Writing a tree object to the database
by Jakub Narębski, Rasmus Voss, Aske Olsson, Ferdinando Santacroce
Git: Mastering Version Control
- Git: Mastering Version Control
- Table of Contents
- Git: Mastering Version Control
- Git: Mastering Version Control
- Credits
- Preface
- I. Module 1
- 1. Getting Started with Git
- 2. Git Fundamentals – Working Locally
- 3. Git Fundamentals – Working Remotely
- 4. Git Fundamentals – Niche Concepts, Configurations, and Commands
- Dissecting the Git configuration
- Configuration architecture
- Configuration levels
- Listing configurations
- Editing configuration files manually
- Setting up other environment configurations
- Basic configurations
- 5. Obtaining the Most – Good Commits and Workflows
- The art of committing
- Adopting a workflow – a wise act
- Summary
- 6. Migrating to Git
- 7. Git Resources
- II. Module 2
- 1. Navigating Git
- 2. Configuration
- 3. Branching, Merging, and Options
- 4. Rebase Regularly and Interactively, and Other Use Cases
- 5. Storing Additional Information in Your Repository
- 6. Extracting Data from the Repository
- 7. Enhancing Your Daily Work with Git Hooks, Aliases, and Scripts
- Introduction
- Using a branch description in the commit message
- Creating a dynamic commit message template
- Using external information in the commit message
- Preventing the push of specific commits
- Configuring and using Git aliases
- Configuring and using Git scripts
- Setting up and using a commit template
- 8. Recovering from Mistakes
- Introduction
- Undo – remove a commit completely
- Undo – remove a commit and retain the changes to files
- Undo – remove a commit and retain the changes in the staging area
- Undo – working with a dirty area
- Redo – recreate the latest commit with new changes
- Revert – undo the changes introduced by a commit
- Reverting a merge
- Viewing past Git actions with git reflog
- Finding lost changes with git fsck
- 9. Repository Maintenance
- Introduction
- Pruning remote branches
- Running garbage collection manually
- Turning off automatic garbage collection
- Splitting a repository
- Rewriting history – changing a single file
- Back up your repositories as mirror repositories
- A quick submodule how-to
- Subtree merging
- Submodule versus subtree merging
- 10. Patching and Offline Sharing
- 11. Git Plumbing and Attributes
- Introduction
- Displaying the repository information
- Displaying the tree information
- Displaying the file information
- Writing a blob object to the database
- Writing a tree object to the database
- Writing a commit object to the database
- Keyword expansion with attribute filters
- Metadata diff of binary files
- Storing binaries elsewhere
- Checking the attributes of a file
- Attributes to export an archive
- 12. Tips and Tricks
- III. Module 3
- 1. Git Basics in Practice
- An introduction to version control and Git
- Git by example
- Repository setup
- Creating a Git repository
- Cloning the repository and creating the first commit
- Publishing changes
- Examining history and viewing changes
- Renaming and moving files
- Updating your repository (with merge)
- Creating a tag
- Resolving a merge conflict
- Adding files in bulk and removing files
- Undoing changes to a file
- Creating a new branch
- Merging a branch (no conflicts)
- Undoing an unpublished merge
- Summary
- 2. Exploring Project History
- 3. Developing with Git
- 4. Managing Your Worktree
- Ignoring files
- File attributes
- Fixing mistakes with the reset command
- Stashing away your changes
- Managing worktrees and the staging area
- Multiple working directories
- Summary
- 5. Collaborative Development with Git
- 6. Advanced Branching Techniques
- Types and purposes of branches
- Branching workflows and release engineering
- Interacting with branches in remote repositories
- Summary
- 7. Merging Changes Together
- 8. Keeping History Clean
- An introduction to Git internals
- Rewriting history
- Amending history without rewriting
- Summary
- 9. Managing Subprojects – Building a Living Framework
- Managing library and framework dependencies
- Managing large Git repositories
- Summary
- 10. Customizing and Extending Git
- 11. Git Administration
- 12. Git Best Practices
- 1. Git Basics in Practice
- A. Bibliography
- Index
- Configuration architecture
- Dissecting the Git configuration
Now, we have manually created objects in the Git database, but as nothing point to these objects, we have to remember them by their SHA-1 identifier. Furthermore, only the content of the files is stored in the database, so we learn to create a tree object that will refer to the blobs created.
We'll use the same repository of the last examples with the objects we created in the database.
We'll start by adding the first version of mytest.txt as follows:
$ git update-index --add --cacheinfo 100644 926e8ffd3258ed6edd1e254438f02fd24e417acc mytest.txt
Now we can write the content of the staging area to the database:
$ git write-tree 4c4493f8029d491d280695e263e24772ab6962ce
We can update and write a tree for the second version of mytest.txt as follows:
$ git update-index --cacheinfo 100644 6b3da706d14c3820597ec7109f163bc144dcbb22 mytest.txt $ git write-tree 2b9697438318f3a62a5e85d14a3b52d69b962907
Finally, we can use the object we created from stdin and we'll put it in a subdirectory, sub, with the name other.txt:
$ git update-index --add --cacheinfo 100644 70bacd9f51c26d602f474bbdc9f60644aa449e97 sub/other.txt $ git write-tree 9387b1a7619c6d899d83fe8d1437864bcd88736c
The update-index command updates the staging area with the files or content specified. The --add command tells Git to add a new file to the index, and the --cacheinfo switch is used to tell the command to use an existing object from the database. The 100644 command is used to create a normal file. Other types are 100755 (the executable file) and 040000 (a subdirectory), and so on. We could also have used a file directly for the update-index command, and then just provided the filename and omitted --cacheinfo, filetype, and identifier.
We can check the objects created with the cat-file command and verify their types, as shown in the following snippet:
$ git cat-file -p 4c4493f8029d491d280695e263e24772ab6962ce 100644 blob 926e8ffd3258ed6edd1e254438f02fd24e417acc mytest.txt $ git cat-file -t 4c4493f8029d491d280695e263e24772ab6962ce tree $ git cat-file -p 2b9697438318f3a62a5e85d14a3b52d69b962907 100644 blob 6b3da706d14c3820597ec7109f163bc144dcbb22 mytest.txt $ git cat-file -t 2b9697438318f3a62a5e85d14a3b52d69b962907 tree $ git cat-file -p 9387b1a7619c6d899d83fe8d1437864bcd88736c 100644 blob 6b3da706d14c3820597ec7109f163bc144dcbb22 mytest.txt 040000 tree 4cbaf806ece93e483f2515a7cc7326e194844797 sub $ git cat-file -t 9387b1a7619c6d899d83fe8d1437864bcd88736c tree
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