Understanding git submodule and "freezing" it at a specific commit hash or version

Question

Assuming the following project layout:-

mainrepo_git
    |____ .git
    |____ .gitmodules
    |____ proj            <------- directory containing the code files for mainrepo
            |____ 3rdpartysourcecode <-- directory containing upstream open source code
            |      |____ .git
            |      |____ 3rdpartyfiles
            |
            |____ mainrepofilesanddirectories  

mainrepo_git contains source code I am directly responsible for. I have read/write access and can push and pull directly to a remote git repository which I manage.

Nested inside mainrepo_git is a directory which I named 3rdpartysourcecode. This 3rdpartysourcecode directory is in fact another git repo (also commonly referred to as a "git submodule") which is pointing to an open source 3rd party git repository managed by other developers. I only have read access to it. No write access.

Is there any way of 'freezing' a specific commit hash of the git submodule in relation to a commit made in my main repository?

For example, if I am at (or I revert to) commit a12ucak in my mainrepo, my git submodule also gets reverted to a specific version which I tie to commit a12ucak? And when I switch to commit b349jdsak, my git submodule also gets reverted to a version which I tie to b349jdsak?

So my question is: there is a way to create a linkage between a specific commit in the main repo with a corresponding commit in the git submodule? In such a way where when I checkout that specific commit in the main git repo, the corresponding commit in the git submodule will also be checkout.

Answer 1

Freezing is the whole point of submodules. You should really read a tutorial on it. In a nutshell, git add 3rdpartysourcecode (important no trailing slash!) followed by a commit locks the currently checked out submodule commit to the supermodule commit. Then later you use git submodule update to check out that revision.