topic
branch is based on the master branch
0:07
if you're planning to
merge it back into master.
0:11
Let's take a look at what happens
if we create a new branch when
0:14
a different branch is checked out.
0:17
I'm going to redo my creation
of the add-letters branch.
0:20
But this time, I'm gonna do it with
the testing branch checked out,
0:23
instead of master.
0:25
The testing branch includes the two
commits that set up our unit test.
0:27
Now, let me create and check out a new
version of the add-letters branch with
0:33
a slightly different name,
git checkout-b add-letters-2.
0:36
I'll make the same update to
the decoder.rb file that I did
0:41
in the previous video.
0:44
Now, I'll stage that file,
git add decoder.rb.
0:50
And I'll commit it,
git commit -m add a through e.
0:55
If I run git log now, we'll see
the commits for this add-letters-2 branch.
1:01
We'll see the new commit we just added,
which is identical to the commit we made
1:06
to the add-letters branch
in the previous video.
1:09
And below that, we'll see that the log
includes the commits that add unit tests.
1:12
Because the testing branch was checked out
when we created the add letters-2 branch,
1:21
all the commits in the testing branch are
now included in the add-letters-2 branch.
1:25
We don't want that.
1:30
Our unit tests may not be done yet, and
we may want to make changes to them.
1:31
For now at least, we want commits related
to unit tests to exist on the testing
1:35
topic branch, and only the testing branch.
1:39
Here's something else interesting.
1:43
Those commits still exist on
the testing branch as well.
1:45
We can confirm this by checking
out testing, git checkout testing.
1:48
And if we display the log,
1:55
we'll see the commits to set
up unit tests there as well.
1:56
The two commits from the testing branch
that we see on the add-letters-2
2:04
branch aren't duplicates of these commits,
they are the exact same commits.
2:08
Remember, we said that a branch is
just a pointer to a particular commit.
2:13
The history for a branch is
determined by the commits themselves.
2:17
Every commit has a parent, that is,
another commit that it's based on.
2:21
When you run git log, git starts with
the commit that your branch points to, and
2:26
prints its info.
2:30
Then it checks what that commit's parent
is, and prints the parent's info.
2:31
And so on, up the chain, until you have
a complete history for that branch.
2:35
The same process is used for
2:40
any other command that needs
to access your branch history.
2:42
This is true, even for
commits on a new branch.
2:45
Git log looks at the commit
the branch points to and
2:48
prints its info,
then it looks at that commit's parent.
2:51
The parent may be a commit
that another branch points to.
2:54
But that doesn't matter to git,
it just keeps looking at each commit,
2:57
printing its info and
then jumping to that commit's parent.
3:01
When created the first add-letters branch,
the Master branch was checked out.
3:05
So the commit that the Master branch
pointed to was used as the parent of
3:10
the first commit on
the add-letters branch.
3:13
But when we created
the add-letters-2 branch,
3:16
the testing branch was checked out.
3:18
The commit that that testing branch
pointed to was used as the parent of
3:20
the first add-letters-2 commit.
3:24
This is why the two commits that set up
unit tests appear on both the testing and
3:26
add-letters-2 branches.
3:31
When the testing branch is checked out and
3:33
you run git log, git prints the commit
that the testing branch refers to.
3:35
Then, it looks at that commit's parent,
and so
3:39
on up the chain to build a complete
history for the testing branch.
3:41
The process is the same when
the add-letters-2 branch is checked out.
3:45
git log prints the commit that
the add-letters-2 branch points to,
3:49
then it looks at that commit's parent,
3:53
which is also the commit pointed
to by the testing branch.
3:54
If we tried to merge the add-letters-2
branch into the master branch later,
3:58
it would be even a bigger problem.
4:02
The commits from the testing branch
will be merged into the master branch
4:04
because they are also part
of the add-letters-2 branch.
4:08
They'd be included even
if they weren't ready.
4:11
There are ways to select only
particular commits from a branch,
4:13
which you can read about in
the teacher's notes if you want.
4:16
But they're advanced and
somewhat error prone.
4:19
It's better to ensure your branch is
based on the branch you're going to
4:22
merge it into, so
that you can just merge the whole branch.
4:25
Aside from the parent commit,
the add-letters and
4:29
add-letters-2 branches are identical.
4:31
So I'm going to go ahead and
delete the add-letters-2 branch.
4:34
Don't worry about memorizing
these delete commands right now.
4:37
We'll be covering how to delete branches
in detail in an upcoming stage.
4:40
I can't delete a branch
that's checked out.
4:44
So first, I'm going to switch to
a different branch, git checkout master.
4:47
Now, I'll use the uppercase D flag to get
branch to force deletion of the branch.
4:51
Git branch -D add-letters-2.
4:56
In the next video,
5:00
we'll show you how to display
the differences between two branches.
5:00
See you there.
5:04
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