Git Staging区域的功能

Question

I have gone through Git object model and read other articles about git but couldn't understand clearly about Git staging area .

What does staging area actually do?

Does it create the blob object and tree object when we do git add and when we do git commit the commit object is linked to the parent commit and corresponding tree object which is already linked to it's blob/tree object?

Or

Does it just stores the info in index file (that something is changed and when we do git add it says ready for commit) and when we do git commit all the objects creation and linking happen between commit, tree, blob objects?

Answer 1

"Staging area" is convenience jargon for the most common and popular way to use the index. Your first option,

Does it create the blob object and tree object when we do git add and when we do git commit the commit object is linked to the parent commit and corresponding tree object which is already linked to it's blob/tree object?

has it almost exactly right: git add puts what you added in the repo, and git commit ties the commit object to the parent commit and the corresponding tree object - - - but that corresponding tree object isn't in the repo yet, git commit builds the tree (that ties pathnames to content) by consulting the index, which is exactly what it says it is: an index, tying pathnames to content.

So, git checkout updates the index to point to the content it checked out at each checked-out path, and git add updates the index to point to the content it added for each added path.

So you can use this as a "staging area", git commit only cares what you've added, not what's in your worktree. This is why git checkout , git reset , git commit and git add all have --patch options: there's what you checked out, what you've added, and what's in your worktree. At any point it might be useful to see differences between any of those, or "take back" part of the changes you made, maybe because they belong in another commit or just need further work.

Answer 2

The staging area is a file, generally contained in your Git directory, that stores information about what will go into your next commit. Its technical name in Git parlance is the index , but the phrase staging area works just as well.

To stage a file is simply to prepare it finely for a commit. Git, with its index allows you to commit only certain parts of the changes you've done since the last commit. Say you're working on two features - one is finished, and one still needs some work done. You'd like to make a commit and go home but wouldn't like to commit the parts of the second feature, which is not done yet. You stage the parts you know belong to the first feature, and commit. Now your commit is your project with the first feature done, while the second is still in work-in-progress in your working directory.

git add adds your modified files to the queue to be committed later. Files are not committed

git commit commits the files that have been added and creates a new revision with a log... If you do not add any files, git will not commit anything. You can combine both actions with git commit -a

git push pushes your changes to the remote repository.

You do a commit, which takes the files as they are in the staging area and stores that snapshot permanently to your Git directory. Read more info : https://git-scm.com/book/en/v2/Getting-Started-Git-Basics