Git Fundamentals: Branches, Commits, Merge, Rebase, and Conflict Resolution

Working Directory ──► Staging Area (Index) ──► Repository (.git/)
     (files)           (git add)               (git commit)

git log --oneline
# a3f4c2d feat: add orders pipeline
# b9e12f1 fix: correct null handling in customers
# c4d7a90 init: project setup

# One-time global setup
git config --global user.name  "Asma Hafeez"
git config --global user.email "asma@example.com"
git config --global core.editor "code --wait"   # VS Code
git config --global init.defaultBranch main
git config --global pull.rebase true             # prefer rebase over merge on pull

# Check config
git config --list

# Initialize a repo
git init my-project
cd my-project

# Or clone an existing repo
git clone https://github.com/company/data-pipeline.git
cd data-pipeline

# Check state
git status
git diff                    # unstaged changes
git diff --staged           # staged changes

# Stage and commit
git add src/pipeline.py
git add .                   # add all changes (use carefully)
git add -p                  # interactive patch — stage specific hunks

git commit -m "feat: add orders ingestion pipeline"

# Push to remote
git push origin main
git push -u origin feature/orders   # -u sets upstream for this branch

# List branches
git branch          # local
git branch -a       # all including remote

# Create and switch
git checkout -b feature/customer-dim   # old style
git switch -c feature/customer-dim     # modern (Git 2.23+)

# Switch to existing
git checkout main
git switch main

# Delete
git branch -d feature/done            # safe delete (fails if unmerged)
git branch -D feature/abandoned       # force delete

# Rename
git branch -m old-name new-name

# Push a new branch
git push -u origin feature/customer-dim

git switch main
git merge feature/orders-pipeline

main:    A ── B ── C ──────── M
                   \         /
feature:            D ── E ──

git switch feature/orders-pipeline
git rebase main

Before:  main: A ── B ── C
         feature:  D ── E

After:   main: A ── B ── C
         feature:          D' ── E'   (new commits, same changes)

# Standard workflow
git switch feature/my-feature
git fetch origin
git rebase origin/main    # bring your branch up-to-date
# resolve any conflicts
git push --force-with-lease origin feature/my-feature  # must force-push after rebase

git rebase -i HEAD~4   # last 4 commits

pick a3f4c2d add orders pipeline draft
pick b9e12f1 fix typo
pick c4d7a90 fix another typo
pick d1e2f3g add logging to pipeline

# Commands:
# p, pick   = use commit
# r, reword = use commit, but edit the message
# e, edit   = use commit, but stop for amending
# s, squash = meld into previous commit
# f, fixup  = like squash, but discard this commit's message
# d, drop   = remove commit

pick a3f4c2d add orders pipeline draft
s    b9e12f1 fix typo
s    c4d7a90 fix another typo
r    d1e2f3g add logging to pipeline

git merge feature/orders-pipeline
# CONFLICT (content): Merge conflict in src/pipeline.py

def process_orders():
<<<<<<< HEAD
    return fetch_from_api()
=======
    return fetch_from_database()
>>>>>>> feature/orders-pipeline

def process_orders():
    # Resolved: use API as primary, database as fallback
    return fetch_from_api() or fetch_from_database()

git add src/pipeline.py
git commit    # or git rebase --continue

git config --global merge.tool vscode
git mergetool   # opens VS Code's 3-way merge view

git stash                           # stash all changes
git stash push -m "WIP: orders fix" # stash with a name

git stash list                      # view all stashes
# stash@{0}: WIP: orders fix
# stash@{1}: On main: temp experiments

git stash pop                       # apply latest stash + remove it
git stash apply stash@{1}          # apply specific stash (keep it in list)
git stash drop stash@{0}           # delete a stash
git stash clear                    # delete all stashes

# Stash including untracked files
git stash push -u -m "with new files"

# View history
git log --oneline --graph --all     # visual branch graph
git log --author="Asma" --since="1 week ago"
git show a3f4c2d                    # view a specific commit

# Undo changes
git restore src/pipeline.py         # discard unstaged changes to a file
git restore --staged src/pipeline.py  # unstage (keep changes)
git reset --soft HEAD~1             # undo last commit, keep changes staged
git reset --mixed HEAD~1            # undo last commit, unstage changes (default)
git reset --hard HEAD~1             # undo last commit, DISCARD changes (destructive!)

# Find commits
git log -S "def process_orders"     # find when this string was added/removed
git log --all --full-history -- "src/deleted_file.py"  # find deleted file

# Cherry-pick: apply a specific commit to current branch
git cherry-pick a3f4c2d

# Reflog — your safety net
git reflog                          # shows all HEAD movements
git reset --hard HEAD@{3}          # go back 3 steps in reflog

# Python
__pycache__/
*.pyc
*.pyo
.venv/
*.egg-info/
dist/
.pytest_cache/

# Environment
.env
.env.local
.env.production
*.local

# dbt
target/
dbt_packages/
logs/
.user.yml

# IDE
.vscode/
.idea/
*.swp
.DS_Store

# Secrets
*.pem
*.key
*.p12
credentials.json
service_account.json

(): 

[optional body]

[optional footer]

feat:      new feature
fix:       bug fix
docs:      documentation only
style:     formatting (no logic change)
refactor:  code change, no feature/fix
test:      adding tests
chore:     tooling, config, deps
perf:      performance improvement
ci:        CI/CD changes

feat(orders): add incremental ingestion from API
fix(customers): handle null email in SCD Type 2 merge
docs: update README with local setup instructions
refactor(pipeline): extract validation into separate module
test(orders): add integration tests for CDC loading
ci: add slim dbt CI with state:modified