What is the advantage of using git submodules over having a repo inside another repo with a gitignore?

Question

We've been looking into git submodules and we are wondering what advantage (if any) is there in having a repository using submodules verses having a repository within another repository with a .gitignore file.

Example without submodules:

mkdir a cd a git init touch test1.txt echo "b" > .gitignore git add . git commit -m "Adding test1.txt and gitignore" mkdir b cd b git init touch test2.txt git add . git commit -m "Adding test2.txt" git log cd .. git log

AlBlue · Accepted Answer · 2009-09-22 21:36:33Z

20

The git parent (of the submodules) will keep track of the branches and tag IDs of the submodules when you commit. That will ensure that when you check out the parent (at a known version) then the submodules will also contain their right tags.

If, as above, it just happens to be an ignored subdirectory, then basically these are two independent git repos, as if they'd not been part of a file system hierarchy.

answered Sep 22, 2009 at 21:36

AlBlue

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4 Comments

Dan Moulding Over a year ago

This is exactly the key differentiator: using submodules you have a versioned object in the parent repository that represents the submodule. Nested (and ignored) sub-repositories have no representation at all in the parent repo.

Aditya M P Over a year ago

Hi, I'm having a problem understanding this: let's say the working repo is A and the submodule repo is b. Do you mean that b keeps track of changes made to its code within A? Could you please provide an example?

JRomero Over a year ago

@adityamenon I've viewed it as an organized way of being able to do git submodule foreach git pull without remembering where my "submodules" are.

Smily Over a year ago

@AdityaMP let's say you have repo A as a web app. A has a backend B and a frontend F, and they work together. Now, let's assume B has 3 versions, and F has 2: B1 works with F1, B2 and B3 works with F2, and B4 works with F3. If it were just folders, a single commit does not guarantee compatible versions, but if we are using submodules, then each commit can link compatible versions.

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