Understanding Git: Architecture and object model

Git can be somewhat difficult to grasp for the beginner. Let's unwrap how it works

Transcript

1. Understanding Git Pierre GOUDJO Architecture and object model
3. Jesse Du ff i eld — Creator of LazyGit You've heard it before, git is powerful, but what good is that power when everything is so damn hard to do? … YOU HAVE GOT TO BE KIDDING ME!
6. Understanding Git core model helps make sense of the commands
9. blob index.js Git stores snapshots of fi les in blob objects
10. blob index.js blob README Git stores snapshots of fi les in blob objects
11. blob index.js blob README blob core.js Git stores snapshots of fi les in blob objects
12. blob blob blob Git stores fi le hierarchies in trees tree . tree lib index.js README core.js
13. “Index 1.0” “README 1.0” “Core 1.0” Git is a content-addressable fi lesystem tree . tree lib index.js README core.js
14. “Index 1.0” “README 1.0” “Core 1.0” Git is a content-addressable fi lesystem tree . tree lib index.js README core.js 3c4e9c fa49b0 d8329f 1f7a7a 83baae
15. “Index 2.0” “README 1.0” “Core 1.0” Git is a content-addressable fi lesystem tree . tree lib index.js README core.js fa49b0 d8329f 7d235a 83baae
16. “Index 2.0” “README 1.0” “Core 1.0” Git is a content-addressable fi lesystem tree . tree lib index.js README core.js c45f23 fa49b0 d8329f 7d235a 83baae
17. “Index 2.0” “README 1.0” “Core 1.0” Git is a content-addressable fi lesystem tree . tree lib index.js README core.js “Display 1.0” display.js fa49b0 7d235a 83baae
18. “Index 2.0” “README 1.0” “Core 1.0” Git is a content-addressable fi lesystem tree . tree lib index.js README core.js “Display 1.0” display.js 4578fd fa49b0 a234f2 7d235a 83baae 4a8d75
19. “Index 2.0” “README 1.0” “Core 2.0” tree . tree lib index.js README core.js “Display 1.0” display.js fa49b0 7d235a 4a8d75
20. “Index 2.0” “README 1.0” “Core 2.0” tree . tree lib index.js README core.js “Display 1.0” display.js 78d321 fa49b0 ab5423 7d235a 55f321 4a8d75
21. “Index 2.0” “README 1.0” “Core 2.0” With tree and objects, Git can represent snapshots of tracked directories at any given time tree . tree lib index.js README core.js “Display 1.0” display.js 78d321 fa49b0 ab5423 7d235a 55f321 4a8d75
22. But that’s not enough to be used as an SCM
23. tree 78d321 tree a234f2 lib “Index 2.0” 7d235a “README 1.0” fa49b0 “Content 2.1” 54fd32 index.js README
24. The commit add context to a snapshot tree 78d321 tree a234f2 lib “Index 2.0” 7d235a “README 1.0” fa49b0 commit 1 45fad1 Pierre 12/10/2021 “Content 2.1” 54fd32 index.js README
25. commit 1 The history can be reconstructed by following the ancestor tree
26. commit 2 commit 1 The history can be reconstructed by following the ancestor tree
27. commit 4 commit 3 commit 2 commit 1 The history can be reconstructed by following the ancestor tree
28. Commits encode link to a snapshot and some metadata like the author, the reason of the change, the date…
31. Branches don’t really exist
32. Branches don’t really exist Remotes and tags neither
34. reference Let’s talk about references
35. Without references, you would still have to remember the commit SHA-1 commit 1 a234f2
36. refs/heads/master Without references, you would still have to remember the commit SHA-1 commit 1 a234f2
37. refs/heads/master Without references, you would still have to remember the commit SHA-1 commit 1 a234f2
38. refs/heads/master Without references, you would still have to remember the commit SHA-1 commit 1 a234f2 commit 2 7d235a
39. Without references, you would still have to remember the commit SHA-1 commit 1 a234f2 commit 2 7d235a
40. Without references, you would still have to remember the commit SHA-1 commit 1 a234f2 commit 2 7d235a refs/heads/master
41. With references, we can also mimic tags commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/tags/v1.0
42. With references, we can also represent git objects retrieved from another repository commit 1 a234f2 commit 2 7d235a commit 3 8c535a refs/remotes/origin/ main refs/heads/main
43. When git fetch origin, you retrieve new objects from another repository and update the reference of the remote reference commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/remotes/origin/ main refs/heads/main refs/remotes/origin/ feature1
44. When git fetch origin, you retrieve new objects from another repository and update the reference of the remote reference commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/remotes/origin/ main refs/heads/main
45. How do you know where you are in the graph
46. HEAD indicate where you are commit 1 a234f2 commit 2 7d235a refs/heads/master HEAD
47. HEAD can be on a commit directly commit 1 a234f2 commit 2 7d235a refs/heads/master HEAD commit 3 7d235a
48. When a commit is created HEAD move to the new commit commit 1 a234f2 commit 2 7d235a refs/heads/master HEAD commit 3 7d235a commit 4 7d235a
49. commit 1 a234f2 commit 2 7d235a refs/heads/master HEAD commit 3 65df34
50. The ref is also modi fi ed when they are refs/head/refs/* commit 1 a234f2 commit 2 7d235a refs/heads/master HEAD commit 3 65df34
51. Git checkout is used to move HEAD
52. commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/remotes/origin/ main refs/heads/main refs/remotes/origin/ feature1 HEAD git checkout main
53. commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/remotes/origin/ main refs/heads/main refs/remotes/origin/ feature1 git checkout origin/main
54. commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/remotes/origin/ main refs/heads/main refs/remotes/origin/ feature1 git checkout origin/main
55. commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/remotes/origin/ main refs/heads/main refs/remotes/origin/ feature1 HEAD git checkout origin/main
56. commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/remotes/origin/ main refs/heads/main refs/remotes/origin/ feature1 git checkout origin/main commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/heads/main commit 5 4512fa
57. commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/remotes/origin/ main refs/heads/main refs/remotes/origin/ feature1 git checkout origin/main commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/heads/main commit 5 4512fa
58. commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/remotes/origin/ main refs/heads/main refs/remotes/origin/ feature1 git checkout origin/main commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/heads/main commit 5 4512fa HEAD
59. commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/remotes/origin/ main refs/heads/main refs/remotes/origin/ feature1 git fetch origin commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/heads/main commit 5 4512fa commit 5 4512fa
60. commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/remotes/origin/ main refs/heads/main refs/remotes/origin/ feature1 git fetch origin commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/heads/main commit 5 4512fa commit 5 4512fa
61. commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/remotes/origin/ main refs/heads/main refs/remotes/origin/ feature1 git fetch origin commit 1 a234f2 commit 2 7d235a commit 3 8c535a commit 4 4512fa refs/heads/main commit 5 4512fa commit 5 4512fa HEAD